10.6092/issn.2532-8816/9959
Negli ultimi anni la tecnologia blockchain si sta diffondendo sempre più su larga scala in diversi settori di ricerca, inclusi i Beni Culturali. Esistono diverse tipologie di blockchain, che possono essere classificate sia in base al tipo di utenti che possono accedervi, sia in base alle funzionalità che offrono. Questo articolo descrive uno studio teorico in cui si confrontano due blockchain molto diverse tra di loro: Ethereum e Hyperledger, al fine di definire quale delle due è maggiormente indicata per la memorizzazione di beni culturali tangibili contenuti in archivi digitali. Dopo una breve descrizione delle due tecnologie, verrà descritto un possibile scenario di applicazione abbastanza generico per poter capire quale delle due tecnologie meglio soddisfa i requisiti. Verrà quindi effettuato il confronto tra le due blockchain sulla base di problematiche generali, requisiti architetturali e considerazioni varie. Come risultato del confronto, emergerà che Hyperledger Fabric è più adatta nel contesto degli archivi digitali.
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The Use of Blockchain for Digital Archives: a comparison between Ethereum and Hyperledger (AIUCD 2019)
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2019-10-31
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Um. Dig.
Andrea Marchetti
2020/05/18
10.6092/issn.2532-8816/9959
Institute of Informatics and Telematics - National Research Council
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Accessed October 24, 2019
The Use of Blockchain for Digital Archives: a comparison between Ethereum and Hyperledger (AIUCD 2019)
https://umanisticadigitale.unibo.it/article/view/9959/10754
    Umanistica Digitale - ISSN:2532-8816 - n.8, 2020
A. Lo Duca, C. Bacciu, A. Marchetti – The Use of Blockchain for Digital Archives: a
comparison between Ethereum and Hyperledger
DOI: http://doi.org/10.6092/issn.2532-8816/9959


       The Use of Blockchain for Digital Archives: a
      comparison between Ethereum and Hyperledger

                     1
                      Angelica Lo Duca, 2Clara Bacciu, 3Andrea Marchetti

                                       IIT CNR, Pisa, Italy
                                1
                                  angelica.loduca@iit.cnr.it
                                   2
                                     clara.bacciu@iit.cnr.it
                               3
                                 andrea.marchetti@iit.cnr.it


       Abstract

In recent years, blockchain technology is progressively spreading on a large scale in various
research sectors, including Cultural Heritage. Different types of blockchain exist, which can be
classified either according to the type of users that can access them, or based on the features
they offer. This article describes a theoretical study in which two very different blockchains are
compared: Ethereum and Hyperledger, in order to define which of the two is more suitable for
storing tangible heritage contained in digital archives. After a brief description of the two
technologies, a possible generic application scenario will be described in order to understand
which of the two technologies best meets the requirements of the scenario. The comparison
between the two blockchains will therefore be carried out on the basis of general issues,
architectural requirements and various considerations. As a result of the comparison, it will
emerge that Hyperledger Fabric is more suitable in the context of digital archives.
Negli ultimi anni la tecnologia blockchain si sta diffondendo sempre più su larga scala in
diversi settori di ricerca, inclusi i Beni Culturali. Esistono diverse tipologie di blockchain, che
possono essere classificate sia in base al tipo di utenti che possono accedervi, sia in base alle
funzionalità che offrono. Questo articolo descrive uno studio teorico in cui si confrontano due
blockchain molto diverse tra di loro: Ethereum e Hyperledger, al fine di definire quale delle due
è maggiormente indicata per la memorizzazione di beni culturali tangibili contenuti in archivi
digitali. Dopo una breve descrizione delle due tecnologie, verrà descritto un possibile scenario
di applicazione abbastanza generico per poter capire quale delle due tecnologie meglio soddisfa
i requisiti. Verrà quindi effettuato il confronto tra le due blockchain sulla base di problematiche
generali, requisiti architetturali e considerazioni varie. Come risultato del confronto, emergerà
che Hyperledger Fabric è più adatta nel contesto degli archivi digitali.




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       Introduction

Recently, the diffusion of applications based on blockchain technology [21], [25] has been
increasing rapidly. The original focus of these technologies concerned cryptocurrencies (i.e.,
Bitcoin), but is shifting to finance and business in general, and is being extended progressively
for a variety of applications in healthcare, government, Internet of Things, entity and assets
management and eventually Cultural Heritage. In particular, a blockchain could be a good
solution to store, protect and preserve over time data about tangible heritage, especially minor
tangible heritage, i.e. artistically relevant artworks but not as famous as masterpieces. For
example, in case of disasters (either natural or man made), the fact that the blockchain is a
replicated registry can be exploited to retrieve information that in other circumstances would
otherwise be lost forever. In addition, information contained in the blockchain cannot be
erased or tampered with, so, in case of theft of the real artwork, related data will remain
available and would be used to recognise the work if someone tries to sell it and to detect
counterfeits. Using blockchain to store digital archives of artworks thus constitutes a promising
field of application.
This paper is an extension of the work illustrated in [2]. In particular, it describes the
challenges and requirements for storing a digital archive of artworks in a blockchain. In
addition, a possible framework based on blockchain is illustrated. Then the paper describes a
comparison between two blockchains, Ethereum1 [24] and Hyperledger Fabric2 [5], used as
main framework for digital archives. A preliminary implementation of a framework for digital
archives, based on Ethereum, has already been defined in [6], [3]. On the basis of the described
framework, a selection of some comparison criteria is done, including general issues related to
blockchains, architectural requirements applied to the specific architecture and other
considerations. As a result of the comparison, we can say Hyperledger Fabric better fits for the
proposed scenario because is more configurable. However, due to its popularity Ethereum still
remains a good solution.
In addition to Ethereum and Hyperledger there are other implementations of the blockchain
technology. Some of the most important are: Bitcoin [18], Corda,3 Quorum.4 Bitcoin was the
first blockchain. Based on open source code, it implements a decentralized digital
cryptocurrency where transactions are validated by miners through a rewarding process. Corda
is an open source blockchain platform, designed mainly for business applications. Similarly, to
Corda, Quorum, based on Ethereum with added control for permission and privacy, is a
blockchain envisaged mainly for business applications. A complete comparison among the
most important blockchains is done in [15]. The choice of which blockchain should be used to
store digital archives depends mainly on two aspects: firstly, the blockchain should be general,
i.e., not limited to financial applications. Secondly, it should be popular, i.e. technically mature

1   https://www.ethereum.org/
2   https://www.hyperledger.org/projects/fabric
3   https://www.corda.net/
4   https://www.jpmorgan.com/global/Quorum


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                                            comparison between Ethereum and Hyperledger

and with community guaranteeing long-term sustainability.
This paper compares only Ethereum and Hyperledger Fabric, mainly because they represent the
two main ways of implementing a blockchain: on the one hand Ethereum is the most
representative example of all permissionless blockchains. On the other hand, Hyperledger
represents permissioned blockchains. Both Ethereum and Hyperledger can be applied to specific
scenarios through the use of smart contracts/chain codes.
Bitcoin is a digital currency, and programmability is very limited. Corda, instead, is a more
recent blockchain, still not established as Ethereum and Hyperledger Fabric. Quorum is a
specific implementation of Ethereum, thus some considerations done for Ethereum are valid
also for Quorum.


       Related Works

The problem of managing records through a blockchain has been largely investigated during
the last few years. In her paper, Lemieux proposes a classification of blockchain applications
[16], based on which information is stored in the blockchain: a) mirror type, b) digital record
type, c) tokenized type.


       Mirror type
In the mirror type, the blockchain serves as a mirror, which stores only records fingerprints.
The complete information of a record is stored into an external repository and the blockchain
is used only to verify records integrity. In [9] the authors describe a first implementation of a
decentralized database for the storage of descriptive metadata related to digital records, based
on the combination of the blockchain and IPFS technologies. In their paper Liang et. al.
describe ProvChain [17], a system which guarantees data provenance in cloud environments.
Vishwa et. al. [23] illustrate a blockchain-based framework, which guarantees copyright
compliance of multimedia objects by means of smart contracts.


       Digital record type
In the digital record type, the blockchain is used to store all the records in the form of smart
contracts. In [4] the authors illustrate a distributed and tamper-proof framework for media.
Each media is represented by a watermark, which is firstly compressed and then stored into a
blockchain. Approved modifications to media are stored in the blockchain thus preventing
tampering. In [8] the authors describe Archain, a blockchain-based archive system, which stores
small sized records. Multiple roles are defined in the system, thus allowing records creation,
approval and removal.




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       Tokenized type
In the tokenized type, records are stored in the blockchain and they are linked to a
cryptocurrency. Adding, updating or removing a record has a cost. This constitutes an
innovative case, where the literature is not consolidated yet. An example of this type of
blockchain is represented by the Ubitquity Project, 5 which records land transactions on behalf
of companies and government agencies.


       Background


       The concept of Digital Archive
A digital archive is a repository of digital records that need long-term or even permanent
preservation for their cultural, historical, or evidentiary value. In digital archives, a record can
be anything holding a piece of information in the form of digital object, such as texts, images,
pictures, videos and audios. This paper focuses on digital archives which contain collections of
minor artworks. Minor artworks are artistically relevant works but not as well-known as famous
masterpieces, or belonging to the so-called minor arts, such as books and manuscripts, pottery,
lacquerware, furniture, jewellery, or textiles. Examples of minor tangible heritage could be
those kept in some small libraries or countryside churches, or even in private households.
The creation, management and sustainability of a digital archive is not an easy task, because
there is a series of issues that must be taken into consideration [1], [13], [26], [11]. The
InterPARES (International Research on Permanent Authentic Records in Electronic Systems)
series of projects [22] focused on creating policies and guidelines for making and maintaining
digital records, including authenticity requirements for record systems and long-term
preservation of digital records.
A digital archive is subject to obsolescence, in the sense that the hardware supports on which it
is stored change over time (from the floppy disk to the Internet cloud). Thus a digital archive
needs long-term preservation, i.e. digital artwork should remain accessible for a long period of
time depending on legal, regulatory, operational, and historical requirements. Secondly, every
artwork of the digital archive must be associated with different metadata (descriptive,
structural, administrative), which should be maintained up-to-date by authorized accounted
persons. This means that on the one hand that all the operations about the digital archive
should be documented in an open and verifiable manner (transparency). On the other hand,
artworks should be protected against forgery and identified correctly in case of loss and
subsequent discovery (anti-counterfeiting). Thirdly, records of the digital archive are stored in
different media formats, each defined by its own software and hardware. A digital archive
should guarantee the availability of all the formats, i.e. artworks should be efficiently and
accurately retrieved. Finally there are also other aspects that must be considered, such as
corruption and loss of information, which need protection, integrity and traceability of artworks.

5   http://ubitquity.io/brazil_ubitquity_llc_pilot.html


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                                             comparison between Ethereum and Hyperledger

Integrity makes sure that the digital description of the artwork is not subject to unauthorized
changes. Protection permits to protect the digital description of the artwork in case of natural
disasters and/or attacks (it is obviously impossible to protect the real work only with IT tools).
Traceability permits to trace all movements of individual artworks.
Another relevant issue concerns how difficult it can be to find and access repositories due to the
inconsistent description practices among different archives. The ISAD(G) (General
International Standard Archival Description) [7] is a standard that addresses this issue and gives
guidelines, to be used in conjunction with existing national standards, for the preparation of
archive descriptions that are effective in presenting the content of archival material, so that it is
easily identifiable and accessible. This description creates a hierarchy of metadata related to the
entire archive, as opposed to those related to each record.


       An overview of blockchain technology
A blockchain is a particular implementation of a Distributed Ledger (DL). A DL is essentially a
database, which is shared among different nodes of a network. In practice, all the nodes of the
network share the same copy of the database and any change made on a node, is replicated to
all the other nodes in few minutes and, in some cases, even in few seconds. A DL can be public
(as opposite of private) if any node can read the content, and permissionless (as opposed of
permissioned) if any node can write content (Table 1).
The protocol for the first functioning blockchain was introduced in 2008 to support the digital
cash Bitcoin, and implements the ledger as a chain of blocks. Each block contains data, a
timestamp and a cryptographic hash of the previous block. This way the integrity of the
information stored in the blockchain is protected through a security system based on
cryptography.
With respect to a standard database, a blockchain is an append-only register. This means that
information can only be added to the database, but it cannot be removed. Modifications to the
stored data can be done by re-uploading a new version of the data. A distributed consensus
algorithm is used to decide which updates to the ledger are to be considered valid. New
participants (nodes) can start collaborating to the maintenance of the repository by following
this algorithm. There is no need of a central authority or trust between nodes; the consensus
algorithm and cryptography grant the correctness of data even in the presence of some
malicious nodes.
Each block is made tamper-resistant by adding in its header a cryptographic signature of the
data it contains (usually a hash of the content), as well as a link to the previous block of the
chain (the cryptographic hash of the block). This way each block is dependent on the content
of all the previous blocks, making it impossible to modify the data contained in old blocks
without rewriting the new ones.
Initially designed for financial transactions, blockchain technology can be used to record
anything of value. Even executable code can be stored in the blockchain, the so-called smart


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contracts. A smart contract is not necessarily the transposition of a real contract, it is just code
that is executed by all the nodes of the blockchain network, and the result of the computation
is stored after a consensus is reached. A transaction carrying the payload of the contract is first
broadcast to the network. Its result is the deployment of the payload as code linked by its
public address. Any new transaction can then refer to this address to trigger the execution of
the functions inside the contract.
The big advantage of a blockchain is that it is an immutable, distributed, always available,
secure and publicly accessible repository of data. The main issues with blockchain
implementation of distributed ledgers are scalability and efficiency: often, consensus algorithms
that are used to grant consistency are expensive in terms of time and resources. In some cases, a
certain level of trust among participants can be present, thus simpler consensus algorithms can
be used.
Key technical choices of blockchain technology include:
1) permission design, i.e., whether permission is needed to access the blockchain;
2) choice of consensus algorithm, i.e., how a new block is added to the blockchain;
3) whether or not to use smart contracts, i.e., whether to use the blockchain as a virtual
machine where programs representing business processes are run;
4) whether or not to use a cryptocurrency, i.e., whether the consensus algorithm and smart
contract operations depend on an artificial currency or not.
Those technical choices often result from the governance model that has been chosen for the
ecosystem of participants.

                                    SOME                           ALL


 CAN READ                           PRIVATE                        PUBLIC


 CAN WRITE                          PERMISSIONED                   PERMISSIONLESS

Table 1: Types of blockchains according who can access what.


       Ethereum

Ethereum is a public open-source blockchain platform that has the capability of running so-
called decentralised applications (dApps). At the moment, the consensus algorithm is based on
Proof of Work. Mining nodes generate a cryptocurrency named Ether that is used to pay for
transactions. The key characteristic of Ethereum is that it is a programmable blockchain,
because it provides a Virtual Machine (EVM) that can execute user generated scripts (smart



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                                             comparison between Ethereum and Hyperledger

contracts) using the network of nodes. Smart contracts are usually written in Solidity 6 language
(but there are some alternatives), are compiled to EVM bytecode, and are deployed to the
blockchain for execution. Contract computation consumes gas, which is paid spending Ether.
Smart contracts are the foundation of dApps. Diagram in Figure 1 shows the simplified
architecture of dApps: there is no central server to which Web every browser has to connect,
but instead each one has its own instance of the application. Ethereum functions both as
storage for data and code, and as the machine that executes the code.




Figure 1: The architecture diagram of an Ethereum Dapp.


The Ethereum Network
The Ethereum network is a public distributed network with two types of nodes: full nodes and
lightweight nodes. Full nodes which contain the whole blockchain, i.e. all the validated
transactions. Some full nodes, called miners, are also responsible for transaction validation.
Miners can also be grouped in pools. Lightweight nodes contain a subset of the blockchain and
rely on full nodes for missing information. Examples of lightweight nodes are e-wallets, i.e.
electronic devices or apps which permit to do transactions.



6   https://solidity.readthedocs.io

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       Ether and Gas
As already said, Ethereum is cryptocurrency-based blockchain where the cryptocurrency used is
called Ether (ETH). The price of 1 ETH is 182.31 $ (updated on October 31, 2019). Together
with Ether there is also Gas, which is used to pay computational resources in the network ( gas
fee). The current value of Gas is called gas price. Every smart contract has associated a gas limit,
which is the maximum amount of gas which it can consume.


       Hyperledger

Hyperledger is an open source effort aimed at advancing cross-industry blockchain
technologies. Hyperledger focuses on developing different blockchain frameworks and modules
to support global enterprise solutions. Hyperledger blockchains are generally permissioned
blockchains, which means that the parties that want to join the network must be authenticated
and authorized. The focus of Hyperledger is to provide a transparent and collaborative
approach to blockchain development. Within Hyperledger, there are eight different technology
code projects, which define a common set of development principles: five distributed ledger
frameworks and three support modules. The Hyperledger frameworks include:
An append-only distributed ledger
A consensus algorithm for agreeing to changes in the ledger
Privacy of transactions through permissioned access
Smart contracts to process transaction requests.
In this paper only Hyperledger Fabric is described, because it is the most widespread. The
Hyperledger Fabric blockchain is a distributed system consisting of many nodes that
communicate with each other. Figure 2shows the Hyperledger Fabric Model.




Figure 2: The Hyperledger Fabric Model. Client A defines a chaincode (contract) through a transaction.
Once the transaction approved, client B can invoke methods contained in the chaincode through another
transaction.


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                                             comparison between Ethereum and Hyperledger


       Chaincodes and channels
The blockchain runs programs called chaincodes, holds state and ledger data, and executes
transactions. Chaincodes correspond to the Ethereum smart contracts. Each chaincode can be
invoked through one or more operations, called transactions. Transactions have to be endorsed
and only endorsed transactions may be committed and have an effect on the state of the ledger.
The most peculiar aspect of Hyperledger is the possibility to define channels, which are data
partitioning mechanisms that allow transaction visibility for only some defined users of the
blockchain. Each channel is an independent chain of transaction blocks containing only
transactions for that particular channel.
The ledger contains the current world state of the network and a chain of transaction
invocations. The world state reflects the current data about all the assets in the network. Ledger
provides a verifiable history of all successful state changes (valid transactions) and unsuccessful
attempts to change state (invalid transactions), occurring during the operation of the system.


       Roles and transactions
In Hyperledger two roles can be defined: clients and validators. Clients are applications that act
on behalf of a person to propose transactions on the network. Validators maintain the state of
the network and a copy of the ledger.
Unlike Ethereum, in Hyperledger Fabric there is no mining of blocks. In order to verify a
transaction, each transaction is sent to one trusted validator, which broadcasts it to all the other
validators of the network. All the validators reach consensus (using a specific algorithm) on the
order to follow to execute all the transactions. Then each validator runs the transactions on its
own, following the established order and builds a block with all the executed transactions.
Since the execution of transactions is deterministic, all the validators build exactly the same
block. Finally, the validators asynchronously notify the client application of the success or
failure of the transaction. Clients are notified by each validator.


       The model of blockchain for digital archives

The use of blockchain for digital archives guarantees a mechanism to access, manage and
protect cultural heritage on a daily basis and at times of disasters (due for example to climate
change or man-made). The blockchain-based framework should be designed both for minor
tangible heritage and major tangible and intangible heritage.
Thanks to the append-only-register property of the blockchain, the framework provides a
layered protection and conservation means for cultural heritage. The framework exploits also
some specific advantages of blockchain (integrity, transparency and authenticity of records) to
allow the secure storage of minor tangible heritage contained in digital archives. The framework
integrates also technologies for a distributed record storage, such as the InterPlanetary File


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System7 [14], in order to guarantee the digital preservation and transmission of tangible and
intangible heritage from generation to generation. The use of these storage technologies permits
the development of a sustainable protection and enhancement of values as well as the long-term
management of cultural heritage at risk.
Thanks to the benefits of blockchain and the distributed technologies for record storage, the
framework should improve sustainable access to digital heritage by contributing to the
resilience of our societies in terms of:
helping users to preserve the memory of cultural heritage in case of destruction of the physical
artwork, due to natural disasters or man-made disasters,
facilitating the restoration and/or the reconstruction of damaged heritage, thanks to the
information contained in the ledger,
preventing malicious changes to the ledger,
registering temporary movements of movable heritage, for example for exhibits.


       Requirements
The section The concept of Digital Archive describes the general requirements of a digital archive
(long-term preservation, transparency, anti-counterfeiting, protection, integrity and
traceability). The use of blockchain for digital archives should guarantee also the following
architectural requirements:
interoperability: this aspect should guarantee that the blockchain can easily interoperate with
external modules, such as web interfaces and external storage (i.e. IPFS);
customizable infrastructure: the system should guarantee that the underlying infrastructure is
customizable, e.g. the number of nodes and costs can be decided independently;
roles: the blockchain should define different users roles, according to what specified in the
previous section.
queries: this aspect refers to the ability to search data in the blockchain, e.g. search an artwork
by title or author.
In addition to these requirements, the following parameters that affect performance and
scalability should be taken into account [19]:
block frequency: inversely proportional to the time between two succeeding blocks. It is affected
by mining difficulty;
block size: the number of transactions that fit in a block;
network size: the number of nodes of the network. Increasing the number of nodes in the
network does not always improve performance. In fact, communication and consensus costs
may increase.

7   https://ipfs.io/


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                                             comparison between Ethereum and Hyperledger

throughput: the number of transactions per second;
latency: the time elapsed between the submission of a transaction and its validation;
finality: the property that once a transaction is completed, there is no way to alter it.


       Architecture
Errore: sorgente del riferimento non trovata describes the architecture of the blockchain-based
framework for digital archives. Starting from the bottom of the figure, there is a Data Lake
where all the descriptions of artworks are stored. The Data Lake is a distributed storage.
Artworks in Data Lake can be accessed through indexes contained in the blockchain. The
blockchain contains also other basic information related to artworks descriptions, as well as a
track of all the operations done on each artwork. This means that an external audit of the
framework can always verify the status of an artwork and determine if something is wrong. The
blockchain constitutes the backend of the framework, together with the Cache. The Cache
service stores basic information about artworks, such as author name and description, in order
to make users queries faster. In fact, natively, a blockchain is not suitable for fast queries such
those required by a web search engine.
The frontend of the framework is composed of the Authentication Service, which manages
users access to the system, and three interfaces, one for each type of user: Search, Publisher, and
Admin Interface. Users of the framework should play one of the following roles: generic user,
publisher, verifier. A generic user can search for an approved artwork in the system. A publisher
user can publish or update an artwork in the system. When a new artwork is published, its
status is set to pending. This means that the artwork is not approved yet thus cannot be
accessed by third parties neither can be updated by its author. A verifier is an expert in the field
to which the artwork belongs, and can vote for the approval of the artwork description. This
mechanism constitutes an algorithm for compliance with the principle of reliability of a record.
Complex strategies can be defined to establish how an artwork should be approved.




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Figure 3: The architecture of the blockchain-based framework.


Due to its intrinsic nature, the blockchain already satisfies the general requirements of a digital
archive, but long-term preservation, which is guaranteed through the Data Lake. Protection
would be achieved through the fact that the blockchain is replicated on different nodes. Anti-
counterfeiting would be guaranteed by associating each work to a sort of digital identity card,
containing all the information related to the work (including physical information). Finally,
integrity and traceability would be intrinsically guaranteed by the immutability and
timestamping properties of the blockchain. In fact, blockchain security assumptions guarantee
that if at a certain time a piece of information has been added to a block that reached
consensus, it will be impossible to alter that information without altering all the following
blocks.
Both Ethereum and Hyperledger Fabric satisfy the architectural requirements. However,
depending on the type of blockchain, there are the following additional issues that should be
taken into account:


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                                             comparison between Ethereum and Hyperledger

costs: whether or not every transaction has a fee;
popularity: how the blockchain is known, i.e. there is a supporting community and there are
skilled programmers able to implement contracts;
consensus: the distributed process which establishes the validation of transactions.


       Discussion

Table 2 illustrates issues associated with the proposed architecture for digital archives and how
the two blockchains address them. The fourth column of the table shows which blockchain fits
better the requirements for digital archives. Regarding costs, Hyperledger Fabric fits better to
the proposed architecture, because the network can be configured without costs on
transactions. This means that all the categories of users can access the blockchain freely.
However, if a business model were defined in the architecture, e.g. pay as you publish/access
resources, also Ethereum could be suitable for digital archives. Anyway, a private network can
be always set up on Ethereum, with a gas price set to zero, thus satisfying the model of the
proposed architecture.
When dealing with popularity, Ethereum is more popular and well-known than Hyperledger
Fabric. This means that a technical problem in the implementation of the described
architecture could find a greater support by the Ethereum community that the Hyperledger
one.
Regarding consensus, Ethereum bases it on Proof of Work, while Hyperledger Fabric
implements a permissioned voting-based consensus that implies a level of trust among
participants ad requires messages to be exchanged between nodes. In this case, Ethereum seems
to be more fit because of the lack of need for trust among participants.
Summarizing, from the point of view of issues, Ethereum seems to behave better than
Hyperledger Fabric, but for costs.




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 Issue                    Ethereum                   Hyperledger Fabric         Preferred blockchain

 Costs                    Every transaction has      Costs      can   be        Hyperledger Fabric
                          a cost dependent on        established    when
                          gas price (current is      configuring     the
                          about 4 gwei). In a        network
                          private blockchain,
                          the gas price can be
                          configured.

 Popularity               A    well-established A developing niche              Ethereum
                          and              wide community exists.
                          community       exist.
                          Many programmers
                          are able to write
                          smart contracts

 Consensus                Based on Proof of          Consensus algorithm        Ethereum
                          Work.                      requiring a level of
                                                     trust and message
                          The      larger the
                                                     overhead. The larger
                          network, the more
                                                     the network, more
                          reliable        the
                                                     time it takes to reach
                          consensus
                                                     consensus.

Table 2: Considerations about issues in the two blockchains and which one is more suitable for digital
archives.


Table 3 describes the architectural requirements and how the two blockchains satisfy them.
Like in the previous table, the fourth column specifies the preferred blockchain for a given
requirement. Firstly, referring to the customizable architecture, Hyperledger Fabric is to prefer,
because it permits to define who can access the network (permissioned blockchain). However,
Ethereum can be set up as a private blockchain, in the sense that there is a single organization
which manages it, and contracts handling user permissions can be implemented. Secondly,
looking at interoperability with external storage, Hyperledger Fabric is better than Ethereum,
because it has a native storage (data lake) and there is no need to configure external libraries to
access it. Anyway, if a programmer has good skills with Ethereum, the configuration of external
libraries to access external storage should not be difficult. The same analysis can be done for
interoperability with Web Interfaces. Thirdly, regarding roles, Hyperledger Fabric is more
configurable than Ethereum because of its native support of roles. Through channels,
Hyperledger Fabric can define also more complex access policies. When defining roles,
Ethereum has an overhead in terms of smart contracts thus is not indicated for the proposed


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                                                comparison between Ethereum and Hyperledger

architecture. Finally, queries are not supported neither by Ethereum nor by Hyperledger and
this aspect constitutes a limit of all blockchains. Thus, an additional mechanism based on
caching is defined in the architecture, in order to speed up data searches. Summarizing the
comparison about the architectural requirements, Hyperledger Fabric is the best solution.

    Requirement              Ethereum                   Hyperledger Fabric       Preferred blockchain

    Customizable             Ethereum is natively       Native support of        Hyperledger Fabric
    infrastructure           a public network,          permissioned
                             however a private          blockchain
                             blockchain can be
                             set up

    Interoperability with    External       libraries   No      support     to Hyperledger Fabric,
    external storage (e.g.   exist to support IPFS      external      storage but Ethereum is a
    IPFS)                    (e.g. Infura)8             because nodes in good alternative
                                                        hyperledger     fabric
                                                        have already a local
                                                        storage

    Interoperability with    External     libraries     Native support of        Hyperledger Fabric,
    Web Interfaces           exist (e.g. web3.js9       interoperability with    but Ethereum is a
                             and Drizzle)10             web interfaces (in       good alternative
                                                        Angular JS)11

    Roles                    A smart contract           Native support of        Hyperledger Fabric
                             must be defined to         roles through the
                             manage roles               definition of policies

    Queries                  No native support          No native support        -

Table 3: Considerations about architectural requirements in the two blockchains and which one is more
suitable for digital archives.


A direct comparison between Ethereum private and Hyperledger in terms of performance is

8      https://infura.io/
9      https://web3js.readthedocs.io/en/v1.2.2/
10 https://www.trufflesuite.com/docs/drizzle/quickstart
11 https://angularjs.org/

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difficult, due to the fact that are both highly configurable.
In general, how the protocol and the network are configured (starting from the choice of a
consensus algorithm) has a big impact on performance. An increase in mining difficulty leads
to a block frequency decrease, throughput decrease and latency rise. Block size and block
frequency are to be balanced (especially with PoW): incrementing block size improves
performance only if the block period is large enough for nodes to be able to create, sign,
propagate, execute transactions and reach consensus. Adding nodes to the network increases
computation capability, but if block frequency is high and block size is large, some nodes may
not have the resources to propagate information on time and keep in sync. Therefore, scaling is
limited by the design of the blockchain platform.
A study about performance and scalability of Ethereum private networks can be found in [19],
while performance metrics about Hyperledger are studied in [10].
As for the Ethereum public platform, average block frequency is 10-20 seconds, and average
block size is 20-30 KB. Troughput is about 15 transactions per second, with a latency of about
6 minutes. Current network size is 2.717.215 nodes.12
Summarizing, although Ethereum is more popular than Hyperledger Fabric, Hyperledger
Fabric seems more suitable to store digital archives, because it is highly configurable and
permits to define roles natively, without additional overhead. However, as the first
implementation of the proposed architecture, Ethereum is more indicated because of its
simplicity and popularity [6], [3].


       Conclusions and future work

This paper has presented challenges and requirements of storing digital archives through
blockchain. In addition, a possible architecture based on blockchain has been illustrated as well
as a preliminary comparison between Ethereum and Hyperledger Fabric as underlying
blockchains in a framework for storing, protecting and preserving digital archives. The paper
has compared the two blockchains at three levels: natively issues of the blockchain, architectural
requirements and general considerations. As a result, Hyperledger Fabric is more suitable to store
digital archives because of its high configurability.
We are aware that this study is preliminary, but we believe that the effort to define a possible
architecture of the framework, as well to select and analyse which parameters should be
considered when comparing two or more blockchains for digital archives storage is useful in
this field.
As already said in the introduction, an implemented use case of this architecture can be found
in [24], which exploits Ethereum as underlying blockchain. The further step should be the
implementation of the framework in Hyperledger Fabric and then a comparison of the two
implemented use cases.

12 https://etherscan.io/nodetracker/nodes


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                                        comparison between Ethereum and Hyperledger


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Last access URLs: 28th October 2019.




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