Cloud computing security : the scientific challenge , and a survey of solutions
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paper_title: Cloud computing privacy concerns on our doorstep

paper_content:

Privacy and confidentiality issues in cloud-based conference management systems reflect more universal themes.
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paper_title: Fully homomorphic encryption using ideal lattices

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We propose a fully homomorphic encryption scheme -- i.e., a scheme that allows one to evaluate circuits over encrypted data without being able to decrypt. Our solution comes in three steps. First, we provide a general result -- that, to construct an encryption scheme that permits evaluation of arbitrary circuits, it suffices to construct an encryption scheme that can evaluate (slightly augmented versions of) its own decryption circuit; we call a scheme that can evaluate its (augmented) decryption circuit bootstrappable. Next, we describe a public key encryption scheme using ideal lattices that is almost bootstrappable. Lattice-based cryptosystems typically have decryption algorithms with low circuit complexity, often dominated by an inner product computation that is in NC1. Also, ideal lattices provide both additive and multiplicative homomorphisms (modulo a public-key ideal in a polynomial ring that is represented as a lattice), as needed to evaluate general circuits. Unfortunately, our initial scheme is not quite bootstrappable -- i.e., the depth that the scheme can correctly evaluate can be logarithmic in the lattice dimension, just like the depth of the decryption circuit, but the latter is greater than the former. In the final step, we show how to modify the scheme to reduce the depth of the decryption circuit, and thereby obtain a bootstrappable encryption scheme, without reducing the depth that the scheme can evaluate. Abstractly, we accomplish this by enabling the encrypter to start the decryption process, leaving less work for the decrypter, much like the server leaves less work for the decrypter in a server-aided cryptosystem.
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paper_title: Fully homomorphic encryption with relatively small key and ciphertext sizes

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We present a fully homomorphic encryption scheme which has both relatively small key and ciphertext size. Our construction follows that of Gentry by producing a fully homomorphic scheme from a “somewhat” homomorphic scheme. For the somewhat homomorphic scheme the public and private keys consist of two large integers (one of which is shared by both the public and private key) and the ciphertext consists of one large integer. As such, our scheme has smaller message expansion and key size than Gentry’s original scheme. In addition, our proposal allows efficient fully homomorphic encryption over any field of characteristic two.
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paper_title: Flicker: an execution infrastructure for tcb minimization

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We present Flicker, an infrastructure for executing security-sensitive code in complete isolation while trusting as few as 250 lines of additional code. Flicker can also provide meaningful, fine-grained attestation of the code executed (as well as its inputs and outputs) to a remote party. Flicker guarantees these properties even if the BIOS, OS and DMA-enabled devices are all malicious. Flicker leverages new commodity processors from AMD and Intel and does not require a new OS or VMM. We demonstrate a full implementation of Flicker on an AMD platform and describe our development environment for simplifying the construction of Flicker-enabled code.
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paper_title: M.: Privacy Supporting Cloud Computing: ConfiChair, a Case Study

paper_content:

Cloud computing means entrusting data to information systems that are managed by external parties on remote servers, in the "cloud", raising new privacy and confidentiality concerns. We propose a general technique for designing cloud services that allows the cloud to see only encrypted data, while still allowing it to perform data-dependent computations. The technique is based on key translations and mixes in web browsers. ::: ::: We focus on the particular cloud computing application of conference management. We identify the specific security and privacy risks that existing systems like EasyChair and EDAS pose, and address them with a protocol underlying ConfiChair, a novel cloud-based conference management system that offers strong security and privacy guarantees. ::: ::: In ConfiChair, authors, reviewers, and the conference chair interact through their browsers with the cloud, to perform the usual tasks of uploading and downloading papers and reviews. In contrast with current systems, in ConfiChair the cloud provider does not have access to the content of papers and reviews and the scores given by reviewers, and moreover is unable to link authors with reviewers of their paper. ::: ::: We express the ConfiChair protocol and its properties in the language of ProVerif, and prove that it does provide the intended properties.
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paper_title: Privacy-supporting cloud computing by in-browser key translation

paper_content:

Cloud computing means entrusting data to information systems that are managed by external parties on remote servers, in the “cloud”, raising new privacy and confidentiality concerns. We propose a general technique for designing cloud services that allows the cloud to see only encrypted data, while still facilitating some data-dependent computations. The technique is based on key translations and mixes in web browsers.We focus on a particular kind of software-as-a-service, namely, services that support applications, evaluations and decisions. Such services include job application management, public tender management e.g., for civil construction, and conference management. We identify the specific security and privacy risks that existing systems pose. We propose a protocol that addresses them, and forms the basis of a system that offers strong security and privacy guarantees.We express the protocol and its properties in the language of ProVerif, and prove that it does provide the intended properties. We describe an implementation of a particular instance of the protocol called ConfiChair, which is geared to the evaluation of papers submitted to conferences.
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paper_title: Policy-sealed data: A new abstraction for building trusted cloud services

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Accidental or intentional mismanagement of cloud software by administrators poses a serious threat to the integrity and confidentiality of customer data hosted by cloud services. Trusted computing provides an important foundation for designing cloud services that are more resilient to these threats. However, current trusted computing technology is ill-suited to the cloud as it exposes too many internal details of the cloud infrastructure, hinders fault tolerance and load-balancing flexibility, and performs poorly. We present Excalibur, a system that addresses these limitations by enabling the design of trusted cloud services. Excalibur provides a new trusted computing abstraction, called policy-sealed data, that lets data be sealed (i.e., encrypted to a customer-defined policy) and then unsealed (i.e., decrypted) only by nodes whose configurations match the policy. To provide this abstraction, Excalibur uses attribute-based encryption, which reduces the overhead of key management and improves the performance of the distributed protocols employed. To demonstrate that Excalibur is practical, we incorporated it in the Eucalyptus open-source cloud platform. Policy-sealed data can provide greater confidence to Eucalyptus customers that their data is not being mismanaged.
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paper_title: TrustVisor: Efficient TCB Reduction and Attestation

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An important security challenge is to protect the execution of security-sensitive code on legacy systems from malware that may infect the OS, applications, or system devices. Prior work experienced a tradeoff between the level of security achieved and efficiency. In this work, we leverage the features of modern processors from AMD and Intel to overcome the tradeoff to simultaneously achieve a high level of security and high performance. We present TrustVisor, a special-purpose hypervisor that provides code integrity as well as data integrity and secrecy for selected portions of an application. TrustVisor achieves a high level of security, first because it can protect sensitive code at a very fine granularity, and second because it has a very small code base (only around 6K lines of code) that makes verification feasible. TrustVisor can also attest the existence of isolated execution to an external entity. We have implemented TrustVisor to protect security-sensitive code blocks while imposing less than 7% overhead on the legacy OS and its applications in the common case.
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paper_title: Ciphertext-Policy Attribute-Based Encryption

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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: Flicker: an execution infrastructure for tcb minimization

paper_content:

We present Flicker, an infrastructure for executing security-sensitive code in complete isolation while trusting as few as 250 lines of additional code. Flicker can also provide meaningful, fine-grained attestation of the code executed (as well as its inputs and outputs) to a remote party. Flicker guarantees these properties even if the BIOS, OS and DMA-enabled devices are all malicious. Flicker leverages new commodity processors from AMD and Intel and does not require a new OS or VMM. We demonstrate a full implementation of Flicker on an AMD platform and describe our development environment for simplifying the construction of Flicker-enabled code.
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paper_title: A protocol for property-based attestation

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The Trusted Computing Group (TCG) has issued several specifications to enhance the architecture of common computing platforms by means of new functionalities, amongst others the (binary) attestation to verify the integrity of a (remote) computing platform/application. However, as pointed out recently, the binary attestation has some shortcomings, in particular when used for applications: First, it reveals information about the configuration of a platform (hardware and software) or application. This can be misused to discriminate certain configurations (e.g., operating systems) and the corresponding vendors, or be exploited to mount attacks. Second, it requires the verifier to know all possible ``trusted'' configurations of all platforms as well as managing updates and patches that change the configuration. Third, it does not necessarily imply that the platform complies with desired (security) properties. A recent proposal to overcome these problems is to transform the binary attestation into property-based attestation, which requires to only attest whether a platform or an application fulfills the desired (security) requirements without revealing the specific software or/and hardware configuration.Based on previous works, we propose a concrete efficient property-based attestation protocol within an abstract model for the main functionalities provided by TCG-compliant platforms. We prove the security of this protocol under the strong RSA assumption and the discrete logarithm assumption in the random oracle model. Our scheme allows blind verification and revocation of mappings between properties and configurations.
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Title: Cloud Computing Security: The Scientific Challenge and a Survey of Solutions

Section 1: Introduction
Description 1: Provide an overview of cloud computing security challenges, emphasizing the unique scientific problem of securing data from cloud providers.

Section 2: Approaches to Achieving Confidentiality from the Cloud Provider
Description 2: Discuss the current methods including legislation, contracts, and internal processes, and the trust required between data owners and providers.

Section 3: Fully Homomorphic Encryption
Description 3: Explain the concept of fully homomorphic encryption and how it theoretically allows encrypted data processing in the cloud without revealing the data.

Section 4: Key Translation in the Browser
Description 4: Describe the method where data encrypted by users is translated by web browsers to facilitate secure data exchange without exposing plaintext data to the cloud.

Section 5: Hardware-Anchored Security
Description 5: Explore the use of specialized hardware to ensure that only approved programs can access decrypted data, thereby adding hardware-based security guarantees.

Section 6: CryptDB: A Weaker Attacker Model
Description 6: Cover CryptDB's approach to secure query processing over encrypted databases and its trade-offs between security and functionality.

Section 7: Discussion and Concrete Instances
Description 7: Integrate the discussion on the different approaches and provide specific examples and case studies, such as the conference management systems.

Section 8: Conclusions
Description 8: Summarize the key points, comparing the different approaches in terms of their applicability and security guarantees, and discuss potential future developments.