A Survey of Research Progress and Development Tendency of Attribute-Based Encryption
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paper_title: Improving privacy and security in multi-authority attribute-based encryption

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Attribute based encryption (ABE) [13] determines decryption ability based on a user's attributes. In a multi-authority ABE scheme, multiple attribute-authorities monitor different sets of attributes and issue corresponding decryption keys to users, and encryptors can require that a user obtain keys for appropriate attributes from each authority before decrypting a message. Chase [5] gave a multi-authority ABE scheme using the concepts of a trusted central authority (CA) and global identifiers (GID). However, the CA in that construction has the power to decrypt every ciphertext, which seems somehow contradictory to the original goal of distributing control over many potentially untrusted authorities. Moreover, in that construction, the use of a consistent GID allowed the authorities to combine their information to build a full profile with all of a user's attributes, which unnecessarily compromises the privacy of the user. In this paper, we propose a solution which removes the trusted central authority, and protects the users' privacy by preventing the authorities from pooling their information on particular users, thus making ABE more usable in practice.
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paper_title: A ciphertext-policy attribute-based encryption scheme with constant ciphertext length

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An Attribute-Based Encryption (ABE) is an encryption scheme where users with some attributes can decrypt ciphertexts associated with these attributes. The length of the ciphertext depends on the number of attributes in previous ABE schemes. In this paper, we propose a new Ciphertext-Policy Attribute-Based Encryption (CP-ABE) with constant ciphertext length. In our scheme, the number of pairing computations is also constant. In addition, the number of additional bits required from chosen plaintext attack-secure CP-ABE to chosen ciphertext attack-secure CP-ABE is reduced by 90% with respect to that of the previous scheme.
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paper_title: Fully secure multi-authority ciphertext-policy attribute-based encryption without random oracles

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Recently Lewko and Waters proposed the first fully secure multi-authority ciphertext-policy attribute-based encryption (CP-ABE) system in the random oracle model, and leave the construction of a fully secure multi-authority CP-ABE in the standard model as an open problem. Also, there is no CP-ABE system which can completely prevent individual authorities from decrypting ciphertexts. In this paper, we propose a new multi-authority CP-ABE system which addresses these two problems positively. In this new system, there are multiple Central Authorities (CAs) and Attribute Authorities (AAs), the CAs issue identity-related keys to users and are not involved in any attribute related operations, AAs issue attribute-related keys to users and each AA manages a different domain of attributes. The AAs operate independently from each other and do not need to know the existence of other AAs. Messages can be encrypted under any monotone access structure over the entire attribute universe. The system is adaptively secure in the standard model with adaptive authority corruption, and can support large attribute universe.
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paper_title: A method for obtaining digital signatures and public-key cryptosystems

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An encryption method is presented with the novel property that publicly revealing an encryption key does not thereby reveal the corresponding decryption key. This has two important consequences: (1) Couriers or other secure means are not needed to transmit keys, since a message can be enciphered using an encryption key publicly revealed by the intented recipient. Only he can decipher the message, since only he knows the corresponding decryption key. (2) A message can be “signed” using a privately held decryption key. Anyone can verify this signature using the corresponding publicly revealed encryption key. Signatures cannot be forged, and a signer cannot later deny the validity of his signature. This has obvious applications in “electronic mail” and “electronic funds transfer” systems. A message is encrypted by representing it as a number M, raising M to a publicly specified power e, and then taking the remainder when the result is divided by the publicly specified product, n , of two large secret primer numbers p and q. Decryption is similar; only a different, secret, power d is used, where e * d ≡ 1(mod (p - 1) * (q - 1)). The security of the system rests in part on the difficulty of factoring the published divisor, n .
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paper_title: Provably secure ciphertext policy ABE

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In ciphertext policy attribute-based encryption (CP-ABE), every secret key is associated with a set of attributes, and every ciphertext is associated with an access structure on attributes. Decryption is enabled if and only if the user's attribute set satisfies the ciphertext access structure. This provides fine-grained access control on shared data in many practical settings, e.g., secure database and IP multicast. In this paper, we study CP-ABE schemes in which access structures are AND gates on positive and negative attributes. Our basic scheme is proven to be chosen plaintext (CPA) secure under the decisional bilinear Diffie-Hellman (DBDH) assumption. We then apply the Canetti-Halevi-Katz technique to obtain a chosen ciphertext (CCA) secure extension using one-time signatures. The security proof is a reduction to the DBDH assumption and the strong existential unforgeability of the signature primitive. In addition, we introduce hierarchical attributes to optimize our basic scheme - reducing both ciphertext size and encryption/decryption time while maintaining CPA security. We conclude with a discussion of practical applications of CP-ABE.
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paper_title: ON MULTI-AUTHORITY CIPHERTEXT-POLICY ATTRIBUTE-BASED ENCRYPTION

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In classical encryption schemes, data is encrypted under a single key that is associated with a user or group. In Ciphertext-Policy Attribute-Based Encryption(CP-ABE) keys are associated with attributes of users, given to them by a central trusted authority, and data is en- crypted under a logical formula over these attributes. We extend this idea to the case where an arbitrary number of independent parties can be present to maintain attributes and their corresponding secret keys. We present a scheme for multi-authority CP-ABE, propose the first two constructions that fully implement the scheme, and prove their security against chosen plaintext attacks.
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paper_title: Dual-Policy Attribute Based Encryption

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We present a new variant of Attribute based encryption (ABE) called Dual-Policy ABE. Basically, it is a conjunctively combined scheme between Key-Policy and Ciphertext-Policy ABE, the two previous available types of ABE. Dual-Policy ABE allows simultaneously two access control mechanisms over encrypted data: one involves policies over objective attributes ascribed to data and the other involves policies over subjective attributes ascribed to user credentials. The previous two types of ABE can only allow either functionality above one at a time.
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paper_title: Secure attribute-based systems

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Attributes define, classify, or annotate the datum to which they are assigned. However, traditional attribute architectures and cryptosystems are ill-equipped to provide security in the face of diverse access requirements and environments. In this paper, we introduce a novel secure information management architecture based on emerging attribute-based encryption (ABE) primitives. A policy system that meets the needs of complex policies is defined and illustrated. Based on the needs of those policies, we propose cryptographic optimizations that vastly improve enforcement efficiency. We further explore the use of such policies in two example applications: a HIPAA compliant distributed file system and a social network. A performance analysis of our ABE system and example applications demonstrates the ability to reduce cryptographic costs by as much as 98% over previously proposed constructions. Through this, we demonstrate that our attribute system is an efficient solution for securely managing information in large, loosely-coupled, distributed systems.
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paper_title: Attribute-based encryption with partially hidden encryptor-specified access structures

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We propose attribute-based encryption schemes where encryptor-specified access structures (also called ciphertext policies) are hidden. By using our schemes, an encryptor can encrypt data with a hidden access structure. A decryptor obtains her secret key associated with her attributes from a trusted authority in advance and if the attributes associated with the decryptor's secret key do not satisfy the access structure associated with the encrypted data, the decryptor cannot decrypt the data or guess even what access structure was specified by the encryptor. We prove security of our construction based on the Decisional Bilinear Diffie-Hellman assumption and the Decision Linear assumption. In our security notion, even the legitimate decryptor cannot obtain the information about the access structure associated with the encrypted data more than the fact that she can decrypt the data.
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paper_title: Multi-Authority Attribute Based Encryption

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In an identity based encryption scheme, each user is identified by a unique identity string. An attribute based encryption scheme (ABE), in contrast, is a scheme in which each user is identified by a set of attributes, and some function of those attributes is used to determine decryption ability for each ciphertext. Sahai and Waters introduced a single authority attribute encryption scheme and left open the question of whether a scheme could be constructed in which multiple authorities were allowed to distribute attributes [SW05]. We answer this question in the affirmative. ::: ::: Our scheme allows any polynomial number of independent authorities to monitor attributes and distribute secret keys. An encryptor can choose, for each authority, a number dk and a set of attributes; he can then encrypt a message such that a user can only decrypt if he has at least dk of the given attributes from each authority k. Our scheme can tolerate an arbitrary number of corrupt authoritites. ::: ::: We also show how to apply our techniques to achieve a multiauthority version of the large universe fine grained access control ABE presented by Gopal et al. [GPSW06].
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paper_title: Attribute-Based Encryption Supporting Direct/Indirect Revocation Modes

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Attribute-based encryption (ABE) enables an access control mechanism over encrypted data by specifying access policies among private keys and ciphertexts. In this paper, we focus on ABE that supports revocation. Currently, there are two available revocable ABE schemes in the literature. Their revocation mechanisms, however, differ in the sense that they can be considered as direct and indirect methods. Direct revocation enforces revocation directly by the sender who specifies the revocation list while encrypting. Indirect revocation enforces revocation by the key authority who releases a key update material periodically in such a way that only non-revoked users can update their keys (hence, revoked users' keys are implicitly rendered useless). An advantage of the indirect method over the direct one is that it does not require senders to know the revocation list. In contrast, an advantage of the direct method over the other is that it does not involve key update phase for all non-revoked users interacting with the key authority. In this paper, we present the first Hybrid Revocable ABE scheme that allows senders to select on-the-fly when encrypting whether to use either direct or indirect revocation mode; therefore, it combines best advantages from both methods.
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paper_title: Attribute-Based Access Control with Efficient Revocation in Data Outsourcing Systems

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Some of the most challenging issues in data outsourcing scenario are the enforcement of authorization policies and the support of policy updates. Ciphertext-policy attribute-based encryption is a promising cryptographic solution to these issues for enforcing access control policies defined by a data owner on outsourced data. However, the problem of applying the attribute-based encryption in an outsourced architecture introduces several challenges with regard to the attribute and user revocation. In this paper, we propose an access control mechanism using ciphertext-policy attribute-based encryption to enforce access control policies with efficient attribute and user revocation capability. The fine-grained access control can be achieved by dual encryption mechanism which takes advantage of the attribute-based encryption and selective group key distribution in each attribute group. We demonstrate how to apply the proposed mechanism to securely manage the outsourced data. The analysis results indicate that the proposed scheme is efficient and secure in the data outsourcing systems.
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paper_title: Privacy-Preserving Decentralized Key-Policy Attribute-Based Encryption

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Decentralized attribute-based encryption (ABE) is a variant of a multiauthority ABE scheme where each authority can issue secret keys to the user independently without any cooperation and a central authority. This is in contrast to the previous constructions, where multiple authorities must be online and setup the system interactively, which is impractical. Hence, it is clear that a decentralized ABE scheme eliminates the heavy communication cost and the need for collaborative computation in the setup stage. Furthermore, every authority can join or leave the system freely without the necessity of reinitializing the system. In contemporary multiauthority ABE schemes, a user's secret keys from different authorities must be tied to his global identifier (GID) to resist the collusion attack. However, this will compromise the user's privacy. Multiple authorities can collaborate to trace the user by his GID, collect his attributes, then impersonate him. Therefore, constructing a decentralized ABE scheme with privacy-preserving remains a challenging research problem. In this paper, we propose a privacy-preserving decentralized key-policy ABE scheme where each authority can issue secret keys to a user independently without knowing anything about his GID. Therefore, even if multiple authorities are corrupted, they cannot collect the user's attributes by tracing his GID. Notably, our scheme only requires standard complexity assumptions (e.g., decisional bilinear Diffie-Hellman) and does not require any cooperation between the multiple authorities, in contrast to the previous comparable scheme that requires nonstandard complexity assumptions (e.g., q-decisional Diffie-Hellman inversion) and interactions among multiple authorities. To the best of our knowledge, it is the first decentralized ABE scheme with privacy-preserving based on standard complexity assumptions.
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paper_title: A Survey on Attribute-based Encryption Schemes of Access Control in Cloud Environments

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In Attribute-based Encryption (ABE) scheme, attributes play a very important role. Attributes have been exploited to generate a public key for encrypting data and have been used as an access policy to control users' access. The access policy can be categorized as either key-policy or ciphertext-policy. The key-policy is the access structure on the user's private key, and the ciphertext-policy is the access structure on the ciphertext. And the access structure can also be categorized as either monotonic or non-monotonic one. Using ABE schemes can have the advantages: (1) to reduce the communication overhead of the Internet, and (2) to provide a fine-grained access control. In this paper, we survey a basic attribute-based encryption scheme, two various access policy attribute-based encryption schemes, and two various access structures, which are analyzed for cloud environments. Finally, we list the comparisons of these schemes by some criteria for cloud environments.
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paper_title: Multi-authority attribute-based encryption with honest-but-curious central authority

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An attribute-based encryption scheme capable of handling multiple authorities was recently proposed by Chase. The scheme is built upon a single-authority attribute-based encryption scheme presented earlier by Sahai and Waters. Chase's construction uses a trusted central authority that is inherently capable of decrypting arbitrary ciphertexts created within the system. We present a multi-authority attribute-based encryption scheme in which only the set of recipients defined by the encrypting party can decrypt a corresponding ciphertext. The central authority is viewed as ‘honest-but-curious’: on the one hand, it honestly follows the protocol, and on the other hand, it is curious to decrypt arbitrary ciphertexts thus violating the intent of the encrypting party. The proposed scheme, which like its predecessors relies on the Bilinear Diffie–Hellman assumption, has a complexity comparable to that of Chase's scheme. We prove that our scheme is secure in the selective ID model and can tolerate an honest-but-curious central authority.
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paper_title: Attribute-based encryption for fine-grained access control of encrypted data

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As more sensitive data is shared and stored by third-party sites on the Internet, there will be a need to encrypt data stored at these sites. One drawback of encrypting data, is that it can be selectively shared only at a coarse-grained level (i.e., giving another party your private key). We develop a new cryptosystem for fine-grained sharing of encrypted data that we call Key-Policy Attribute-Based Encryption (KP-ABE). In our cryptosystem, ciphertexts are labeled with sets of attributes and private keys are associated with access structures that control which ciphertexts a user is able to decrypt. We demonstrate the applicability of our construction to sharing of audit-log information and broadcast encryption. Our construction supports delegation of private keys which subsumesHierarchical Identity-Based Encryption (HIBE).
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paper_title: Ciphertext-policy attribute-based encryption: an expressive, efficient, and provably secure realization

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We present a new methodology for realizing Ciphertext-Policy Attribute Encryption (CP-ABE) under concrete and noninteractive cryptographic assumptions in the standard model. Our solutions allow any encryptor to specify access control in terms of any access formula over the attributes in the system. In our most efficient system, ciphertext size, encryption, and decryption time scales linearly with the complexity of the access formula. The only previous work to achieve these parameters was limited to a proof in the generic group model. ::: ::: We present three constructions within our framework. Our first system is proven selectively secure under a assumption that we call the decisional Parallel Bilinear Diffie-Hellman Exponent (PBDHE) assumption which can be viewed as a generalization of the BDHE assumption. Our next two constructions provide performance tradeoffs to achieve provable security respectively under the (weaker) decisional Bilinear-Diffie-Hellman Exponent and decisional Bilinear Diffie-Hellman assumptions.
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paper_title: Bounded Ciphertext policy attribute based encryption

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In a ciphertext policy attribute based encryption system, a user's private key is associated with a set of attributes (describing the user) and an encrypted ciphertext will specify an access policy over attributes. A user will be able to decrypt if and only if his attributes satisfy the ciphertext's policy. ::: ::: In this work, we present the first construction of a ciphertext-policy attribute based encryption scheme having a security proof based on a number theoretic assumption and supporting advanced access structures. Previous CP-ABE systems could either support only very limited access structures or had a proof of security only in the generic group model. Our construction can support access structures which can be represented by a bounded size access tree with threshold gates as its nodes. The bound on the size of the access trees is chosen at the time of the system setup. Our security proof is based on the standard Decisional Bilinear Diffie-Hellman assumption.
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paper_title: Using Threshold Attribute-based Encryption for Practical Biometric-based Access Control

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Threshold attribute-based encryption (thABE) is a variant of identity-based encryption which views identities as sets of descriptive attributes. If a thABE ciphertext c is computed for a set ω of attributes, then, to decrypt c, a user must have keys associated with a sufficiently large subset of ω. One application of thABE is biometric-based access control (BBAC). Practical BBAC applications impose the following constraints on the design of thABE schemes: first, a suitable thABE scheme must have an efficient decryption procedure; second, the proposed scheme must prevent colluding users from being able to decrypt ciphertexts which none of them could decrypt; third, the designed scheme must provide a mechanism whereby encryptors can, at encryption time, specify multiples sets of attributes with their corresponding threshold values. To the best of our knowledge, no scheme is known that simultaneously satisfies the aforementioned requirements. This paper describes an efficient and collusion-resistant thABE scheme featuring dynamically-specifiable threshold values. The proposed scheme is proven secure in the random oracle model, and its efficiency and flexibility are compared with Sahai and Waters'thABE scheme.
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paper_title: Provably secure and efficient bounded ciphertext policy attribute based encryption

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Ciphertext policy attribute based encryption (CPABE) allows a sender to distribute messages based on an access policy which can be expressed as a boolean function consisting of (OR, AND) gates between attributes. A receiver whose secret key is associated with those attributes could only decrypt a ciphertext successfully if and only if his attributes satisfy the ciphertext's access policy. Fine-grained access control, a new concept mentioned by GPSW in CCS'06 can realize a more delicate access policy which could be represented as an access tree with threshold gates connecting attributes. In ICALP'08, Goyal et al. design a bounded CPABE (denoted as GJPS) with fine-grained access policy which can be proven secure under a number-theoretic assumption. In this paper, we improve their scheme by providing faster encryption / decryption algorithm and shortened ciphertext size. Moreover, we use one-time signature technique to obtain a chosen ciphertext secure extension and give its complete security proof in the standard model under traditional Decisional Bilinear Diffie-Hellman (DBDH) assumption and strong existential unforgeability of one-time signature scheme.
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paper_title: Hierarchical attribute-based encryption and scalable user revocation for sharing data in cloud servers

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With rapid development of cloud computing, more and more enterprises will outsource their sensitive data for sharing in a cloud. To keep the shared data confidential against untrusted cloud service providers (CSPs), a natural way is to store only the encrypted data in a cloud. The key problems of this approach include establishing access control for the encrypted data, and revoking the access rights from users when they are no longer authorized to access the encrypted data. This paper aims to solve both problems. First, we propose a hierarchical attribute-based encryption scheme (HABE) by combining a hierarchical identity-based encryption (HIBE) system and a ciphertext-policy attribute-based encryption (CP-ABE) system, so as to provide not only fine-grained access control, but also full delegation and high performance. Then, we propose a scalable revocation scheme by applying proxy re-encryption (PRE) and lazy re-encryption (LRE) to the HABE scheme, so as to efficiently revoke access rights from users.
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paper_title: Improved multicast key management of Chinese wireless local area network security standard

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Multicasting is an important business in the field of the wireless local area network (WLAN), because the access point (AP) usually has to send the same message to each station (STA) of a specific group, and broadcasting the message to this group is one of the most efficient ways of communication. Chinese WLAN security standard, called WLAN Authentication and Privacy Infrastructure (WAPI), has taken secure multicasting into account, and proposed a Multicast Key Management Protocol (MKMP), in which the multicast session key (MSK) is distributed to each STA over the secure unicast channel built between STA and AP one by one. It is clear that the MSK distribution is very inefficient in performance, especially when the number of STAs is very large. In this study, a new MSK distribution protocol is proposed, and it can be used to substitute the original protocol in WAPI. Analyses show that the proposed protocol can achieve needed security requirements, and is more efficient than the original one in WAPI. Now, WAPI has been in the process of ISO/IEC standard building, and thus the authors think that their proposal can ameliorate WAPI largely and promote its ISO/IEC standard building.
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paper_title: Attribute based data sharing with attribute revocation

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Ciphertext-Policy Attribute Based Encryption (CP-ABE) is a promising cryptographic primitive for fine-grained access control of shared data. In CP-ABE, each user is associated with a set of attributes and data are encrypted with access structures on attributes. A user is able to decrypt a ciphertext if and only if his attributes satisfy the ciphertext access structure. Beside this basic property, practical applications usually have other requirements. In this paper we focus on an important issue of attribute revocation which is cumbersome for CP-ABE schemes. In particular, we resolve this challenging issue by considering more practical scenarios in which semi-trustable on-line proxy servers are available. As compared to existing schemes, our proposed solution enables the authority to revoke user attributes with minimal effort. We achieve this by uniquely integrating the technique of proxy re-encryption with CP-ABE, and enable the authority to delegate most of laborious tasks to proxy servers. Formal analysis shows that our proposed scheme is provably secure against chosen ciphertext attacks. In addition, we show that our technique can also be applicable to the Key-Policy Attribute Based Encryption (KP-ABE) counterpart.
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paper_title: Distributed Attribute-Based Encryption

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Ciphertext-Policy Attribute-Based Encryption (CP-ABE) allows to encrypt data under an access policy, specified as a logical combination of attributes. Such ciphertexts can be decrypted by anyone with a set of attributes that fits the policy. In this paper, we introduce the concept of Distributed Attribute-Based Encryption (DABE), where an arbitrary number of parties can be present to maintain attributes and their corresponding secret keys. This is in stark contrast to the classic CP-ABE schemes, where all secret keys are distributed by one central trusted party. We provide the first construction of a DABE scheme; the construction is very efficient, as it requires only a constant number of pairing operations during encryption and decryption.
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paper_title: Achieving Secure, Scalable, and Fine-grained Data Access Control in Cloud Computing

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Cloud computing is an emerging computing paradigm in which resources of the computing infrastructure are provided as services over the Internet. As promising as it is, this paradigm also brings forth many new challenges for data security and access control when users outsource sensitive data for sharing on cloud servers, which are not within the same trusted domain as data owners. To keep sensitive user data confidential against untrusted servers, existing solutions usually apply cryptographic methods by disclosing data decryption keys only to authorized users. However, in doing so, these solutions inevitably introduce a heavy computation overhead on the data owner for key distribution and data management when fine-grained data access control is desired, and thus do not scale well. The problem of simultaneously achieving fine-grainedness, scalability, and data confidentiality of access control actually still remains unresolved. This paper addresses this challenging open issue by, on one hand, defining and enforcing access policies based on data attributes, and, on the other hand, allowing the data owner to delegate most of the computation tasks involved in fine-grained data access control to untrusted cloud servers without disclosing the underlying data contents. We achieve this goal by exploiting and uniquely combining techniques of attribute-based encryption (ABE), proxy re-encryption, and lazy re-encryption. Our proposed scheme also has salient properties of user access privilege confidentiality and user secret key accountability. Extensive analysis shows that our proposed scheme is highly efficient and provably secure under existing security models.
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paper_title: Verifiable Attribute Based Encryption

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In this paper, we propose the notion of Verifiable Attribute-Based Encryption (VABE) and give two constructs of key-policy VABE. One is with a single authority, and the other is with multi authorities. Not only our schemes are proved secure as the previous ABE schemes, they also provide a verification property. This could not be trivially solved, such as trying random decryption. Adding the verification property has a few advantages: first, it allows the user to immediately check the correctness of the keys, if not, he only needs the authority to resend the corresponding shares, especially, in multiauthority case, if the key does not pass the check, the user only needs to ask the particular authority to resend its own part, without need to go to all the authorities; second, if the keys pass the verification but the user still does not rightly decrypt out the message, something might be wrong with the attributes or ciphertexts, then, the user has to contact with the encryptor; third, the trick used in this paper could also be used in the ciphertext-policy scenario. We formalize the notion of VABE and prove our schemes in our model.
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paper_title: Multi-authority ciphertext-policy attribute-based encryption with accountability

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Attribute-based encryption (ABE) is a promising tool for implementing fine-grained cryptographic access control. Very recently, motivated by reducing the trust assumption on the authority, and enhancing the privacy of users, a multiple-authority key-policy ABE system, together with a semi-generic anonymous key-issuing protocol, have been proposed by Chase and Chow in CCS 2009. Since ABE allows encryption for multiple users with attributes satisfying the same policy, it may not be always possible to associate a decryption key to a particular individual. A misbehaving user could abuse the anonymity by leaking the key to someone else, without worrying of being traced. In this paper, we propose a multi-authority ciphertext-policy (AND gates with wildcard) ABE scheme with accountability, which allows tracing the identity of a misbehaving user who leaked the decryption key to others, and thus reduces the trust assumptions not only on the authorities but also the users. The tracing process is efficient and its computational overhead is only proportional to the length of the identity.
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paper_title: Defending Against Key Abuse Attacks in KP-ABE Enabled Broadcast Systems

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Key-Policy Attribute-Based Encryption (KP-ABE) is a promising cryptographic primitive which enables fine-grained access control over sensitive data. However, key abuse attacks in KP-ABE may impede its wide application especially in copyright-sensitive systems. To defend against this kind of attacks, this paper proposes a novel KP-ABE scheme which is able to disclose any illegal key distributor’s ID when key abuse is detected. In our scheme, each bit of user ID is defined as an attribute and the user secret key is associated with his unique ID. The tracing algorithm fulfills its task by tricking the pirate device into decrypting the ciphertext associated with the corresponding bits of his ID. Our proposed scheme has the salient property of black box tracing, i.e., it traces back to the illegal key distributor’s ID only by observing the pirate device’s outputs on certain inputs. In addition, it does not require the pirate device’s secret keys to be well-formed as compared to some previous work. Our proposed scheme is provably secure under the Decisional Bilinear Diffie-Hellman (DBDH) assumption and the Decisional Linear (DL) assumption.
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paper_title: A Ciphertext-Policy Attribute-Based Proxy Re-encryption with Chosen-Ciphertext Security

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Cipher text-Policy Attribute-Based Proxy Re-Encryption (CP-ABPRE) extends the traditional Proxy Re-Encryption (PRE) by allowing a semi-trusted proxy to transform a cipher text under an access policy to the one with the same plaintext under another access policy (i.e. attribute-based re-encryption). The proxy, however, learns nothing about the underlying plaintext. CP-ABPRE has many real world applications, such as fine-grained access control in cloud storage systems and medical records sharing among different hospitals. Previous CP-ABPRE schemes leave how to be secure against Chosen-Cipher text Attacks (CCA) as an open problem. This paper, for the first time, proposes a new CP-ABPRE to tackle the problem. The new scheme supports attribute-based re-encryption with any monotonic access structures. Despite our scheme is constructed in the random oracle model, it can be proved CCA secure under the decisional q-parallel bilinear Diffie-Hellman exponent assumption.
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paper_title: Identity-based cryptosystems and signature schemes

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In this paper we introduce a novel type of cryptographic scheme, which enables any pair of users to communicate securely and to verify each other’s signatures without exchanging private or public keys, without keeping key directories, and without using the services of a third party. The scheme assumes the existence of trusted key generation centers, whose sole purpose is to give each user a personalized smart card when he first joins the network. The information embedded in this card enables the user to sign and encrypt the messages he sends and to decrypt and verify the messages he receives in a totally independent way, regardless of the identity of the other party. Previously issued cards do not have to be updated when new users join the network, and the various centers do not have to coordinate their activities or even to keep a user list. The centers can be closed after all the cards are issued, and the network can continue to function in a completely decentralized way for an indefinite period.
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paper_title: Enforcing Access Control in Virtual Organizations Using Hierarchical Attribute-Based Encryption

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Virtual organizations are dynamic, interorganizationalcollaborations that involve systems and servicesbelonging to different security domains. Several solutions havebeen proposed to guarantee the enforcement of the accesscontrol policies protecting the information exchanged in adistributed system, but none of them addresses the dynamicitycharacterizing virtual organizations. In this paper we proposea dynamic hierarchical attribute-based encryption (D-HABE)scheme that allows the institutions in a virtual organizationto encrypt information according to a policy in such a waythat only users with appropriate attributes can decrypt it. In addition, we introduce a key management scheme thatdetermines which user is entitled to receive which attributekey from which domain authority.
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paper_title: Hierarchical attribute-based encryption for fine-grained access control in cloud storage services

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Cloud computing, as an emerging computing paradigm, enables users to remotely store their data into a cloud so as to enjoy scalable services on-demand. Especially for small and medium-sized enterprises with limited budgets, they can achieve cost savings and productivity enhancements by using cloud-based services to manage projects, to make collaborations, and the like. However, allowing cloud service providers (CSPs), which are not in the same trusted domains as enterprise users, to take care of confidential data, may raise potential security and privacy issues. To keep the sensitive user data confidential against untrusted CSPs, a natural way is to apply cryptographic approaches, by disclosing decryption keys only to authorized users. However, when enterprise users outsource confidential data for sharing on cloud servers, the adopted encryption system should not only support fine-grained access control, but also provide high performance, full delegation, and scalability, so as to best serve the needs of accessing data anytime and anywhere, delegating within enterprises, and achieving a dynamic set of users. In this paper, we propose a scheme to help enterprises to efficiently share confidential data on cloud servers. We achieve this goal by first combining the hierarchical identity-based encryption (HIBE) system and the ciphertext-policy attribute-based encryption (CP-ABE) system, and then making a performance-expressivity tradeoff, finally applying proxy re-encryption and lazy re-encryption to our scheme.
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paper_title: Hierarchical attribute-set based encryption for scalable, flexible and fine-grained access control in cloud computing

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Cloud computing has emerged as the most influential paradigm in recent years. The new computing technology requires users to entrust their data to the cloud provider, which leads to security issues on the outsourced data. In order to achieve scalable, fine-grained and flexible access control for cloud computing, we extends Ciphertext-Policy Attribute-Set-Based Encryption (CP-ASBE) by building in a hierarchical structure to obtain Hierarchical Attribute-Set-Based Encryption (HASBE) for cloud computing. The proposed scheme inherits flexibility in supporting compound attributes, and achieves scalability due to the hierarchical structure. More efficient user revocation is achieved because of the use of attribute-set which allows us incrementally update user's expiration time. We analyze the proposed scheme, and it is showed that the scheme is not only efficient and flexible in dealing with access control for cloud computing, but also has the same security as CP-ASBE.
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paper_title: New ciphertext-policy attribute-based access control with efficient revocation

paper_content:

Attribute-Based Encryption (ABE) is one of the promising cryptographic primitives for fine-grained access control of shared outsourced data in cloud computing. However, before ABE can be deployed in data outsourcing systems, it has to provide efficient enforcement of authorization policies and policy updates. However, in order to tackle this issue, efficient and secure attribute and user revocation should be supported in original ABE scheme, which is still a challenge in existing work. In this paper, we propose a new ciphertext-policy ABE (CP-ABE) construction with efficient attribute and user revocation. Besides, an efficient access control mechanism is given based on the CP-ABE construction with an outsourcing computation service provider.
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paper_title: Decentralizing attribute-based encryption

paper_content:

We propose a Multi-Authority Attribute-Based Encryption (ABE) system. In our system, any party can become an authority and there is no requirement for any global coordination other than the creation of an initial set of common reference parameters. A party can simply act as an ABE authority by creating a public key and issuing private keys to different users that reflect their attributes. A user can encrypt data in terms of any boolean formula over attributes issued from any chosen set of authorities. Finally, our system does not require any central authority. ::: ::: In constructing our system, our largest technical hurdle is to make it collusion resistant. Prior Attribute-Based Encryption systems achieved collusion resistance when the ABE system authority "tied" together different components (representing different attributes) of a user's private key by randomizing the key. However, in our system each component will come from a potentially different authority, where we assume no coordination between such authorities. We create new techniques to tie key components together and prevent collusion attacks between users with different global identifiers. ::: ::: We prove our system secure using the recent dual system encryption methodology where the security proof works by first converting the challenge ciphertext and private keys to a semi-functional form and then arguing security. We follow a recent variant of the dual system proof technique due to Lewko and Waters and build our system using bilinear groups of composite order. We prove security under similar static assumptions to the LW paper in the random oracle model.
---
paper_title: Ciphertext-Policy Attribute-Based Encryption

paper_content:

In several distributed systems a user should only be able to access data if a user posses a certain set of credentials or attributes. Currently, the only method for enforcing such policies is to employ a trusted server to store the data and mediate access control. However, if any server storing the data is compromised, then the confidentiality of the data will be compromised. In this paper we present a system for realizing complex access control on encrypted data that we call ciphertext-policy attribute-based encryption. By using our techniques encrypted data can be kept confidential even if the storage server is untrusted; moreover, our methods are secure against collusion attacks. Previous attribute-based encryption systems used attributes to describe the encrypted data and built policies into user's keys; while in our system attributes are used to describe a user's credentials, and a party encrypting data determines a policy for who can decrypt. Thus, our methods are conceptually closer to traditional access control methods such as role-based access control (RBAC). In addition, we provide an implementation of our system and give performance measurements.
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paper_title: Conjunctive Broadcast and Attribute-Based Encryption

paper_content:

Attribute-based encryption (ABE) system enables an access control mechanism over encrypted data by specifying access policies among private keys and ciphertexts. There are two flavors of ABE, namely key-policy and ciphertext-policy, depending on which of private keys or ciphertexts that access policies are associated with. In this paper we propose a new cryptosystem called Broadcast ABE for both flavors. Broadcast ABE can be used to construct ABE systems with direct revocation mechanism. Direct revocation has a useful property that revocation can be done without affecting any non-revoked users; in particular, it does not require users to update keys periodically. For key-policy variant, our systems appear to be the first fully-functional directly revocable schemes. For ciphertext-policy variant, our systems improve the efficiency from the previously best revocable schemes; in particular, one of our schemes admits ciphertext and private key sizes roughly the same as the currently best (non-revocable) ciphertext-policy ABE. Broadcast ABE can also be utilized to construct multi-authority ABE in the disjunctive setting.
---
paper_title: Revocation Systems with Very Small Private Keys

paper_content:

In this work, we design a method for creating public key broadcast encryption systems. Our main technical innovation is based on a new "two equation" technique for revoking users. This technique results in two key contributions: First, our new scheme has ciphertext size overhead $O(r)$, where $r$ is the number of revoked users, and the size of public and private keys is only a \emph{constant} number of group elements from an elliptic-curve group of prime order. In addition, the public key allows us to encrypt to an unbounded number of users. Our system is the first to achieve such parameters. We give two versions of our scheme: a simpler version which we prove to be selectively secure in the standard model under a new, but non-interactive assumption, and another version that employs the new dual system encryption technique of Waters to obtain adaptive security under the d-BDH and decisional Linear assumptions. Second, we show that our techniques can be used to realize Attribute-Based Encryption (ABE) systems with non-monotonic access formulas, where our key storage is significantly more efficient than previous solutions. This result is also proven selectively secure in the standard model under our new non-interactive assumption.
---
paper_title: Attribute based proxy re-encryption with delegating capabilities

paper_content:

Attribute based proxy re-encryption scheme (ABPRE) is a new cryptographic primitive which extends the traditional proxy re-encryption (public key or identity based cryptosystem) to the attribute based counterpart, and thus empower users with delegating capability in the access control environment. Users, identified by attributes, could freely designate a proxy who can re-encrypt a ciphertext related with a certain access policy to another one with a different access policy. The proposed scheme is proved selective-structure chosen plaintext secure and master key secure without random oracles. Besides, we develop another kind of key delegating capability in our scheme and also discuss some related issues including a stronger security model and applications.
---
paper_title: A ciphertext policy attribute-based encryption scheme without pairings

paper_content:

Sahai and Waters [34] proposed Attribute-Based Encryption (ABE) as a new paradigm of encryption algorithms that allow the sender to set a policy to describe who can read the secret data. In recent years, lots of attribute-based schemes appeared in literatures, but almost all the schemes, to the best of our knowledge, are constructed from pairings. In this work, we present a ciphertext policy attribute-based encryption (CP-ABE) scheme, which supports and-gates without pairings. Our scheme is defined on q-ary lattices, and has a very strong security proof based on worst-case hardness. More precisely, under the learning with errors (LWE) assumption, our CP-ABE scheme is secure against chosen plaintext attack in the selective access structure model. Though our scheme only encrypts one bit at a time, we point out that it can support multi-bit encryption by using a well-known technique. Besides, our result can be easily extended to ideal lattices for a better efficiency.
---
paper_title: Attribute-based Proxy Re-encryption with a Constant Number of Pairing Operations

paper_content:

Attribute-based encryption (ABE) is an encryption scheme in which the user is able to decrypt a ciphertext with associated attributes. However, the scheme does not offer the capability of decryption to others when the user is offline. For this reason, the attribute-based proxy re-encryption (ABPRE) scheme was proposed, which combines traditional proxy re-encryption with ABE, so a user is able to empower designated users to decrypt the re-encrypted ciphertext with the associated attributes of designated users. However, previous ABPRE schemes demands a number of pairing operations that imply huge computational overhead. To reduce the number of pairing operations, we reduce the pairing operations with exponent operations. This paper provides a novel approach to an ABPRE scheme with constant pairing operation latency.
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paper_title: Privacy-aware Attribute-based Encryption with User Accountability

paper_content:

As a new public key primitive, attribute-based encryption (ABE) is envisioned to be a promising tool for implementing fine-grained access control. To further address the concern of user access privacy, privacy-aware ABE schemes are being developed to achieve hidden access policy recently. For the purpose of secure access control, there is, however, still one critical functionality missing in the existing ABE schemes, which is user accountability. Currently, no ABE scheme can completely prevent the problem of illegal key sharing among users. In this paper, we tackle this problem by firstly proposing the notion of accountable, anonymous, and ciphertext-policy ABE (CP-A3BE, in short) and then giving out a concrete construction. We start by improving the state-of-the-art of anonymous CP-ABE to obtain shorter public parameters and ciphertext length. In the proposed CP-A3BE construction, user accountability can be achieved in black-box model by embedding additional user-specific information into the attribute private key issued to that user, while still maintaining hidden access policy. The proposed constructions are provably secure.
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paper_title: Attribute-based encryption with non-monotonic access structures

paper_content:

We construct an Attribute-Based Encryption (ABE) scheme that allows a user's private key to be expressed in terms of any access formula over attributes. Previous ABE schemes were limited to expressing only monotonic access structures. We provide a proof of security for our scheme based on the Decisional Bilinear Diffie-Hellman (BDH) assumption. Furthermore, the performance of our new scheme compares favorably with existing, less-expressive schemes.
---
paper_title: Mediated Ciphertext-Policy Attribute-Based Encryption and Its Application

paper_content:

In Ciphertext-Policy Attribute-Based Encryption (CP-ABE), a user secret key is associated with a set of attributes, and the ciphertext is associated with an access policy over attributes. The user can decrypt the ciphertext if and only if the attribute set of his secret key satisfies the access policy specified in the ciphertext. Several CP-ABE schemes have been proposed, however, some practical problems, such as attribute revocation, still needs to be addressed. In this paper, we propose a mediated Ciphertext-Policy Attribute-Based Encryption (mCP-ABE) which extends CP-ABE with instantaneous attribute revocation. Furthermore, we demonstrate how to apply the proposed mCP-ABE scheme to securely manage Personal Health Records (PHRs).
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paper_title: Fully Secure Functional Encryption: Attribute-Based Encryption and (Hierarchical) Inner Product Encryption

paper_content:

We present two fully secure functional encryption schemes: a fully secure attribute-based encryption (ABE) scheme and a fully secure (attribute-hiding) predicate encryption (PE) scheme for inner-product predicates. In both cases, previous constructions were only proven to be selectively secure. Both results use novel strategies to adapt the dual system encryption methodology introduced by Waters. We construct our ABE scheme in composite order bilinear groups, and prove its security from three static assumptions. Our ABE scheme supports arbitrary monotone access formulas. Our predicate encryption scheme is constructed via a new approach on bilinear pairings using the notion of dual pairing vector spaces proposed by Okamoto and Takashima.
---
paper_title: nMIBAS: A Novel Multi-Receiver ID-Based Anonymous Signcryption with Decryption Fairness

paper_content:

Based on the ring signature technology, the multi-receiver ID-based anonymous signcryption (MIBAS) is proposed, and its goal is to protect the privacy of the sender or so-called signer. In an MIBAS scheme, every receiver can verify whether the sender is a member of a trusted group and thus ensure the reliability of the message source, but he could not get the real sender. However, MIBAS paid no attention to privacy of the receivers and has not taken the privacy of the receivers into account during its design. Our analyses show that there widely exist the receiver privacy exposure and decryption unfairness problems in the existing multi-receiver ID-based signcryption schemes. Motivated by these concerns, a new multi-receiver ID-based anonymous signcryption (nMIBAS) is proposed to protect the identity of the receivers. The nMIBAS scheme can not only solve the problem that the existing schemes cannot protect the privacy of receivers, but also meet the fairness of decryption to prevent the possible cheating behavior of the sender effectively. Analysis shows that this scheme is a secure and effective signcryption scheme.
---
paper_title: Efficient and Provable Secure Ciphertext-Policy Attribute-Based Encryption Schemes

paper_content:

In a ciphertext-policy attribute-based encryption (CP-ABE) scheme, the data is encrypted under an access policy defined by a user who encrypts the data and a user secret key is associated with a set of attributes which identify the user. A user can decrypt the ciphertext if and only if his attributes satisfy the access policy. In CP-ABE, since the user enforces the access policy at the encryption phase, the policy moves with the encrypted data. This is important for data storage servers where data confidentiality must be preserved even if the server is compromised or un-trusted. In this paper, we provide an efficient CP-ABE scheme which can express any access policy represented by a formula involving $\wedge$ and $\vee$ boolean operators. The scheme is secure under Decision Bilinear Diffie-Hellman assumption (DBDH). Furthermore, we extend the expressivity of the scheme by including \emph{of} (threshold) operator in addition to $\wedge$ and $\vee$ operators. We provide a comparison with existing CP-ABE schemes and show that our schemes are more efficient. Especially, the computational work done by the decryptor is reduced.
---
paper_title: Accountable authority key policy attribute-based encryption

paper_content:

We present an accountable authority key policy attribute-based encryption (A-KPABE) scheme. In this paper, we extend Goyal’s work to key policy attribute-based encryption setting. We first generalize the notion of accountable authority in key policy attribute-based encryption scenario, and then give a construction. In addition, our scheme is shown to be secure in the standard model under the modified Bilinear Decisional Diffie-Hellman (mBDDH) assumption.
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paper_title: Identity-based cryptosystems and signature schemes

paper_content:

In this paper we introduce a novel type of cryptographic scheme, which enables any pair of users to communicate securely and to verify each other’s signatures without exchanging private or public keys, without keeping key directories, and without using the services of a third party. The scheme assumes the existence of trusted key generation centers, whose sole purpose is to give each user a personalized smart card when he first joins the network. The information embedded in this card enables the user to sign and encrypt the messages he sends and to decrypt and verify the messages he receives in a totally independent way, regardless of the identity of the other party. Previously issued cards do not have to be updated when new users join the network, and the various centers do not have to coordinate their activities or even to keep a user list. The centers can be closed after all the cards are issued, and the network can continue to function in a completely decentralized way for an indefinite period.
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paper_title: Secure distributed key generation for discrete-log based cryptosystems

paper_content:

Distributed key generation is a main component of threshold cryptosystems and distributed cryptographic computing in general. Solutions to the distributed generation of private keys for discrete-log based cryptosystems have been known for several years and used in a variety of protocols and in many research papers. However, these solutions fail to provide the full security required and claimed by these works. We show how an active attacker controlling a small number of parties can bias the values of the generated keys, thus violating basic correctness and secrecy requirements of a key generation protocol. In particular, our attacks point out to the places where the proofs of security fail. Based on these findings we designed a distributed key generation protocol which we present here together with a rigorous proof of security. Our solution, that achieves optimal resiliency, can be used as a drop-in replacement for key generation modules as well as other components of threshold or proactive discrete-log based cryptosystems.
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paper_title: Attribute-based encryption for fine-grained access control of encrypted data

paper_content:

As more sensitive data is shared and stored by third-party sites on the Internet, there will be a need to encrypt data stored at these sites. One drawback of encrypting data, is that it can be selectively shared only at a coarse-grained level (i.e., giving another party your private key). We develop a new cryptosystem for fine-grained sharing of encrypted data that we call Key-Policy Attribute-Based Encryption (KP-ABE). In our cryptosystem, ciphertexts are labeled with sets of attributes and private keys are associated with access structures that control which ciphertexts a user is able to decrypt. We demonstrate the applicability of our construction to sharing of audit-log information and broadcast encryption. Our construction supports delegation of private keys which subsumesHierarchical Identity-Based Encryption (HIBE).
---
paper_title: Identity-based cryptosystems and signature schemes

paper_content:

In this paper we introduce a novel type of cryptographic scheme, which enables any pair of users to communicate securely and to verify each other’s signatures without exchanging private or public keys, without keeping key directories, and without using the services of a third party. The scheme assumes the existence of trusted key generation centers, whose sole purpose is to give each user a personalized smart card when he first joins the network. The information embedded in this card enables the user to sign and encrypt the messages he sends and to decrypt and verify the messages he receives in a totally independent way, regardless of the identity of the other party. Previously issued cards do not have to be updated when new users join the network, and the various centers do not have to coordinate their activities or even to keep a user list. The centers can be closed after all the cards are issued, and the network can continue to function in a completely decentralized way for an indefinite period.
---
paper_title: Attribute-based encryption for fine-grained access control of encrypted data

paper_content:

As more sensitive data is shared and stored by third-party sites on the Internet, there will be a need to encrypt data stored at these sites. One drawback of encrypting data, is that it can be selectively shared only at a coarse-grained level (i.e., giving another party your private key). We develop a new cryptosystem for fine-grained sharing of encrypted data that we call Key-Policy Attribute-Based Encryption (KP-ABE). In our cryptosystem, ciphertexts are labeled with sets of attributes and private keys are associated with access structures that control which ciphertexts a user is able to decrypt. We demonstrate the applicability of our construction to sharing of audit-log information and broadcast encryption. Our construction supports delegation of private keys which subsumesHierarchical Identity-Based Encryption (HIBE).
---
paper_title: Revocation Systems with Very Small Private Keys

paper_content:

In this work, we design a method for creating public key broadcast encryption systems. Our main technical innovation is based on a new "two equation" technique for revoking users. This technique results in two key contributions: First, our new scheme has ciphertext size overhead $O(r)$, where $r$ is the number of revoked users, and the size of public and private keys is only a \emph{constant} number of group elements from an elliptic-curve group of prime order. In addition, the public key allows us to encrypt to an unbounded number of users. Our system is the first to achieve such parameters. We give two versions of our scheme: a simpler version which we prove to be selectively secure in the standard model under a new, but non-interactive assumption, and another version that employs the new dual system encryption technique of Waters to obtain adaptive security under the d-BDH and decisional Linear assumptions. Second, we show that our techniques can be used to realize Attribute-Based Encryption (ABE) systems with non-monotonic access formulas, where our key storage is significantly more efficient than previous solutions. This result is also proven selectively secure in the standard model under our new non-interactive assumption.
---
paper_title: Attribute-based encryption with non-monotonic access structures

paper_content:

We construct an Attribute-Based Encryption (ABE) scheme that allows a user's private key to be expressed in terms of any access formula over attributes. Previous ABE schemes were limited to expressing only monotonic access structures. We provide a proof of security for our scheme based on the Decisional Bilinear Diffie-Hellman (BDH) assumption. Furthermore, the performance of our new scheme compares favorably with existing, less-expressive schemes.
---
paper_title: A ciphertext-policy attribute-based encryption scheme with constant ciphertext length

paper_content:

An Attribute-Based Encryption (ABE) is an encryption scheme where users with some attributes can decrypt ciphertexts associated with these attributes. The length of the ciphertext depends on the number of attributes in previous ABE schemes. In this paper, we propose a new Ciphertext-Policy Attribute-Based Encryption (CP-ABE) with constant ciphertext length. In our scheme, the number of pairing computations is also constant. In addition, the number of additional bits required from chosen plaintext attack-secure CP-ABE to chosen ciphertext attack-secure CP-ABE is reduced by 90% with respect to that of the previous scheme.
---
paper_title: Provably secure ciphertext policy ABE

paper_content:

In ciphertext policy attribute-based encryption (CP-ABE), every secret key is associated with a set of attributes, and every ciphertext is associated with an access structure on attributes. Decryption is enabled if and only if the user's attribute set satisfies the ciphertext access structure. This provides fine-grained access control on shared data in many practical settings, e.g., secure database and IP multicast. In this paper, we study CP-ABE schemes in which access structures are AND gates on positive and negative attributes. Our basic scheme is proven to be chosen plaintext (CPA) secure under the decisional bilinear Diffie-Hellman (DBDH) assumption. We then apply the Canetti-Halevi-Katz technique to obtain a chosen ciphertext (CCA) secure extension using one-time signatures. The security proof is a reduction to the DBDH assumption and the strong existential unforgeability of the signature primitive. In addition, we introduce hierarchical attributes to optimize our basic scheme - reducing both ciphertext size and encryption/decryption time while maintaining CPA security. We conclude with a discussion of practical applications of CP-ABE.
---
paper_title: Dual-Policy Attribute Based Encryption

paper_content:

We present a new variant of Attribute based encryption (ABE) called Dual-Policy ABE. Basically, it is a conjunctively combined scheme between Key-Policy and Ciphertext-Policy ABE, the two previous available types of ABE. Dual-Policy ABE allows simultaneously two access control mechanisms over encrypted data: one involves policies over objective attributes ascribed to data and the other involves policies over subjective attributes ascribed to user credentials. The previous two types of ABE can only allow either functionality above one at a time.
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paper_title: Attribute-based encryption with partially hidden encryptor-specified access structures

paper_content:

We propose attribute-based encryption schemes where encryptor-specified access structures (also called ciphertext policies) are hidden. By using our schemes, an encryptor can encrypt data with a hidden access structure. A decryptor obtains her secret key associated with her attributes from a trusted authority in advance and if the attributes associated with the decryptor's secret key do not satisfy the access structure associated with the encrypted data, the decryptor cannot decrypt the data or guess even what access structure was specified by the encryptor. We prove security of our construction based on the Decisional Bilinear Diffie-Hellman assumption and the Decision Linear assumption. In our security notion, even the legitimate decryptor cannot obtain the information about the access structure associated with the encrypted data more than the fact that she can decrypt the data.
---
paper_title: Attribute-based encryption for fine-grained access control of encrypted data

paper_content:

As more sensitive data is shared and stored by third-party sites on the Internet, there will be a need to encrypt data stored at these sites. One drawback of encrypting data, is that it can be selectively shared only at a coarse-grained level (i.e., giving another party your private key). We develop a new cryptosystem for fine-grained sharing of encrypted data that we call Key-Policy Attribute-Based Encryption (KP-ABE). In our cryptosystem, ciphertexts are labeled with sets of attributes and private keys are associated with access structures that control which ciphertexts a user is able to decrypt. We demonstrate the applicability of our construction to sharing of audit-log information and broadcast encryption. Our construction supports delegation of private keys which subsumesHierarchical Identity-Based Encryption (HIBE).
---
paper_title: Ciphertext-policy attribute-based encryption: an expressive, efficient, and provably secure realization

paper_content:

We present a new methodology for realizing Ciphertext-Policy Attribute Encryption (CP-ABE) under concrete and noninteractive cryptographic assumptions in the standard model. Our solutions allow any encryptor to specify access control in terms of any access formula over the attributes in the system. In our most efficient system, ciphertext size, encryption, and decryption time scales linearly with the complexity of the access formula. The only previous work to achieve these parameters was limited to a proof in the generic group model. ::: ::: We present three constructions within our framework. Our first system is proven selectively secure under a assumption that we call the decisional Parallel Bilinear Diffie-Hellman Exponent (PBDHE) assumption which can be viewed as a generalization of the BDHE assumption. Our next two constructions provide performance tradeoffs to achieve provable security respectively under the (weaker) decisional Bilinear-Diffie-Hellman Exponent and decisional Bilinear Diffie-Hellman assumptions.
---
paper_title: Bounded Ciphertext policy attribute based encryption

paper_content:

In a ciphertext policy attribute based encryption system, a user's private key is associated with a set of attributes (describing the user) and an encrypted ciphertext will specify an access policy over attributes. A user will be able to decrypt if and only if his attributes satisfy the ciphertext's policy. ::: ::: In this work, we present the first construction of a ciphertext-policy attribute based encryption scheme having a security proof based on a number theoretic assumption and supporting advanced access structures. Previous CP-ABE systems could either support only very limited access structures or had a proof of security only in the generic group model. Our construction can support access structures which can be represented by a bounded size access tree with threshold gates as its nodes. The bound on the size of the access trees is chosen at the time of the system setup. Our security proof is based on the standard Decisional Bilinear Diffie-Hellman assumption.
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paper_title: Provably secure and efficient bounded ciphertext policy attribute based encryption

paper_content:

Ciphertext policy attribute based encryption (CPABE) allows a sender to distribute messages based on an access policy which can be expressed as a boolean function consisting of (OR, AND) gates between attributes. A receiver whose secret key is associated with those attributes could only decrypt a ciphertext successfully if and only if his attributes satisfy the ciphertext's access policy. Fine-grained access control, a new concept mentioned by GPSW in CCS'06 can realize a more delicate access policy which could be represented as an access tree with threshold gates connecting attributes. In ICALP'08, Goyal et al. design a bounded CPABE (denoted as GJPS) with fine-grained access policy which can be proven secure under a number-theoretic assumption. In this paper, we improve their scheme by providing faster encryption / decryption algorithm and shortened ciphertext size. Moreover, we use one-time signature technique to obtain a chosen ciphertext secure extension and give its complete security proof in the standard model under traditional Decisional Bilinear Diffie-Hellman (DBDH) assumption and strong existential unforgeability of one-time signature scheme.
---
paper_title: Ciphertext-Policy Attribute-Based Encryption

paper_content:

In several distributed systems a user should only be able to access data if a user posses a certain set of credentials or attributes. Currently, the only method for enforcing such policies is to employ a trusted server to store the data and mediate access control. However, if any server storing the data is compromised, then the confidentiality of the data will be compromised. In this paper we present a system for realizing complex access control on encrypted data that we call ciphertext-policy attribute-based encryption. By using our techniques encrypted data can be kept confidential even if the storage server is untrusted; moreover, our methods are secure against collusion attacks. Previous attribute-based encryption systems used attributes to describe the encrypted data and built policies into user's keys; while in our system attributes are used to describe a user's credentials, and a party encrypting data determines a policy for who can decrypt. Thus, our methods are conceptually closer to traditional access control methods such as role-based access control (RBAC). In addition, we provide an implementation of our system and give performance measurements.
---
paper_title: A ciphertext policy attribute-based encryption scheme without pairings

paper_content:

Sahai and Waters [34] proposed Attribute-Based Encryption (ABE) as a new paradigm of encryption algorithms that allow the sender to set a policy to describe who can read the secret data. In recent years, lots of attribute-based schemes appeared in literatures, but almost all the schemes, to the best of our knowledge, are constructed from pairings. In this work, we present a ciphertext policy attribute-based encryption (CP-ABE) scheme, which supports and-gates without pairings. Our scheme is defined on q-ary lattices, and has a very strong security proof based on worst-case hardness. More precisely, under the learning with errors (LWE) assumption, our CP-ABE scheme is secure against chosen plaintext attack in the selective access structure model. Though our scheme only encrypts one bit at a time, we point out that it can support multi-bit encryption by using a well-known technique. Besides, our result can be easily extended to ideal lattices for a better efficiency.
---
paper_title: Fully Secure Functional Encryption: Attribute-Based Encryption and (Hierarchical) Inner Product Encryption

paper_content:

We present two fully secure functional encryption schemes: a fully secure attribute-based encryption (ABE) scheme and a fully secure (attribute-hiding) predicate encryption (PE) scheme for inner-product predicates. In both cases, previous constructions were only proven to be selectively secure. Both results use novel strategies to adapt the dual system encryption methodology introduced by Waters. We construct our ABE scheme in composite order bilinear groups, and prove its security from three static assumptions. Our ABE scheme supports arbitrary monotone access formulas. Our predicate encryption scheme is constructed via a new approach on bilinear pairings using the notion of dual pairing vector spaces proposed by Okamoto and Takashima.
---
paper_title: Efficient and Provable Secure Ciphertext-Policy Attribute-Based Encryption Schemes

paper_content:

In a ciphertext-policy attribute-based encryption (CP-ABE) scheme, the data is encrypted under an access policy defined by a user who encrypts the data and a user secret key is associated with a set of attributes which identify the user. A user can decrypt the ciphertext if and only if his attributes satisfy the access policy. In CP-ABE, since the user enforces the access policy at the encryption phase, the policy moves with the encrypted data. This is important for data storage servers where data confidentiality must be preserved even if the server is compromised or un-trusted. In this paper, we provide an efficient CP-ABE scheme which can express any access policy represented by a formula involving $\wedge$ and $\vee$ boolean operators. The scheme is secure under Decision Bilinear Diffie-Hellman assumption (DBDH). Furthermore, we extend the expressivity of the scheme by including \emph{of} (threshold) operator in addition to $\wedge$ and $\vee$ operators. We provide a comparison with existing CP-ABE schemes and show that our schemes are more efficient. Especially, the computational work done by the decryptor is reduced.
---
paper_title: A ciphertext-policy attribute-based encryption scheme with constant ciphertext length

paper_content:

An Attribute-Based Encryption (ABE) is an encryption scheme where users with some attributes can decrypt ciphertexts associated with these attributes. The length of the ciphertext depends on the number of attributes in previous ABE schemes. In this paper, we propose a new Ciphertext-Policy Attribute-Based Encryption (CP-ABE) with constant ciphertext length. In our scheme, the number of pairing computations is also constant. In addition, the number of additional bits required from chosen plaintext attack-secure CP-ABE to chosen ciphertext attack-secure CP-ABE is reduced by 90% with respect to that of the previous scheme.
---
paper_title: Attribute-based encryption for fine-grained access control of encrypted data

paper_content:

As more sensitive data is shared and stored by third-party sites on the Internet, there will be a need to encrypt data stored at these sites. One drawback of encrypting data, is that it can be selectively shared only at a coarse-grained level (i.e., giving another party your private key). We develop a new cryptosystem for fine-grained sharing of encrypted data that we call Key-Policy Attribute-Based Encryption (KP-ABE). In our cryptosystem, ciphertexts are labeled with sets of attributes and private keys are associated with access structures that control which ciphertexts a user is able to decrypt. We demonstrate the applicability of our construction to sharing of audit-log information and broadcast encryption. Our construction supports delegation of private keys which subsumesHierarchical Identity-Based Encryption (HIBE).
---
paper_title: Ciphertext-policy attribute-based encryption: an expressive, efficient, and provably secure realization

paper_content:

We present a new methodology for realizing Ciphertext-Policy Attribute Encryption (CP-ABE) under concrete and noninteractive cryptographic assumptions in the standard model. Our solutions allow any encryptor to specify access control in terms of any access formula over the attributes in the system. In our most efficient system, ciphertext size, encryption, and decryption time scales linearly with the complexity of the access formula. The only previous work to achieve these parameters was limited to a proof in the generic group model. ::: ::: We present three constructions within our framework. Our first system is proven selectively secure under a assumption that we call the decisional Parallel Bilinear Diffie-Hellman Exponent (PBDHE) assumption which can be viewed as a generalization of the BDHE assumption. Our next two constructions provide performance tradeoffs to achieve provable security respectively under the (weaker) decisional Bilinear-Diffie-Hellman Exponent and decisional Bilinear Diffie-Hellman assumptions.
---
paper_title: Ciphertext-Policy Attribute-Based Encryption

paper_content:

In several distributed systems a user should only be able to access data if a user posses a certain set of credentials or attributes. Currently, the only method for enforcing such policies is to employ a trusted server to store the data and mediate access control. However, if any server storing the data is compromised, then the confidentiality of the data will be compromised. In this paper we present a system for realizing complex access control on encrypted data that we call ciphertext-policy attribute-based encryption. By using our techniques encrypted data can be kept confidential even if the storage server is untrusted; moreover, our methods are secure against collusion attacks. Previous attribute-based encryption systems used attributes to describe the encrypted data and built policies into user's keys; while in our system attributes are used to describe a user's credentials, and a party encrypting data determines a policy for who can decrypt. Thus, our methods are conceptually closer to traditional access control methods such as role-based access control (RBAC). In addition, we provide an implementation of our system and give performance measurements.
---
paper_title: Attribute-based encryption with non-monotonic access structures

paper_content:

We construct an Attribute-Based Encryption (ABE) scheme that allows a user's private key to be expressed in terms of any access formula over attributes. Previous ABE schemes were limited to expressing only monotonic access structures. We provide a proof of security for our scheme based on the Decisional Bilinear Diffie-Hellman (BDH) assumption. Furthermore, the performance of our new scheme compares favorably with existing, less-expressive schemes.
---
paper_title: Improving privacy and security in multi-authority attribute-based encryption

paper_content:

Attribute based encryption (ABE) [13] determines decryption ability based on a user's attributes. In a multi-authority ABE scheme, multiple attribute-authorities monitor different sets of attributes and issue corresponding decryption keys to users, and encryptors can require that a user obtain keys for appropriate attributes from each authority before decrypting a message. Chase [5] gave a multi-authority ABE scheme using the concepts of a trusted central authority (CA) and global identifiers (GID). However, the CA in that construction has the power to decrypt every ciphertext, which seems somehow contradictory to the original goal of distributing control over many potentially untrusted authorities. Moreover, in that construction, the use of a consistent GID allowed the authorities to combine their information to build a full profile with all of a user's attributes, which unnecessarily compromises the privacy of the user. In this paper, we propose a solution which removes the trusted central authority, and protects the users' privacy by preventing the authorities from pooling their information on particular users, thus making ABE more usable in practice.
---
paper_title: Fully secure multi-authority ciphertext-policy attribute-based encryption without random oracles

paper_content:

Recently Lewko and Waters proposed the first fully secure multi-authority ciphertext-policy attribute-based encryption (CP-ABE) system in the random oracle model, and leave the construction of a fully secure multi-authority CP-ABE in the standard model as an open problem. Also, there is no CP-ABE system which can completely prevent individual authorities from decrypting ciphertexts. In this paper, we propose a new multi-authority CP-ABE system which addresses these two problems positively. In this new system, there are multiple Central Authorities (CAs) and Attribute Authorities (AAs), the CAs issue identity-related keys to users and are not involved in any attribute related operations, AAs issue attribute-related keys to users and each AA manages a different domain of attributes. The AAs operate independently from each other and do not need to know the existence of other AAs. Messages can be encrypted under any monotone access structure over the entire attribute universe. The system is adaptively secure in the standard model with adaptive authority corruption, and can support large attribute universe.
---
paper_title: Multi-Authority Attribute Based Encryption

paper_content:

In an identity based encryption scheme, each user is identified by a unique identity string. An attribute based encryption scheme (ABE), in contrast, is a scheme in which each user is identified by a set of attributes, and some function of those attributes is used to determine decryption ability for each ciphertext. Sahai and Waters introduced a single authority attribute encryption scheme and left open the question of whether a scheme could be constructed in which multiple authorities were allowed to distribute attributes [SW05]. We answer this question in the affirmative. ::: ::: Our scheme allows any polynomial number of independent authorities to monitor attributes and distribute secret keys. An encryptor can choose, for each authority, a number dk and a set of attributes; he can then encrypt a message such that a user can only decrypt if he has at least dk of the given attributes from each authority k. Our scheme can tolerate an arbitrary number of corrupt authoritites. ::: ::: We also show how to apply our techniques to achieve a multiauthority version of the large universe fine grained access control ABE presented by Gopal et al. [GPSW06].
---
paper_title: Privacy-Preserving Decentralized Key-Policy Attribute-Based Encryption

paper_content:

Decentralized attribute-based encryption (ABE) is a variant of a multiauthority ABE scheme where each authority can issue secret keys to the user independently without any cooperation and a central authority. This is in contrast to the previous constructions, where multiple authorities must be online and setup the system interactively, which is impractical. Hence, it is clear that a decentralized ABE scheme eliminates the heavy communication cost and the need for collaborative computation in the setup stage. Furthermore, every authority can join or leave the system freely without the necessity of reinitializing the system. In contemporary multiauthority ABE schemes, a user's secret keys from different authorities must be tied to his global identifier (GID) to resist the collusion attack. However, this will compromise the user's privacy. Multiple authorities can collaborate to trace the user by his GID, collect his attributes, then impersonate him. Therefore, constructing a decentralized ABE scheme with privacy-preserving remains a challenging research problem. In this paper, we propose a privacy-preserving decentralized key-policy ABE scheme where each authority can issue secret keys to a user independently without knowing anything about his GID. Therefore, even if multiple authorities are corrupted, they cannot collect the user's attributes by tracing his GID. Notably, our scheme only requires standard complexity assumptions (e.g., decisional bilinear Diffie-Hellman) and does not require any cooperation between the multiple authorities, in contrast to the previous comparable scheme that requires nonstandard complexity assumptions (e.g., q-decisional Diffie-Hellman inversion) and interactions among multiple authorities. To the best of our knowledge, it is the first decentralized ABE scheme with privacy-preserving based on standard complexity assumptions.
---
paper_title: Multi-authority attribute-based encryption with honest-but-curious central authority

paper_content:

An attribute-based encryption scheme capable of handling multiple authorities was recently proposed by Chase. The scheme is built upon a single-authority attribute-based encryption scheme presented earlier by Sahai and Waters. Chase's construction uses a trusted central authority that is inherently capable of decrypting arbitrary ciphertexts created within the system. We present a multi-authority attribute-based encryption scheme in which only the set of recipients defined by the encrypting party can decrypt a corresponding ciphertext. The central authority is viewed as ‘honest-but-curious’: on the one hand, it honestly follows the protocol, and on the other hand, it is curious to decrypt arbitrary ciphertexts thus violating the intent of the encrypting party. The proposed scheme, which like its predecessors relies on the Bilinear Diffie–Hellman assumption, has a complexity comparable to that of Chase's scheme. We prove that our scheme is secure in the selective ID model and can tolerate an honest-but-curious central authority.
---
paper_title: Decentralizing attribute-based encryption

paper_content:

We propose a Multi-Authority Attribute-Based Encryption (ABE) system. In our system, any party can become an authority and there is no requirement for any global coordination other than the creation of an initial set of common reference parameters. A party can simply act as an ABE authority by creating a public key and issuing private keys to different users that reflect their attributes. A user can encrypt data in terms of any boolean formula over attributes issued from any chosen set of authorities. Finally, our system does not require any central authority. ::: ::: In constructing our system, our largest technical hurdle is to make it collusion resistant. Prior Attribute-Based Encryption systems achieved collusion resistance when the ABE system authority "tied" together different components (representing different attributes) of a user's private key by randomizing the key. However, in our system each component will come from a potentially different authority, where we assume no coordination between such authorities. We create new techniques to tie key components together and prevent collusion attacks between users with different global identifiers. ::: ::: We prove our system secure using the recent dual system encryption methodology where the security proof works by first converting the challenge ciphertext and private keys to a semi-functional form and then arguing security. We follow a recent variant of the dual system proof technique due to Lewko and Waters and build our system using bilinear groups of composite order. We prove security under similar static assumptions to the LW paper in the random oracle model.
---
paper_title: Fully secure multi-authority ciphertext-policy attribute-based encryption without random oracles

paper_content:

Recently Lewko and Waters proposed the first fully secure multi-authority ciphertext-policy attribute-based encryption (CP-ABE) system in the random oracle model, and leave the construction of a fully secure multi-authority CP-ABE in the standard model as an open problem. Also, there is no CP-ABE system which can completely prevent individual authorities from decrypting ciphertexts. In this paper, we propose a new multi-authority CP-ABE system which addresses these two problems positively. In this new system, there are multiple Central Authorities (CAs) and Attribute Authorities (AAs), the CAs issue identity-related keys to users and are not involved in any attribute related operations, AAs issue attribute-related keys to users and each AA manages a different domain of attributes. The AAs operate independently from each other and do not need to know the existence of other AAs. Messages can be encrypted under any monotone access structure over the entire attribute universe. The system is adaptively secure in the standard model with adaptive authority corruption, and can support large attribute universe.
---
paper_title: Multi-Authority Attribute Based Encryption

paper_content:

In an identity based encryption scheme, each user is identified by a unique identity string. An attribute based encryption scheme (ABE), in contrast, is a scheme in which each user is identified by a set of attributes, and some function of those attributes is used to determine decryption ability for each ciphertext. Sahai and Waters introduced a single authority attribute encryption scheme and left open the question of whether a scheme could be constructed in which multiple authorities were allowed to distribute attributes [SW05]. We answer this question in the affirmative. ::: ::: Our scheme allows any polynomial number of independent authorities to monitor attributes and distribute secret keys. An encryptor can choose, for each authority, a number dk and a set of attributes; he can then encrypt a message such that a user can only decrypt if he has at least dk of the given attributes from each authority k. Our scheme can tolerate an arbitrary number of corrupt authoritites. ::: ::: We also show how to apply our techniques to achieve a multiauthority version of the large universe fine grained access control ABE presented by Gopal et al. [GPSW06].
---
paper_title: Multi-authority attribute-based encryption with honest-but-curious central authority

paper_content:

An attribute-based encryption scheme capable of handling multiple authorities was recently proposed by Chase. The scheme is built upon a single-authority attribute-based encryption scheme presented earlier by Sahai and Waters. Chase's construction uses a trusted central authority that is inherently capable of decrypting arbitrary ciphertexts created within the system. We present a multi-authority attribute-based encryption scheme in which only the set of recipients defined by the encrypting party can decrypt a corresponding ciphertext. The central authority is viewed as ‘honest-but-curious’: on the one hand, it honestly follows the protocol, and on the other hand, it is curious to decrypt arbitrary ciphertexts thus violating the intent of the encrypting party. The proposed scheme, which like its predecessors relies on the Bilinear Diffie–Hellman assumption, has a complexity comparable to that of Chase's scheme. We prove that our scheme is secure in the selective ID model and can tolerate an honest-but-curious central authority.
---
paper_title: Fully Secure Functional Encryption: Attribute-Based Encryption and (Hierarchical) Inner Product Encryption

paper_content:

We present two fully secure functional encryption schemes: a fully secure attribute-based encryption (ABE) scheme and a fully secure (attribute-hiding) predicate encryption (PE) scheme for inner-product predicates. In both cases, previous constructions were only proven to be selectively secure. Both results use novel strategies to adapt the dual system encryption methodology introduced by Waters. We construct our ABE scheme in composite order bilinear groups, and prove its security from three static assumptions. Our ABE scheme supports arbitrary monotone access formulas. Our predicate encryption scheme is constructed via a new approach on bilinear pairings using the notion of dual pairing vector spaces proposed by Okamoto and Takashima.
---
paper_title: Improving privacy and security in multi-authority attribute-based encryption

paper_content:

Attribute based encryption (ABE) [13] determines decryption ability based on a user's attributes. In a multi-authority ABE scheme, multiple attribute-authorities monitor different sets of attributes and issue corresponding decryption keys to users, and encryptors can require that a user obtain keys for appropriate attributes from each authority before decrypting a message. Chase [5] gave a multi-authority ABE scheme using the concepts of a trusted central authority (CA) and global identifiers (GID). However, the CA in that construction has the power to decrypt every ciphertext, which seems somehow contradictory to the original goal of distributing control over many potentially untrusted authorities. Moreover, in that construction, the use of a consistent GID allowed the authorities to combine their information to build a full profile with all of a user's attributes, which unnecessarily compromises the privacy of the user. In this paper, we propose a solution which removes the trusted central authority, and protects the users' privacy by preventing the authorities from pooling their information on particular users, thus making ABE more usable in practice.
---
paper_title: Fully secure multi-authority ciphertext-policy attribute-based encryption without random oracles

paper_content:

Recently Lewko and Waters proposed the first fully secure multi-authority ciphertext-policy attribute-based encryption (CP-ABE) system in the random oracle model, and leave the construction of a fully secure multi-authority CP-ABE in the standard model as an open problem. Also, there is no CP-ABE system which can completely prevent individual authorities from decrypting ciphertexts. In this paper, we propose a new multi-authority CP-ABE system which addresses these two problems positively. In this new system, there are multiple Central Authorities (CAs) and Attribute Authorities (AAs), the CAs issue identity-related keys to users and are not involved in any attribute related operations, AAs issue attribute-related keys to users and each AA manages a different domain of attributes. The AAs operate independently from each other and do not need to know the existence of other AAs. Messages can be encrypted under any monotone access structure over the entire attribute universe. The system is adaptively secure in the standard model with adaptive authority corruption, and can support large attribute universe.
---
paper_title: Multi-Authority Attribute Based Encryption

paper_content:

In an identity based encryption scheme, each user is identified by a unique identity string. An attribute based encryption scheme (ABE), in contrast, is a scheme in which each user is identified by a set of attributes, and some function of those attributes is used to determine decryption ability for each ciphertext. Sahai and Waters introduced a single authority attribute encryption scheme and left open the question of whether a scheme could be constructed in which multiple authorities were allowed to distribute attributes [SW05]. We answer this question in the affirmative. ::: ::: Our scheme allows any polynomial number of independent authorities to monitor attributes and distribute secret keys. An encryptor can choose, for each authority, a number dk and a set of attributes; he can then encrypt a message such that a user can only decrypt if he has at least dk of the given attributes from each authority k. Our scheme can tolerate an arbitrary number of corrupt authoritites. ::: ::: We also show how to apply our techniques to achieve a multiauthority version of the large universe fine grained access control ABE presented by Gopal et al. [GPSW06].
---
paper_title: Robust threshold DSS signatures

paper_content:

We present threshold DSS (Digital Signature Standard) signatures where the power to sign is shared by n players such that for a given parameter t < n/2 any subset of 2t + 1 signers can collaborate to produce a valid DSS signature on any given message, but no subset of t corrupted players can forge a signature (in particular, cannot learn the signature key). In addition, we present a robust threshold DSS scheme that can also tolerate n/3 players who refuse to participate in the signature protocol. We can also endure n/4 maliciously faulty players that generate incorrect partial signatures at the time of signature computation. This results in a highly secure and resilient DSS signature system applicable to the protection of the secret signature key, the prevention of forgery, and increased system availability. ::: ::: Our results significantly improve over a recent result by Langford from CRYPTO'95 that presents threshold DSS signatures which can stand much smaller subsets of corrupted players, namely, t ≅ √n, and do not enjoy the robustness property. As in thc case of Langford's result, our schemes require no trusted party. Our techniques apply to other threshold ElGamal-like signatures as well. We prove the security of our schemes solely based on the hardness of forging a regular DSS signature.
---
paper_title: Privacy-Preserving Decentralized Key-Policy Attribute-Based Encryption

paper_content:

Decentralized attribute-based encryption (ABE) is a variant of a multiauthority ABE scheme where each authority can issue secret keys to the user independently without any cooperation and a central authority. This is in contrast to the previous constructions, where multiple authorities must be online and setup the system interactively, which is impractical. Hence, it is clear that a decentralized ABE scheme eliminates the heavy communication cost and the need for collaborative computation in the setup stage. Furthermore, every authority can join or leave the system freely without the necessity of reinitializing the system. In contemporary multiauthority ABE schemes, a user's secret keys from different authorities must be tied to his global identifier (GID) to resist the collusion attack. However, this will compromise the user's privacy. Multiple authorities can collaborate to trace the user by his GID, collect his attributes, then impersonate him. Therefore, constructing a decentralized ABE scheme with privacy-preserving remains a challenging research problem. In this paper, we propose a privacy-preserving decentralized key-policy ABE scheme where each authority can issue secret keys to a user independently without knowing anything about his GID. Therefore, even if multiple authorities are corrupted, they cannot collect the user's attributes by tracing his GID. Notably, our scheme only requires standard complexity assumptions (e.g., decisional bilinear Diffie-Hellman) and does not require any cooperation between the multiple authorities, in contrast to the previous comparable scheme that requires nonstandard complexity assumptions (e.g., q-decisional Diffie-Hellman inversion) and interactions among multiple authorities. To the best of our knowledge, it is the first decentralized ABE scheme with privacy-preserving based on standard complexity assumptions.
---
paper_title: Ciphertext-policy attribute-based encryption: an expressive, efficient, and provably secure realization

paper_content:

We present a new methodology for realizing Ciphertext-Policy Attribute Encryption (CP-ABE) under concrete and noninteractive cryptographic assumptions in the standard model. Our solutions allow any encryptor to specify access control in terms of any access formula over the attributes in the system. In our most efficient system, ciphertext size, encryption, and decryption time scales linearly with the complexity of the access formula. The only previous work to achieve these parameters was limited to a proof in the generic group model. ::: ::: We present three constructions within our framework. Our first system is proven selectively secure under a assumption that we call the decisional Parallel Bilinear Diffie-Hellman Exponent (PBDHE) assumption which can be viewed as a generalization of the BDHE assumption. Our next two constructions provide performance tradeoffs to achieve provable security respectively under the (weaker) decisional Bilinear-Diffie-Hellman Exponent and decisional Bilinear Diffie-Hellman assumptions.
---
paper_title: Decentralizing attribute-based encryption

paper_content:

We propose a Multi-Authority Attribute-Based Encryption (ABE) system. In our system, any party can become an authority and there is no requirement for any global coordination other than the creation of an initial set of common reference parameters. A party can simply act as an ABE authority by creating a public key and issuing private keys to different users that reflect their attributes. A user can encrypt data in terms of any boolean formula over attributes issued from any chosen set of authorities. Finally, our system does not require any central authority. ::: ::: In constructing our system, our largest technical hurdle is to make it collusion resistant. Prior Attribute-Based Encryption systems achieved collusion resistance when the ABE system authority "tied" together different components (representing different attributes) of a user's private key by randomizing the key. However, in our system each component will come from a potentially different authority, where we assume no coordination between such authorities. We create new techniques to tie key components together and prevent collusion attacks between users with different global identifiers. ::: ::: We prove our system secure using the recent dual system encryption methodology where the security proof works by first converting the challenge ciphertext and private keys to a semi-functional form and then arguing security. We follow a recent variant of the dual system proof technique due to Lewko and Waters and build our system using bilinear groups of composite order. We prove security under similar static assumptions to the LW paper in the random oracle model.
---
paper_title: Secure distributed key generation for discrete-log based cryptosystems

paper_content:

Distributed key generation is a main component of threshold cryptosystems and distributed cryptographic computing in general. Solutions to the distributed generation of private keys for discrete-log based cryptosystems have been known for several years and used in a variety of protocols and in many research papers. However, these solutions fail to provide the full security required and claimed by these works. We show how an active attacker controlling a small number of parties can bias the values of the generated keys, thus violating basic correctness and secrecy requirements of a key generation protocol. In particular, our attacks point out to the places where the proofs of security fail. Based on these findings we designed a distributed key generation protocol which we present here together with a rigorous proof of security. Our solution, that achieves optimal resiliency, can be used as a drop-in replacement for key generation modules as well as other components of threshold or proactive discrete-log based cryptosystems.
---
paper_title: Secure attribute-based systems

paper_content:

Attributes define, classify, or annotate the datum to which they are assigned. However, traditional attribute architectures and cryptosystems are ill-equipped to provide security in the face of diverse access requirements and environments. In this paper, we introduce a novel secure information management architecture based on emerging attribute-based encryption (ABE) primitives. A policy system that meets the needs of complex policies is defined and illustrated. Based on the needs of those policies, we propose cryptographic optimizations that vastly improve enforcement efficiency. We further explore the use of such policies in two example applications: a HIPAA compliant distributed file system and a social network. A performance analysis of our ABE system and example applications demonstrates the ability to reduce cryptographic costs by as much as 98% over previously proposed constructions. Through this, we demonstrate that our attribute system is an efficient solution for securely managing information in large, loosely-coupled, distributed systems.
---
paper_title: Attribute-Based Encryption Supporting Direct/Indirect Revocation Modes

paper_content:

Attribute-based encryption (ABE) enables an access control mechanism over encrypted data by specifying access policies among private keys and ciphertexts. In this paper, we focus on ABE that supports revocation. Currently, there are two available revocable ABE schemes in the literature. Their revocation mechanisms, however, differ in the sense that they can be considered as direct and indirect methods. Direct revocation enforces revocation directly by the sender who specifies the revocation list while encrypting. Indirect revocation enforces revocation by the key authority who releases a key update material periodically in such a way that only non-revoked users can update their keys (hence, revoked users' keys are implicitly rendered useless). An advantage of the indirect method over the direct one is that it does not require senders to know the revocation list. In contrast, an advantage of the direct method over the other is that it does not involve key update phase for all non-revoked users interacting with the key authority. In this paper, we present the first Hybrid Revocable ABE scheme that allows senders to select on-the-fly when encrypting whether to use either direct or indirect revocation mode; therefore, it combines best advantages from both methods.
---
paper_title: Attribute-Based Access Control with Efficient Revocation in Data Outsourcing Systems

paper_content:

Some of the most challenging issues in data outsourcing scenario are the enforcement of authorization policies and the support of policy updates. Ciphertext-policy attribute-based encryption is a promising cryptographic solution to these issues for enforcing access control policies defined by a data owner on outsourced data. However, the problem of applying the attribute-based encryption in an outsourced architecture introduces several challenges with regard to the attribute and user revocation. In this paper, we propose an access control mechanism using ciphertext-policy attribute-based encryption to enforce access control policies with efficient attribute and user revocation capability. The fine-grained access control can be achieved by dual encryption mechanism which takes advantage of the attribute-based encryption and selective group key distribution in each attribute group. We demonstrate how to apply the proposed mechanism to securely manage the outsourced data. The analysis results indicate that the proposed scheme is efficient and secure in the data outsourcing systems.
---
paper_title: Attribute based data sharing with attribute revocation

paper_content:

Ciphertext-Policy Attribute Based Encryption (CP-ABE) is a promising cryptographic primitive for fine-grained access control of shared data. In CP-ABE, each user is associated with a set of attributes and data are encrypted with access structures on attributes. A user is able to decrypt a ciphertext if and only if his attributes satisfy the ciphertext access structure. Beside this basic property, practical applications usually have other requirements. In this paper we focus on an important issue of attribute revocation which is cumbersome for CP-ABE schemes. In particular, we resolve this challenging issue by considering more practical scenarios in which semi-trustable on-line proxy servers are available. As compared to existing schemes, our proposed solution enables the authority to revoke user attributes with minimal effort. We achieve this by uniquely integrating the technique of proxy re-encryption with CP-ABE, and enable the authority to delegate most of laborious tasks to proxy servers. Formal analysis shows that our proposed scheme is provably secure against chosen ciphertext attacks. In addition, we show that our technique can also be applicable to the Key-Policy Attribute Based Encryption (KP-ABE) counterpart.
---
paper_title: Revocation and Tracing Schemes for Stateless Receivers

paper_content:

We deal with the problem of a center sending a message to a group of users such that some subset of the users is considered revoked and should not be able to obtain the content of the message. We concentrate on the stateless receiver case, where the users do not (necessarily) update their state from session to session. We present a framework called the Subset-Cover framework, which abstracts a variety of revocation schemes including some previously known ones. We provide sufficient conditions that guarantees the security of a revocation algorithm in this class. We describe two explicit Subset-Cover revocation algorithms; these algorithms are very flexible and work for any number of revoked users. The schemes require storage at the receiver of log N and 1/2 log 2 N keys respectively (N is the total number of users), and in order to revoke r users the required message lengths are of r log N and 2r keys respectively. We also provide a general traitor tracing mechanism that can be integrated with any Subset-Cover revocation scheme that satisfies a bifurcation property. This mechanism does not need an a priori bound on the number of traitors and does not expand the message length by much compared to the revocation of the same set of traitors. The main improvements of these methods over previously suggested methods, when adopted to the stateless scenario, are: (1) reducing the message length to O(r) regardless of the coalition size while maintaining a single decryption at the user's end (2) provide a seamless integration between the revocation and tracing so that the tracing mechanisms does not require any change to the revocation algorithm.
---
paper_title: New ciphertext-policy attribute-based access control with efficient revocation

paper_content:

Attribute-Based Encryption (ABE) is one of the promising cryptographic primitives for fine-grained access control of shared outsourced data in cloud computing. However, before ABE can be deployed in data outsourcing systems, it has to provide efficient enforcement of authorization policies and policy updates. However, in order to tackle this issue, efficient and secure attribute and user revocation should be supported in original ABE scheme, which is still a challenge in existing work. In this paper, we propose a new ciphertext-policy ABE (CP-ABE) construction with efficient attribute and user revocation. Besides, an efficient access control mechanism is given based on the CP-ABE construction with an outsourcing computation service provider.
---
paper_title: Ciphertext-Policy Attribute-Based Encryption

paper_content:

In several distributed systems a user should only be able to access data if a user posses a certain set of credentials or attributes. Currently, the only method for enforcing such policies is to employ a trusted server to store the data and mediate access control. However, if any server storing the data is compromised, then the confidentiality of the data will be compromised. In this paper we present a system for realizing complex access control on encrypted data that we call ciphertext-policy attribute-based encryption. By using our techniques encrypted data can be kept confidential even if the storage server is untrusted; moreover, our methods are secure against collusion attacks. Previous attribute-based encryption systems used attributes to describe the encrypted data and built policies into user's keys; while in our system attributes are used to describe a user's credentials, and a party encrypting data determines a policy for who can decrypt. Thus, our methods are conceptually closer to traditional access control methods such as role-based access control (RBAC). In addition, we provide an implementation of our system and give performance measurements.
---
paper_title: Conjunctive Broadcast and Attribute-Based Encryption

paper_content:

Attribute-based encryption (ABE) system enables an access control mechanism over encrypted data by specifying access policies among private keys and ciphertexts. There are two flavors of ABE, namely key-policy and ciphertext-policy, depending on which of private keys or ciphertexts that access policies are associated with. In this paper we propose a new cryptosystem called Broadcast ABE for both flavors. Broadcast ABE can be used to construct ABE systems with direct revocation mechanism. Direct revocation has a useful property that revocation can be done without affecting any non-revoked users; in particular, it does not require users to update keys periodically. For key-policy variant, our systems appear to be the first fully-functional directly revocable schemes. For ciphertext-policy variant, our systems improve the efficiency from the previously best revocable schemes; in particular, one of our schemes admits ciphertext and private key sizes roughly the same as the currently best (non-revocable) ciphertext-policy ABE. Broadcast ABE can also be utilized to construct multi-authority ABE in the disjunctive setting.
---
paper_title: Attribute-based encryption with non-monotonic access structures

paper_content:

We construct an Attribute-Based Encryption (ABE) scheme that allows a user's private key to be expressed in terms of any access formula over attributes. Previous ABE schemes were limited to expressing only monotonic access structures. We provide a proof of security for our scheme based on the Decisional Bilinear Diffie-Hellman (BDH) assumption. Furthermore, the performance of our new scheme compares favorably with existing, less-expressive schemes.
---
paper_title: Mediated Ciphertext-Policy Attribute-Based Encryption and Its Application

paper_content:

In Ciphertext-Policy Attribute-Based Encryption (CP-ABE), a user secret key is associated with a set of attributes, and the ciphertext is associated with an access policy over attributes. The user can decrypt the ciphertext if and only if the attribute set of his secret key satisfies the access policy specified in the ciphertext. Several CP-ABE schemes have been proposed, however, some practical problems, such as attribute revocation, still needs to be addressed. In this paper, we propose a mediated Ciphertext-Policy Attribute-Based Encryption (mCP-ABE) which extends CP-ABE with instantaneous attribute revocation. Furthermore, we demonstrate how to apply the proposed mCP-ABE scheme to securely manage Personal Health Records (PHRs).
---
paper_title: Adaptive-ID Secure Revocable Identity-Based Encryption

paper_content:

Identity-Based Encryption (IBE) offers an interesting alternative to PKI-enabled encryption as it eliminates the need for digital certificates. While revocation has been thoroughly studied in PKIs, few revocation mechanisms are known in the IBE setting. Until quite recently, the most convenient one was to augment identities with period numbers at encryption. All non-revoked receivers were thus forced to obtain a new decryption key at discrete time intervals, which places a significant burden on the authority. A more efficient method was suggested by Boldyreva, Goyal and Kumar at CCS'08. In their revocable IBE scheme, key updates have logarithmic (instead of linear in the original method) complexity for the trusted authority. Unfortunately, security could only be proved in the selective-ID setting where adversaries have to declare which identity will be their prey at the very beginning of the attack game. In this work, we describe an adaptive-ID secure revocable IBE scheme and thus solve a problem left open by Boldyreva et al. .
---
paper_title: Secure attribute-based systems

paper_content:

Attributes define, classify, or annotate the datum to which they are assigned. However, traditional attribute architectures and cryptosystems are ill-equipped to provide security in the face of diverse access requirements and environments. In this paper, we introduce a novel secure information management architecture based on emerging attribute-based encryption (ABE) primitives. A policy system that meets the needs of complex policies is defined and illustrated. Based on the needs of those policies, we propose cryptographic optimizations that vastly improve enforcement efficiency. We further explore the use of such policies in two example applications: a HIPAA compliant distributed file system and a social network. A performance analysis of our ABE system and example applications demonstrates the ability to reduce cryptographic costs by as much as 98% over previously proposed constructions. Through this, we demonstrate that our attribute system is an efficient solution for securely managing information in large, loosely-coupled, distributed systems.
---
paper_title: Attribute-Based Access Control with Efficient Revocation in Data Outsourcing Systems

paper_content:

Some of the most challenging issues in data outsourcing scenario are the enforcement of authorization policies and the support of policy updates. Ciphertext-policy attribute-based encryption is a promising cryptographic solution to these issues for enforcing access control policies defined by a data owner on outsourced data. However, the problem of applying the attribute-based encryption in an outsourced architecture introduces several challenges with regard to the attribute and user revocation. In this paper, we propose an access control mechanism using ciphertext-policy attribute-based encryption to enforce access control policies with efficient attribute and user revocation capability. The fine-grained access control can be achieved by dual encryption mechanism which takes advantage of the attribute-based encryption and selective group key distribution in each attribute group. We demonstrate how to apply the proposed mechanism to securely manage the outsourced data. The analysis results indicate that the proposed scheme is efficient and secure in the data outsourcing systems.
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paper_title: Attribute based data sharing with attribute revocation

paper_content:

Ciphertext-Policy Attribute Based Encryption (CP-ABE) is a promising cryptographic primitive for fine-grained access control of shared data. In CP-ABE, each user is associated with a set of attributes and data are encrypted with access structures on attributes. A user is able to decrypt a ciphertext if and only if his attributes satisfy the ciphertext access structure. Beside this basic property, practical applications usually have other requirements. In this paper we focus on an important issue of attribute revocation which is cumbersome for CP-ABE schemes. In particular, we resolve this challenging issue by considering more practical scenarios in which semi-trustable on-line proxy servers are available. As compared to existing schemes, our proposed solution enables the authority to revoke user attributes with minimal effort. We achieve this by uniquely integrating the technique of proxy re-encryption with CP-ABE, and enable the authority to delegate most of laborious tasks to proxy servers. Formal analysis shows that our proposed scheme is provably secure against chosen ciphertext attacks. In addition, we show that our technique can also be applicable to the Key-Policy Attribute Based Encryption (KP-ABE) counterpart.
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paper_title: New ciphertext-policy attribute-based access control with efficient revocation

paper_content:

Attribute-Based Encryption (ABE) is one of the promising cryptographic primitives for fine-grained access control of shared outsourced data in cloud computing. However, before ABE can be deployed in data outsourcing systems, it has to provide efficient enforcement of authorization policies and policy updates. However, in order to tackle this issue, efficient and secure attribute and user revocation should be supported in original ABE scheme, which is still a challenge in existing work. In this paper, we propose a new ciphertext-policy ABE (CP-ABE) construction with efficient attribute and user revocation. Besides, an efficient access control mechanism is given based on the CP-ABE construction with an outsourcing computation service provider.
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paper_title: Ciphertext-Policy Attribute-Based Encryption

paper_content:

In several distributed systems a user should only be able to access data if a user posses a certain set of credentials or attributes. Currently, the only method for enforcing such policies is to employ a trusted server to store the data and mediate access control. However, if any server storing the data is compromised, then the confidentiality of the data will be compromised. In this paper we present a system for realizing complex access control on encrypted data that we call ciphertext-policy attribute-based encryption. By using our techniques encrypted data can be kept confidential even if the storage server is untrusted; moreover, our methods are secure against collusion attacks. Previous attribute-based encryption systems used attributes to describe the encrypted data and built policies into user's keys; while in our system attributes are used to describe a user's credentials, and a party encrypting data determines a policy for who can decrypt. Thus, our methods are conceptually closer to traditional access control methods such as role-based access control (RBAC). In addition, we provide an implementation of our system and give performance measurements.
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paper_title: Mediated Ciphertext-Policy Attribute-Based Encryption and Its Application

paper_content:

In Ciphertext-Policy Attribute-Based Encryption (CP-ABE), a user secret key is associated with a set of attributes, and the ciphertext is associated with an access policy over attributes. The user can decrypt the ciphertext if and only if the attribute set of his secret key satisfies the access policy specified in the ciphertext. Several CP-ABE schemes have been proposed, however, some practical problems, such as attribute revocation, still needs to be addressed. In this paper, we propose a mediated Ciphertext-Policy Attribute-Based Encryption (mCP-ABE) which extends CP-ABE with instantaneous attribute revocation. Furthermore, we demonstrate how to apply the proposed mCP-ABE scheme to securely manage Personal Health Records (PHRs).
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paper_title: Conjunctive Broadcast and Attribute-Based Encryption

paper_content:

Attribute-based encryption (ABE) system enables an access control mechanism over encrypted data by specifying access policies among private keys and ciphertexts. There are two flavors of ABE, namely key-policy and ciphertext-policy, depending on which of private keys or ciphertexts that access policies are associated with. In this paper we propose a new cryptosystem called Broadcast ABE for both flavors. Broadcast ABE can be used to construct ABE systems with direct revocation mechanism. Direct revocation has a useful property that revocation can be done without affecting any non-revoked users; in particular, it does not require users to update keys periodically. For key-policy variant, our systems appear to be the first fully-functional directly revocable schemes. For ciphertext-policy variant, our systems improve the efficiency from the previously best revocable schemes; in particular, one of our schemes admits ciphertext and private key sizes roughly the same as the currently best (non-revocable) ciphertext-policy ABE. Broadcast ABE can also be utilized to construct multi-authority ABE in the disjunctive setting.
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paper_title: Attribute-based encryption with non-monotonic access structures

paper_content:

We construct an Attribute-Based Encryption (ABE) scheme that allows a user's private key to be expressed in terms of any access formula over attributes. Previous ABE schemes were limited to expressing only monotonic access structures. We provide a proof of security for our scheme based on the Decisional Bilinear Diffie-Hellman (BDH) assumption. Furthermore, the performance of our new scheme compares favorably with existing, less-expressive schemes.
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paper_title: Attribute-Based Encryption Supporting Direct/Indirect Revocation Modes

paper_content:

Attribute-based encryption (ABE) enables an access control mechanism over encrypted data by specifying access policies among private keys and ciphertexts. In this paper, we focus on ABE that supports revocation. Currently, there are two available revocable ABE schemes in the literature. Their revocation mechanisms, however, differ in the sense that they can be considered as direct and indirect methods. Direct revocation enforces revocation directly by the sender who specifies the revocation list while encrypting. Indirect revocation enforces revocation by the key authority who releases a key update material periodically in such a way that only non-revoked users can update their keys (hence, revoked users' keys are implicitly rendered useless). An advantage of the indirect method over the direct one is that it does not require senders to know the revocation list. In contrast, an advantage of the direct method over the other is that it does not involve key update phase for all non-revoked users interacting with the key authority. In this paper, we present the first Hybrid Revocable ABE scheme that allows senders to select on-the-fly when encrypting whether to use either direct or indirect revocation mode; therefore, it combines best advantages from both methods.
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paper_title: Multi-authority ciphertext-policy attribute-based encryption with accountability

paper_content:

Attribute-based encryption (ABE) is a promising tool for implementing fine-grained cryptographic access control. Very recently, motivated by reducing the trust assumption on the authority, and enhancing the privacy of users, a multiple-authority key-policy ABE system, together with a semi-generic anonymous key-issuing protocol, have been proposed by Chase and Chow in CCS 2009. Since ABE allows encryption for multiple users with attributes satisfying the same policy, it may not be always possible to associate a decryption key to a particular individual. A misbehaving user could abuse the anonymity by leaking the key to someone else, without worrying of being traced. In this paper, we propose a multi-authority ciphertext-policy (AND gates with wildcard) ABE scheme with accountability, which allows tracing the identity of a misbehaving user who leaked the decryption key to others, and thus reduces the trust assumptions not only on the authorities but also the users. The tracing process is efficient and its computational overhead is only proportional to the length of the identity.
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paper_title: Defending Against Key Abuse Attacks in KP-ABE Enabled Broadcast Systems

paper_content:

Key-Policy Attribute-Based Encryption (KP-ABE) is a promising cryptographic primitive which enables fine-grained access control over sensitive data. However, key abuse attacks in KP-ABE may impede its wide application especially in copyright-sensitive systems. To defend against this kind of attacks, this paper proposes a novel KP-ABE scheme which is able to disclose any illegal key distributor’s ID when key abuse is detected. In our scheme, each bit of user ID is defined as an attribute and the user secret key is associated with his unique ID. The tracing algorithm fulfills its task by tricking the pirate device into decrypting the ciphertext associated with the corresponding bits of his ID. Our proposed scheme has the salient property of black box tracing, i.e., it traces back to the illegal key distributor’s ID only by observing the pirate device’s outputs on certain inputs. In addition, it does not require the pirate device’s secret keys to be well-formed as compared to some previous work. Our proposed scheme is provably secure under the Decisional Bilinear Diffie-Hellman (DBDH) assumption and the Decisional Linear (DL) assumption.
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paper_title: Privacy-aware Attribute-based Encryption with User Accountability

paper_content:

As a new public key primitive, attribute-based encryption (ABE) is envisioned to be a promising tool for implementing fine-grained access control. To further address the concern of user access privacy, privacy-aware ABE schemes are being developed to achieve hidden access policy recently. For the purpose of secure access control, there is, however, still one critical functionality missing in the existing ABE schemes, which is user accountability. Currently, no ABE scheme can completely prevent the problem of illegal key sharing among users. In this paper, we tackle this problem by firstly proposing the notion of accountable, anonymous, and ciphertext-policy ABE (CP-A3BE, in short) and then giving out a concrete construction. We start by improving the state-of-the-art of anonymous CP-ABE to obtain shorter public parameters and ciphertext length. In the proposed CP-A3BE construction, user accountability can be achieved in black-box model by embedding additional user-specific information into the attribute private key issued to that user, while still maintaining hidden access policy. The proposed constructions are provably secure.
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paper_title: Accountable authority key policy attribute-based encryption

paper_content:

We present an accountable authority key policy attribute-based encryption (A-KPABE) scheme. In this paper, we extend Goyal’s work to key policy attribute-based encryption setting. We first generalize the notion of accountable authority in key policy attribute-based encryption scenario, and then give a construction. In addition, our scheme is shown to be secure in the standard model under the modified Bilinear Decisional Diffie-Hellman (mBDDH) assumption.
---
paper_title: Multi-authority ciphertext-policy attribute-based encryption with accountability

paper_content:

Attribute-based encryption (ABE) is a promising tool for implementing fine-grained cryptographic access control. Very recently, motivated by reducing the trust assumption on the authority, and enhancing the privacy of users, a multiple-authority key-policy ABE system, together with a semi-generic anonymous key-issuing protocol, have been proposed by Chase and Chow in CCS 2009. Since ABE allows encryption for multiple users with attributes satisfying the same policy, it may not be always possible to associate a decryption key to a particular individual. A misbehaving user could abuse the anonymity by leaking the key to someone else, without worrying of being traced. In this paper, we propose a multi-authority ciphertext-policy (AND gates with wildcard) ABE scheme with accountability, which allows tracing the identity of a misbehaving user who leaked the decryption key to others, and thus reduces the trust assumptions not only on the authorities but also the users. The tracing process is efficient and its computational overhead is only proportional to the length of the identity.
---
paper_title: Privacy-aware Attribute-based Encryption with User Accountability

paper_content:

As a new public key primitive, attribute-based encryption (ABE) is envisioned to be a promising tool for implementing fine-grained access control. To further address the concern of user access privacy, privacy-aware ABE schemes are being developed to achieve hidden access policy recently. For the purpose of secure access control, there is, however, still one critical functionality missing in the existing ABE schemes, which is user accountability. Currently, no ABE scheme can completely prevent the problem of illegal key sharing among users. In this paper, we tackle this problem by firstly proposing the notion of accountable, anonymous, and ciphertext-policy ABE (CP-A3BE, in short) and then giving out a concrete construction. We start by improving the state-of-the-art of anonymous CP-ABE to obtain shorter public parameters and ciphertext length. In the proposed CP-A3BE construction, user accountability can be achieved in black-box model by embedding additional user-specific information into the attribute private key issued to that user, while still maintaining hidden access policy. The proposed constructions are provably secure.
---
paper_title: Defending Against Key Abuse Attacks in KP-ABE Enabled Broadcast Systems

paper_content:

Key-Policy Attribute-Based Encryption (KP-ABE) is a promising cryptographic primitive which enables fine-grained access control over sensitive data. However, key abuse attacks in KP-ABE may impede its wide application especially in copyright-sensitive systems. To defend against this kind of attacks, this paper proposes a novel KP-ABE scheme which is able to disclose any illegal key distributor’s ID when key abuse is detected. In our scheme, each bit of user ID is defined as an attribute and the user secret key is associated with his unique ID. The tracing algorithm fulfills its task by tricking the pirate device into decrypting the ciphertext associated with the corresponding bits of his ID. Our proposed scheme has the salient property of black box tracing, i.e., it traces back to the illegal key distributor’s ID only by observing the pirate device’s outputs on certain inputs. In addition, it does not require the pirate device’s secret keys to be well-formed as compared to some previous work. Our proposed scheme is provably secure under the Decisional Bilinear Diffie-Hellman (DBDH) assumption and the Decisional Linear (DL) assumption.
---
paper_title: Accountable authority key policy attribute-based encryption

paper_content:

We present an accountable authority key policy attribute-based encryption (A-KPABE) scheme. In this paper, we extend Goyal’s work to key policy attribute-based encryption setting. We first generalize the notion of accountable authority in key policy attribute-based encryption scenario, and then give a construction. In addition, our scheme is shown to be secure in the standard model under the modified Bilinear Decisional Diffie-Hellman (mBDDH) assumption.
---
paper_title: Defending Against Key Abuse Attacks in KP-ABE Enabled Broadcast Systems

paper_content:

Key-Policy Attribute-Based Encryption (KP-ABE) is a promising cryptographic primitive which enables fine-grained access control over sensitive data. However, key abuse attacks in KP-ABE may impede its wide application especially in copyright-sensitive systems. To defend against this kind of attacks, this paper proposes a novel KP-ABE scheme which is able to disclose any illegal key distributor’s ID when key abuse is detected. In our scheme, each bit of user ID is defined as an attribute and the user secret key is associated with his unique ID. The tracing algorithm fulfills its task by tricking the pirate device into decrypting the ciphertext associated with the corresponding bits of his ID. Our proposed scheme has the salient property of black box tracing, i.e., it traces back to the illegal key distributor’s ID only by observing the pirate device’s outputs on certain inputs. In addition, it does not require the pirate device’s secret keys to be well-formed as compared to some previous work. Our proposed scheme is provably secure under the Decisional Bilinear Diffie-Hellman (DBDH) assumption and the Decisional Linear (DL) assumption.
---
paper_title: Privacy-aware Attribute-based Encryption with User Accountability

paper_content:

As a new public key primitive, attribute-based encryption (ABE) is envisioned to be a promising tool for implementing fine-grained access control. To further address the concern of user access privacy, privacy-aware ABE schemes are being developed to achieve hidden access policy recently. For the purpose of secure access control, there is, however, still one critical functionality missing in the existing ABE schemes, which is user accountability. Currently, no ABE scheme can completely prevent the problem of illegal key sharing among users. In this paper, we tackle this problem by firstly proposing the notion of accountable, anonymous, and ciphertext-policy ABE (CP-A3BE, in short) and then giving out a concrete construction. We start by improving the state-of-the-art of anonymous CP-ABE to obtain shorter public parameters and ciphertext length. In the proposed CP-A3BE construction, user accountability can be achieved in black-box model by embedding additional user-specific information into the attribute private key issued to that user, while still maintaining hidden access policy. The proposed constructions are provably secure.
---
paper_title: A ciphertext-policy attribute-based encryption scheme with constant ciphertext length

paper_content:

An Attribute-Based Encryption (ABE) is an encryption scheme where users with some attributes can decrypt ciphertexts associated with these attributes. The length of the ciphertext depends on the number of attributes in previous ABE schemes. In this paper, we propose a new Ciphertext-Policy Attribute-Based Encryption (CP-ABE) with constant ciphertext length. In our scheme, the number of pairing computations is also constant. In addition, the number of additional bits required from chosen plaintext attack-secure CP-ABE to chosen ciphertext attack-secure CP-ABE is reduced by 90% with respect to that of the previous scheme.
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paper_title: Divertible protocols and atomic proxy cryptography

paper_content:

First, we introduce the notion of divertibility as a protocol property as opposed to the existing notion as a language property (see Okamoto, Ohta [OO90]). We give a definition of protocol divertibility that applies to arbitrary 2-party protocols and is compatible with Okamoto and Ohta's definition in the case of interactive zero-knowledge proofs. Other important examples falling under the new definition are blind signature protocols. We propose a sufficiency criterion for divertibility that is satisfied by many existing protocols and which, surprisingly, generalizes to cover several protocols not normally associated with divertibility (e.g., Diffie-Hellman key exchange). Next, we introduce atomic proxy cryptography, in which an atomic proxy function, in conjunction with a public proxy key, converts ciphertexts (messages or signatures) for one key into ciphertexts for another. Proxy keys, once generated, may be made public and proxy functions applied in untrusted environments. We present atomic proxy functions for discrete-log-based encryption, identification, and signature schemes. It is not clear whether atomic proxy functions exist in general for all public-key cryptosystems. Finally, we discuss the relationship between divertibility and proxy cryptography.
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paper_title: Ciphertext-policy attribute-based encryption: an expressive, efficient, and provably secure realization

paper_content:

We present a new methodology for realizing Ciphertext-Policy Attribute Encryption (CP-ABE) under concrete and noninteractive cryptographic assumptions in the standard model. Our solutions allow any encryptor to specify access control in terms of any access formula over the attributes in the system. In our most efficient system, ciphertext size, encryption, and decryption time scales linearly with the complexity of the access formula. The only previous work to achieve these parameters was limited to a proof in the generic group model. ::: ::: We present three constructions within our framework. Our first system is proven selectively secure under a assumption that we call the decisional Parallel Bilinear Diffie-Hellman Exponent (PBDHE) assumption which can be viewed as a generalization of the BDHE assumption. Our next two constructions provide performance tradeoffs to achieve provable security respectively under the (weaker) decisional Bilinear-Diffie-Hellman Exponent and decisional Bilinear Diffie-Hellman assumptions.
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paper_title: A Ciphertext-Policy Attribute-Based Proxy Re-encryption with Chosen-Ciphertext Security

paper_content:

Cipher text-Policy Attribute-Based Proxy Re-Encryption (CP-ABPRE) extends the traditional Proxy Re-Encryption (PRE) by allowing a semi-trusted proxy to transform a cipher text under an access policy to the one with the same plaintext under another access policy (i.e. attribute-based re-encryption). The proxy, however, learns nothing about the underlying plaintext. CP-ABPRE has many real world applications, such as fine-grained access control in cloud storage systems and medical records sharing among different hospitals. Previous CP-ABPRE schemes leave how to be secure against Chosen-Cipher text Attacks (CCA) as an open problem. This paper, for the first time, proposes a new CP-ABPRE to tackle the problem. The new scheme supports attribute-based re-encryption with any monotonic access structures. Despite our scheme is constructed in the random oracle model, it can be proved CCA secure under the decisional q-parallel bilinear Diffie-Hellman exponent assumption.
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paper_title: Attribute based proxy re-encryption with delegating capabilities

paper_content:

Attribute based proxy re-encryption scheme (ABPRE) is a new cryptographic primitive which extends the traditional proxy re-encryption (public key or identity based cryptosystem) to the attribute based counterpart, and thus empower users with delegating capability in the access control environment. Users, identified by attributes, could freely designate a proxy who can re-encrypt a ciphertext related with a certain access policy to another one with a different access policy. The proposed scheme is proved selective-structure chosen plaintext secure and master key secure without random oracles. Besides, we develop another kind of key delegating capability in our scheme and also discuss some related issues including a stronger security model and applications.
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paper_title: Improved proxy re-encryption schemes with applications to secure distributed storage

paper_content:

In 1998, Blaze, Bleumer, and Strauss (BBS) proposed an application called atomic proxy re-encryption, in which a semitrusted proxy converts a ciphertext for Alice into a ciphertext for Bob without seeing the underlying plaintext. We predict that fast and secure re-encryption will become increasingly popular as a method for managing encrypted file systems. Although efficiently computable, the wide-spread adoption of BBS re-encryption has been hindered by considerable security risks. Following recent work of Dodis and Ivan, we present new re-encryption schemes that realize a stronger notion of security and demonstrate the usefulness of proxy re-encryption as a method of adding access control to a secure file system. Performance measurements of our experimental file system demonstrate that proxy re-encryption can work effectively in practice.
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paper_title: Attribute-based Proxy Re-encryption with a Constant Number of Pairing Operations

paper_content:

Attribute-based encryption (ABE) is an encryption scheme in which the user is able to decrypt a ciphertext with associated attributes. However, the scheme does not offer the capability of decryption to others when the user is offline. For this reason, the attribute-based proxy re-encryption (ABPRE) scheme was proposed, which combines traditional proxy re-encryption with ABE, so a user is able to empower designated users to decrypt the re-encrypted ciphertext with the associated attributes of designated users. However, previous ABPRE schemes demands a number of pairing operations that imply huge computational overhead. To reduce the number of pairing operations, we reduce the pairing operations with exponent operations. This paper provides a novel approach to an ABPRE scheme with constant pairing operation latency.
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paper_title: A ciphertext policy attribute-based encryption scheme without pairings

paper_content:

Sahai and Waters [34] proposed Attribute-Based Encryption (ABE) as a new paradigm of encryption algorithms that allow the sender to set a policy to describe who can read the secret data. In recent years, lots of attribute-based schemes appeared in literatures, but almost all the schemes, to the best of our knowledge, are constructed from pairings. In this work, we present a ciphertext policy attribute-based encryption (CP-ABE) scheme, which supports and-gates without pairings. Our scheme is defined on q-ary lattices, and has a very strong security proof based on worst-case hardness. More precisely, under the learning with errors (LWE) assumption, our CP-ABE scheme is secure against chosen plaintext attack in the selective access structure model. Though our scheme only encrypts one bit at a time, we point out that it can support multi-bit encryption by using a well-known technique. Besides, our result can be easily extended to ideal lattices for a better efficiency.
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paper_title: Fully Secure Functional Encryption: Attribute-Based Encryption and (Hierarchical) Inner Product Encryption

paper_content:

We present two fully secure functional encryption schemes: a fully secure attribute-based encryption (ABE) scheme and a fully secure (attribute-hiding) predicate encryption (PE) scheme for inner-product predicates. In both cases, previous constructions were only proven to be selectively secure. Both results use novel strategies to adapt the dual system encryption methodology introduced by Waters. We construct our ABE scheme in composite order bilinear groups, and prove its security from three static assumptions. Our ABE scheme supports arbitrary monotone access formulas. Our predicate encryption scheme is constructed via a new approach on bilinear pairings using the notion of dual pairing vector spaces proposed by Okamoto and Takashima.
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Title: A Survey of Research Progress and Development Tendency of Attribute-Based Encryption

Section 1: Introduction
Description 1: Introduce the background and the increasing demand for data sharing, as well as the requirements and limitations of traditional encryption mechanisms, leading to the evolution of Attribute-Based Encryption (ABE).

Section 2: Formal Model of the Basic ABE
Description 2: Discuss the formal definition, key generation, encryption, and decryption algorithms of the basic Attribute-Based Encryption scheme, along with the complexity assumptions and the security model.

Section 3: ABE Schemes
Description 3: Provide an overview of the Attribute-Based Encryption schemes, including KP-ABE, CP-ABE, Dual-policy ABE, and their comparative analysis in terms of complexity, security, and application scenarios.

Section 4: Multiauthority ABE
Description 4: Survey the development of multiauthority ABE schemes, distinguishing between schemes with a Central Authority (CA) and those without, along with their respective security challenges and solutions.

Section 5: Revocation Mechanism of ABE
Description 5: Examine various revocation mechanisms within ABE schemes, comparing indirect, direct, and hybrid approaches to user and attribute revocation.

Section 6: Accountable ABE
Description 6: Discuss the efforts and methods used to create accountable ABE schemes, addressing issues such as key abuse and illegal key sharing among users and authorities.

Section 7: Attribute-Based Proxy Reencryption
Description 7: Cover the integration of proxy reencryption with ABE, outlining the benefits, applications, and different construction methods of Attribute-Based Proxy Reencryption (ABPRE) schemes.

Section 8: Future Work
Description 8: Identify potential future research directions, addressing the need for optimization, efficiency improvements, alternative constructions, accountability, and practical applications of ABE schemes.

Section 9: Conclusion
Description 9: Summarize the current state of research in Attribute-Based Encryption, the progress made, and the aspects of ABE that remain active areas of investigation.