Blockchain-based Database to Ensure Data Integrity in Cloud

Blockchain-based Database to Ensure Data Integrity in Cloud
In Proceedings of the First Italian Conference on Cybersecurity (ITASEC17), Venice, Italy.
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Copyright Blockchain-based Database to Ensure Data Integrity
in Cloud Computing Environments
Edoardo Gaetani1 , Leonardo Aniello1 , Roberto Baldoni1 , Federico Lombardi1 ,
Andrea Margheri2 , and Vladimiro Sassone2
Research Center of Cyber Intelligence and Information Security, La Sapienza University of Rome
University of Southampton
Data is nowadays an invaluable resource, indeed it guides all business decisions in most of the
computer-aided human activities. Threats to data integrity are thus of paramount relevance, as tampering with data may maliciously affect crucial business decisions. This issue is especially true in cloud
computing environments, where data owners cannot control fundamental data aspects, like the physical
storage of data and the control of its accesses. Blockchain has recently emerged as a fascinating technology which, among others, provides compelling properties about data integrity. Using the blockchain
to face data integrity threats seems to be a natural choice, but its current limitations of low throughput,
high latency, and weak stability hinder the practical feasibility of any blockchain-based solutions.
In this paper, by focusing on a case study from the European SUNFISH project, which concerns the
design of a secure by-design cloud federation platform for the public sector, we precisely delineate the
actual data integrity needs of cloud computing environments and the research questions to be tackled
to adopt blockchain-based databases. First, we detail the open research questions and the difficulties
inherent in addressing them. Then, we outline a preliminary design of an effective blockchain-based
database for cloud computing environments.
Data is nowadays a key asset. It is strategic to drive any business decision in countless different
fields, ranging from finance and insurance, to health, education and public administration. As
computer-aided human activities are relying more and more on data, trusting data has thus
become crucial. At the same time, the critical role of data has made it a very appealing target
for cyber-attacks, which aim at undermining the fundamental CIA properties (Confidentiality,
Integrity, Availability) that data should exhibit in order to be trusted.
Cyber-attacks against CIA properties cause different impairments on data trust according
to the undermined property. Specifically, sabotaging availability prevents data to be retrieved
only for temporary period of time, but operations can be resumed as soon as data are accessible
again. Compromising confidentiality discloses instead private data and cannot be reverted, but
original data are still available and usable, at least to the extent allowed by the inflicted damage
(i.e., an organisation victim of data leakage may have to face economic consequences). Instead,
tampering with data integrity is a highly damaging attack that always paves critical issues to
data trust. Indeed, tampering with data can go undetected and drive operations maliciously, by
deleting specific entries (i.e., to remove inconvenient traces) or by altering particular sections of
data (i.e., to change data consumers’ behaviour). In 2015, Kaspersky Lab found out a massive
cyber-attack targeting over than 100 financial institutes worldwide that siphoned off money from
account balances for an estimated value of around $1 billion1 . Differently from confidentiality
and availability, once integrity is compromised there is no way to restore the original data, it
is lost forever. Therefore, as integrity attacks are subtle to be detected and really effective, in
this paper we focus on data integrity rather than confidentiality or availability.
Data integrity issues are exacerbated in cloud computing environments, as data owners
hardly control where their data are stored, who can actually access them, and in which way.
Nevertheless, more and more private and public organisations are outsourcing their data, because “it relieves the burden of maintenance cost as well as the overhead of storing data locally” [10]. Therefore, ensuring data integrity properties in cloud computing environments has
become an urgent need to address.
Data integrity is commonly assured by using, on one hand, cryptographic tools (i.e., digests,
asymmetric keys) and, on the other hand, appropriate data replication strategies. The cryptographic tools are indeed used to sign single pieces of data, so that any forging attack can be
promptly detected via cryptographic signature validations. Indeed, an attack to be effective
would require the violation of the secret keys, thus to update data signatures and circumvent
the cryptographic integrity checks. These attacks are challenging to carry out, but once realised
they are practically undetectable. Therefore, it is highly advocated to exploit appropriate data
replication strategies to ensure anyhow data integrity.
Replicating and distributing data over a set of nodes critically hamper the violation of
data integrity: an attacker should compromise, without being detected, all the replicated data.
This replication approach is widely adopted in practice, like, e.g., in the context of cloud
computing environments, where there is abundance of distributed storage resources. However,
although replication surely increases the burden for a successful attack in a cloud setting, cloud
providers themselves can collude with attackers for easily violating data integrity. To inhibit
these collusion attacks and to avoid blind trust on the integrity guarantees claimed by cloud
providers, we advocate an innovative exploitation of the blockchain technology to design and
implement a distributed, secure blockchain-based database for cloud computing environments.
Intuitively, a blockchain can be seen as a replicated database distributed among thousands
of nodes belonging to diverse parties. In its first conception it has been used as public ledger for
Bitcoin transactions [8]. Recently, it has gained a great momentum for the fascinating properties
it guarantees (e.g., distributed consensus, persistent and non-repudiable data) Among others,
the practical inability to alter an information that has been stored in a blockchain for “some
time” is the key focal point for data integrity. However, the actual length of such a time cannot
be fixed a priori and it becomes an insurmountable obstacle to effectively exploit blockchain.
For instance, a Bitcoin transaction is deemed tamper-proof about one hour after its insertion
in the blockchain; clearly an unfeasible period of time for, e.g., cloud computing applications.
Despite the time-related obstacle, the intrinsic replication and distribution features of
blockchains prompt their wide adoption in cloud settings. In this paper, we first shed light,
by introducing a few open research questions, on the issues of employing blockchain “as-is”.
Then, we present practical research directions that lead the way to effective blockchain-based
databases for cloud computing environments. On the one hand, we elaborate on the issues
of time-dependent integrity, lack of performance and absence of stability. On the other hand,
we propose an innovative blockchain-based database that permits balancing strong integrity
guarantees with appropriate performance and stability properties.
Structure of the paper. We first focus in Section 2 on a specific class of scenarios related to
SUNFISH, a European project about secure-by-design cloud federation, and to the data threats
its case studies prompt. In Section 3 we describe the blockchain technology, its data integrity
properties and current limitations, while we outline in Section 4 the research questions to address
to realise effective blockchain-based databases. In Section 5 we present our solution tackling
such questions and its application to the SUNFISH cloud federation case study. Finally, after
a brief discussion on related work in Section 6, we draw conclusions in Section 7.
Case Study: the European SUNFISH Project
Nowadays, an urgent need of public and private companies is to prompt and support interoperability and cooperation among their already deployed (private) cloud systems (see, e.g., the
ENISA report in [4]). Indeed, it is advocated that different cloud systems federate themselves
into goal-oriented federations. Besides the multiple technical issues to address, the creation
and management of cloud federations have to face daunting security issues, mainly related to
the non-disclosure of sensitive data and the enforcement of integrity guarantees. To overcome
these security difficulties, the EU SUNFISH project aims at proposing a distributed, democratic
cloud federation platform that will ensure by-design the security of the managed data.
The SUNFISH proposal is Federation-as-a-Service (FaaS) [9], a new and innovative service
that enables the secure creation and management of cloud data and services. FaaS features
advanced data security services and innovative design principles leading to a distributed and
democratic cloud federation governance. For the sake of presentation, we do not comment on
the data security services (further details are reported, e.g., in [12, 13]), while we extensively
address the role of data integrity in federation governance.
The intrinsic goal of cloud federations is sharing services among members by creating regulated, secured inter-cloud interactions. The rules governing these interactions, hence the service
usage, are defined in specific contracts. For instance, a member providing a service may require
that only specific consumers can use it and that the service outputs have to be masked for
privacy reasons. Due to the high sensitivity of the data managed by cloud federations (e.g.,
personal and medical data in case of the public sector), FaaS must provide high assurances
about the compliance of the member contracts. Indeed, besides the runtime enforcing of the
contracts, FaaS has to guarantee the integrity of contracts, namely that they cannot be tampered with and that all involved members must be aware of their existence. Additionally, to
ensure non-repudiable evidences of contract enforcement, all the inter-cloud interactions have
to be monitored and the logs stored with strong integrity guarantees.
Most of all, to foster a wide adoption of cloud federations, FaaS advocates the absence
of a centralised governance. As a matter of fact, among federation members there cannot
be designed a leader (i.e., there is no primus inter pares), rather federation members form a
network of peers. To this aim, FaaS seeks to establish a decentralised, democratic federation
governance, hence it must rely on an opportunely defined, distributed database ensuring strong
integrity guarantees. The novel design solution for FaaS advocated by the SUNFISH project is
based on the exploitation of a blockchain. To properly address the feasibility of such a solution,
significant threats to data integrity have to be identified.
Threats to Data Integrity
The threats to the data integrity in the context of cloud federation can be multiple and variegated. Our focus is on the database storing the governance data of a federation, hence on data
whose corruption critically affects the whole federation and its security. The threats we consider span from malicious alterations of data, to data updates without all the involved members
informed. More specifically, we can enumerate the following threats:
T1 An attacker violates the integrity of the data by directly altering (part of) the database.
T2 A federation member updates the database without informing the other members.
T3 Multiple federation members collude to maliciously altering (part of) the database.
Threat T1 is straightforward, while Threat T2 is due to the democratic nature of a SUNFISH federation. For instance, adding to the database a log entry about a fake inter-cloud
interaction between members A and B, hence without the A and B being informed, is a clear
integrity violation. Therefore, the process of adding data to the database should rely on opportunely devised consensus schemas. However, as pointed out in Threat T3, even consensus
schemas can be attacked: federation members can collude together to alter the database integrity. For instance, given a member A providing to the federation a service s, the other
members can collude to compromise s by, e.g., storing false information on the service (i.e., altering the contracts regulating the provisioning of s, or removing log entries about inappropriate
uses of s) to obtain advantages and causing the detriment of A.
Blockchain: Data Integrity, Performance, Stability
The blockchain is a quite novel technology that has appeared on the market in the recent
years, firstly used as public ledger for the Bitcoin cryptocurrency [8]. It mainly consists of
consecutive chained blocks containing records, that are replicated on the nodes of a p2p network.
These records witness transactions occurred between pseudonyms. Transactions may feature a
cryptocurrency like, e.g., the Bitcoin, or other kinds of assets. The collection of transactions
and their enclosing in chain blocks is carried out in a decentralised fashion by distinguished
nodes of the network, i.e. miners. Miners apply opportune block construction methods, i.e., the
mining process, to achieve consensus among all the miners on newly generated blocks. Bitcoin
is an example of permissionless blockchain, i.e., there is no restriction for a node to become
a miner. If instead there is an authentication and authorization layer for miners, then the
blockchain is permissioned.
The original mining process, still used for Bitcon and Ethereum [14] blockchain, is based on
the proof of work (PoW). It consists in a computational intensive hashing task that is regulated
according to the so-called blockchain difficulty that regulates the average time spent by miners
to accomplish such a task and create a new block. Once a miner achieves the creation of a new
block, it broadcasts that block to all the other miners. They consider such a block as the latest
of the chain and start mining new blocks to be appended. For the sake of simplicity, we can
say that once a miner has created a new block, it becomes part of the chain (if multiple miners
concurrently add a block, a transient fork is created which is usually quickly resolved because
by design miners always consider the longest chain).
PoW-based blockchains enjoy many fascinating properties related to data integrity, which
follow from the mining process and from the full replication of the blockchain on a large number
of nodes. Indeed, when a block is part of the chain, all miners have agreed on its contents,
hence it is practically non-repudiable and persistent (unless an attacker has the majority of
miners’ hash power that are able to create a fork of the chain). Assuming a majority of hash
power controlled by honest miners, the probability of a fork of depth n is O(2−n ) [2]. This gives
users high confidence that simply waiting for a small number of nodes to be added (6 blocks in
Bitcoin) will ensure their transactions are permanently included with high confidence.
However, PoW-based blockchains have a main drawback: performance. This lack of performance is mainly due to the broadcasting latency of blocks on the network and the time-intensive
task of PoW. As a matter of fact, each transaction stored on a blockchain has a high confirmation latency, which causes an extremely low transaction throughput. In Bitcoin, the average
latency is 10 minutes, and the throughput is about 7 transactions per second [2].
Another relevant concern related to the use of the blockchain regards its stability. Although,
e.g., the Bitcoin’s blockchain has worked quite well so far, there is no universally accepted
academic work explaining either why this has happened, or whether it will continue in the
future, or how long it will [2]. The stability properties of the PoW-based consensus protocol are
still being debated, and current “literature does not even provide adequate tools to assess under
which economic and social assumptions Bitcoin itself will remain stable” [2]. In general, PoWbased blockchains using incentive mechanisms based on cryptocurrencies are heavily subjected
to market fluctuations, which casts a shadow on the blockchain effectiveness on the long term.
Open Research Questions
In the context of cloud computing environments, the blockchain could be exploited to realise
a database ensuring strong integrity guarantees. In particular, the blockchain could be used
to store the logs of database operations, thus to avoid the data threats presented in Sec. 2.1.
However, current blockchains cannot be employed “as-is” due to various deficiencies. In the
following, we address the main issues related to data integrity, performance limitations, and
blockchain stability.
How to Measure Data Integrity? Once data has been included in a block, if we assume
a majority of honest miners, we can be highly confident that the chances of data alteration
decrease exponentially over time (see Sec. 3). Data integrity is indeed strictly related to these
chances. The more unlikely it is that data can be tampered with, the stronger the integrity
guarantees we can claim. However, being dependent on time introduces critical aspects to
address for ensuring data integrity: there is hardly information on the effective integrity guarantees once a transaction has just been sent to the blockchain. These observations suggest that
data integrity on blockchain cannot be simply seen as a binary property, which either holds or
does not, but it should be intended as a more complex, quantitative concept. This amounts to
take multiple factors into account, including the time and parties’ awareness. The described
issues thus lead us to formulate this research question:
Q1 How can we quantitatively characterise data integrity guarantees, in order to enable comparison among different blockchain-based database solutions?
Reasonable approaches to answer to this question should be based on the the effort an attacker
would spend to compromise data integrity without being detected.
How to Improve Performance? The performances currently achievable with PoW-based
blockchains are really poor as compared with classical database technologies. The experimented
latency and throughput are almost incompatible with the requirements of the considered cloud
scenarios. In this sense, a challenging and fundamental research problem regards the investigation of novel blockchain designs aimed at delivering performances aligned to today’s requirements, while keeping the needed integrity guarantees.
Q2 How can we design a blockchain-based database with better performances compared to a
PoW-based blockchain “as-is”, and with comparable data integrity guarantees?
The resulting designs should be flexible enough to enable variable tradeoff between performance
and integrity, thus to choose the setting that better fits the requirements.
How to Enhance Stability? Current PoW-based permissionless blockchains rely on a marketdependent cryptocurrency that may make the storing of data highly expensive and too dependent on market variations, i.e. it cannot ensure stability. Likewise poor performance cut out
many possible practical applications, unsatisfactory stability assurances can severely restrict
the applicability of blockchain to database. Enhancing the stability of PoW-based permissionless blockchains, e.g. Bitcoin’s, amounts to alter the currency incentives underlying the mining
process. Due to the large economic interests and speculation behind cryptocurrencies, such an
amendment is practically infeasible. A more viable path is exploiting permissioned blockchains,
where incentives do not depend on cryptocurrencies. The described path corresponds to answering the following research question:
Q3 How can we setup a permissioned blockchain having stronger stability compared to existing
PoW-based blockchains, while preserving required guarantees on data integrity?
The resulting blockchain will guarantee a stable support for the development of distributed
databased, as it is needed, e.g., in cloud computing environments.
Towards an Effective Blockchain-based Database
In this section we tackle the research questions just raised and we outline our proposal for
a more effective blockchain-based database. This proposal is thus intended to be part of the
SUNFISH project for ensuring high data integrity guarantees (hence, to deal with the data
threats presented in Sec. 2.1) and, at the same time, for being compliant with the performance
and stability requirements needed in a cloud computing environment.
Our blockchain-based database aims at providing a replicated database whose integrity is
testified via adequate evidences stored on a innovative designed blockchain system. Namely,
we devise a two-layer blockchain that, via the first-layer, ensures adequate performance and,
via a principled exploitation of the second-layer, ensures strong integrity guarantees. More
specifically, the first-layer employs a lightweight distributed consensus protocol that assures
low latency and high throughput. This layer aims at quickly and reliably storing evidences
of every operations carried out on a distributed database. However, this layer provides weak
data integrity guarantees due to the lack of PoW. Thus, the second-layer is designed as a
PoW-based blockchain that stores evidences of (a part of) the database operations logged by
the first-layer. These evidences are stored with strong data integrity guarantees but with poor
performance. Indeed, the principled interaction between the two layers permits obtaining an
overall performance improvement and effective assurances on data integrity.
In the following, we first present our proposal (Sec. 5.1), then we comment on the research
questions (Sec. 5.2) and finally show how the proposal deals with the identified threats (Sec. 5.3).
A Proposal for an Effective Blockchain-based Database
In this section we introduce our proposal for an effective blockchain-based database. Blockchain
is appropriately exploited to ensure the integrity of distributed replicas of a database, i.e. to
store persistent evidences of the database operations that cannot be repudiated. The use
of blockchain ensures not only integrity guarantees, but also fully distributed control of the
database data. This intrinsic characteristic makes our proposed database feasible to be used
in the context of FaaS federations. Figure 1 graphically depicts the proposed blockchain-based
database distributed on three clouds member of a federation.
The member clouds operating on the database issue operations through the Database Interface. The operations are first logged via appropriate evidences by the the first-layer blockchain,
then they are executed on the distributed DB replicas. More specifically, the first-layer
blockchain is permissioned, and features one miner on each member cloud. The miners, by
Figure 1: A blockchain-based database proposal for a Cloud Federation
relying on a public/private key pair to sign messages, achieve consensus by means of the socalled mining rotation consensus mechanism. Namely, it divides the time into rounds and, for
each round, elects a miner as a leader. The leader is then in charge of receiving new operations,
signing them with its private key, and broadcasting them to the other miners. Once all miners
have signed the operations, they can become part of the blockchain: all the miners add these
operations to their local ledger, and apply them to their local replica.
The interaction with the second-layer PoW-based blockchain is realised via a blockchain
anchoring technique. The anchoring technique is a timed operation that permits linking a
specific (part of) the first-layer blockchain with (a block of) the second-layer blockchain. In
particular, at certain intervals of time, a witness transaction containing the hash of the first-layer
blockchain up to the current operation is sent to the second-layer blockchain and, consequently,
stored as immutable, irreversible transaction. These hashes act as forensics evidence for proving
and validating the integrity of the data stored in the first-layer blockchain.
Preliminary Answers to the Research Questions
In the following, by referring to our proposal for blockchain-based databases, we introduce our
preliminary answers to the research questions previously reported.
Measuring Data Integrity. Our answer to Question Q1 is to measure the integrity as
the effort required for an attacker to change data in the blockchain without being noticed.
Quantifying this measure highly depends on the nature of the considered blockchain, but in
general a desiderata is that the longer data are stored in a blockchain, the greater the effort an
attacker should pay to break data integrity.
In our two-layer blockchain, the integrity measure on the evidences of a database operation
is crucially affected by which of the chain contains the evidences. Indeed, if the evidences are
only on the first-layer, the effort required for an attacker corresponds to compromise all the
replicas of the first-layer. However, as soon as the hash of the corresponding evidences has been
stored in the second-layer, an attacker should also subvert the integrity of the PoW, thus the
data integrity measure would be higher. As a matter of fact, on PoW-based blockchains like
Bitcoin’s, the attacker effort is close to infinite [6], i.e. it is an infeasible attack.
Improving Performance. The lack of performance of current blockchain-based systems, i.e.
Question Q2, is due to PoW. To provide better performance to blockchain users, our proposal
offers to clients a blockchain based on lightweight consensus algorithm and leverages on the
power of PoW only in the background, i.e. the second-layer. Therefore, from the point of view
of a client of the blockchain-based database, an operation on the database is completed as soon
as it is elaborated by the first-layer blockchain.
Enhancing Stability. Permissionless blockchains like Bitcoin’s and Ethereum’s are natural
candidates for the second-layer blockchain. To enhance their stability, i.e. Question Q3, we
advocate the use of a blockchain that does not feature a market-dependent cryptocurrency
and mining incentive mechanisms. Broadly speaking, the stability needs for blockchain highly
depend on the application context. For example, in the case of the SUNFISH case studies,
which address the European public sector, the need of stability is of paramount importance.
In this context, we could hence envision a European permissioned PoW-based blockchain that
will offer a common, stable underlying support for all European administrations.
Addressing Threats to Data Integrity
With reference to the threats outlined in Sec. 2.1, in this section we explain how the solution
we propose successfully addresses them.
The effort required for an attacker to tamper with stored data (Threat T1) has been previously discussed in this section. At the very least, all the miners of the first-layer blockchain
should be compromised, e.g. stealing their private keys. In the setting of FaaS, this would
requires attacking multiple distributed cloud providers simultaneously. Even if this unlikely
situation occurs, the anchoring with the second-layer blockchain ensures that only the latest
set of operations on the database can be subverted; all the others are testified by immutable,
irreversible evidences.
The consensus algorithm featured by the first-layer blockchain takes by design into account
all the miners, hence the member clouds. Therefore, there cannot be any database operation
completed without all the members being aware of it (Threat T2).
Collusion attacks (Threat T3) are instead equivalent to compromising first-layer blockchain
miners. All the private keys of these miners are required to sign the messages needed to complete
a database operation, thus even in the case of a single honest member attacked by a coalition
formed by all the others, such honest member could successfully react. Namely, it could prevent
a malicious database operation to complete by not sending its message within the consensus
protocol. If the coalition attack was instead aimed to alter an information already stored in the
first-layer blockchain, this means that such information has been previously agreed on by all
the members, thus an honest member could then prove it owns the intact version by showing
the messages previously signed and sent by the other members (when the consensus on that
information was firstly achieved).
Related Work
Data Integrity is a well known problem in computing systems, especially for cloud environments,
where users outsource their data. The task of checking data integrity for a user having relatively
poor computing devices might be very heavy due to huge amount of data to download. Ateniese
et al. [1] provide one of the first model that enables a client to verify the integrity of her
outsourced data on a single server without retrieving them. For a cloud environments, Remote
Data Auditing (RDA) is a solution to enable auditability of outsourced data through a trusted
third-party, which alleviates the computation burden on the user. A number of RDA techniques
have been proposed to improve both security and efficiency, as Sookhak et al. reviewed and
classified in their survey [11]. All these works rely on the assumption that the third-party is
trusted. If the latter acts instead maliciously, they can no longer ensure integrity. By taking
advantage of the PoW-based blockchain immutability feature,our solution is able to ensure data
integrity also in a trust-less environment.
The first-layer blockchain we use to improve performance is inspired by Bitcoin-NG [5], a
Bitcoin protocol modified to improve performances. To this aim they sacrifice some security
guarantees, indeed data integrity is ensured only under the assumption of a majority of honest
miners. Other blockchain-based databases have been proposed in literature. A similar work to
ours is BigchainDB [7], a NoSQL-like storage on top of a blockchain with a built-in consensus
approach. Similarly to BitCoin-NG, their main goal is to improve performances sacrificing
some security guarantees. Indeed, in case of a majority of malicious miners, they can no longer
ensure data integrity, similarly to Bitcoin-NG. Our solution, contrarily from both Bitcoin-NG
and BigchainDB, can ensure data integrity even in case of a majority of malicious miners.
Indeed, we have shown in Sec. 5.3 that we can guarantee integrity when all the miners but one
are malicious and collude among themselves, therefore we can still assure integrity when overall
the attacker is weaker, i.e., when a majority of miners (thus a lower number, assuming at least
three miners) are malicious (thus, maybe they don’t collude among themselves at all).
A remarkable work aimed at improving performance while providing security guarantees
is RSCoin [3], i.e. a cryptocurrency framework that introduces a centralisation degree. A
central bank maintains complete control over the monetary supply, but relies on mintettes, i.e.
a distributed set of authorities used to prevent double-spending. They show how their solution,
based on a proper consensus algorithm, allows to improve performances and ensure integrity.
However, compared to our solution, their work has two main limitations: (i) a centralisation
degree and (ii) integrity guarantees reached only with a majority of honest mintettes.
In this paper we identified the requirements and research questions to be addressed to realise a
blockchain-based database for cloud computing environments, grounding on real needs arisen in
the European project SUNFISH. Our main contribution is the proposal of a high-level solution
which answers these questions, and lies the foundations for the design of a blockchain-based
database able to provide the desired guarantees on data integrity, performance, and stability.
This work paves the way to appealing future works. The direction we propose can be
further investigated by realising a working prototype to validate the effectiveness of our solution,
in terms of achievable latency and throughput. Furthermore, a more thorough and formal
examination of the tradeoff between performance and data integrity guarantees is required to
prove the efficacy of our design against the identified threats. It is worth finally noticing that
our blockchain-based database proposal, in this preliminary design, has been designed upon
a total consensus mechanism. The approach surely permits to achieve integrity among the
distributed replicas and to simplify the thread addressing. However, its availability can be
critically affected by violating only a single miner. On the path of deploying such a database,
we are designing an appropriate fault-tolerant consensus algorithm that permits combination
of integrity with also availability. Finally, researching on the feasibility of realising more stable
blockchains is fundamental to enable their wide adoption as reliable storage infrastructures, e.g.
in the context of cloud computing environments.
This work has been supported by the European Commissions H2020 Programme under the
SUNFISH project, grant N.644666.
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