Mustafa Al-Bassam, Alberto Sonnino, Shehar Bano, Dave Hrycyszyn · 5 authors
Chainspace is a decentralized infrastructure, known as a distributed ledger, that supports user defined smart contracts and executes user-supplied transactions on their objects. The correct execution of smart contract transactions is verifiable by all. The system is scalable, by sharding state and the execution of transactions, and using S-BAC, a distributed commit protocol, to guarantee consistency. Chainspace is secure against subsets of nodes trying to compromise its integrity or availability properties through Byzantine Fault Tolerance (BFT), and extremely high-auditability, non-repudiation and `blockchain' techniques. Even when BFT fails, auditing mechanisms are in place to trace malicious participants. We present the design, rationale, and details of Chainspace; we argue through evaluating an implementation of the system about its scaling and other features; we illustrate a number of privacy-friendly smart contracts for smart metering, polling and banking and measure their performance.
Cloud computing has become an irreversible trend. Together comes the pressing need for verifiability, to assure the client the correctness of computation outsourced to the cloud. Existing verifiable computation techniques all have a high overhead, thus if being deployed in the clouds, would render cloud computing more expensive than the on-premises counterpart. To achieve verifiability at a reasonable cost, we leverage game theory and propose a smart contract based solution. In a nutshell, a client lets two clouds compute the same task, and uses smart contracts to stimulate tension, betrayal and distrust between the clouds, so that rational clouds will not collude and cheat. In the absence of collusion, verification of correctness can be done easily by crosschecking the results from the two clouds. We provide a formal analysis of the games induced by the contracts, and prove that the contracts will be effective under certain reasonable assumptions. By resorting to game theory and smart contracts, we are able to avoid heavy cryptographic protocols. The client only needs to pay two clouds to compute in the clear, and a small transaction fee to use the smart contracts. We also conducted a feasibility study that involves implementing the contracts in Solidity and running them on the official Ethereum network.
Νικόλαος Αλεξόπουλος, Jörg Daubert, Max Mühlhäuser, Sheikh Mahbub Habib
Trust Management (TM) systems for authentication are vital to the security of online interactions, which are ubiquitous in our everyday lives. Various systems, like the Web PKI (X.509) and PGP's Web of Trust are used to manage trust in this setting. In recent years, blockchain technology has been introduced as a panacea to our security problems, including that of authentication, without sufficient reasoning, as to its merits.In this work, we investigate the merits of using open distributed ledgers (ODLs), such as the one implemented by blockchain technology, for securing TM systems for authentication. We formally model such systems, and explore how blockchain can help mitigate attacks against them. After formal argumentation, we conclude that in the context of Trust Management for authentication, blockchain technology, and ODLs in general, can offer considerable advantages compared to previous approaches. Our analysis is, to the best of our knowledge, the first to formally model and argue about the security of TM systems for authentication, based on blockchain technology. To achieve this result, we first provide an abstract model for TM systems for authentication. Then, we show how this model can be conceptually encoded in a blockchain, by expressing it as a series of state transitions. As a next step, we examine five prevalent attacks on TM systems, and provide evidence that blockchain-based solutions can be beneficial to the security of such systems, by mitigating, or completely negating such attacks.
Daniel Augot, Hervé Chabanne, Olivier Clémot, William R. George
The most fundamental purpose of blockchain technology is to enable persistent, consistent, distributed storage of information. Increasingly common are authentication systems that leverage this property to allow users to carry their personal data on a device while a hash of this data is signed by a trusted authority and then put on a blockchain to be compared against. For instance, in 2015, MIT introduced a schema for the publication of their academic certificates based on this principle. In this work, we propose a way for users to obtain assured identities based on face-to-face proofing that can then be validated against a record on a blockchain. Moreover, in order to provide anonymity, instead of storing a hash, we make use of a scheme of Brands to store a commitment against which one can perform zero-knowledge proofs of identity. We also enforce the confidentiality of the underlying data by letting users control a secret of their own. We show how our schema can be implemented on Bitcoin's blockchain and how to save bandwidth by grouping commitments using Merkle trees to minimize the number of Bitcoin transactions that need to be sent. Finally, we describe a system in which users can gain access to services thanks to the identity records of our proposal.
The Intelligent vehicle (IV) is experiencing revolutionary growth in research and industry, but it still suffers from many security vulnerabilities. Traditional security methods are incapable to provide secure IV communication. The major issues in IV communication, are trust, data accuracy and reliability of communication data in the communication channel. Blockchain technology works for the crypto currency, Bit-coin, which is recently used to build trust and reliability in peer-to-peer networks having similar topologies as IV Communication. In this paper, we are proposing, Intelligent Vehicle-Trust Point (IV-TP) mechanism for IV communication among IVs using Blockchain technology. The IVs communicated data provides security and reliability using our proposed IV-TP. Our IV-TP mechanism provides trustworthiness for vehicles behavior, and vehicles legal and illegal action. Our proposal presents a reward based system, an exchange of some IV-TP among IVs, during successful communication. For the data management of the IV-TP, we are using blockchain technology in the intelligent transportation system (ITS), which stores all IV-TP details of every vehicle and is accessed ubiquitously by IVs. In this paper, we evaluate our proposal with the help of intersection use case scenario for intelligent vehicles communication.
Electronic voting presents many challenges due to its multiple security requirements. Some of the challenges are related to guaranteeing voters' privacy and system's transparency, which are hard to satisfy simultaneously. Electronic voting also presents other challenges such as usability, particularly from the voter's side. We study two particular problems of electronic voting. Cast-as-intended verifiability comprises those mechanisms which assure the voter that her cast ballot corresponds to her chosen voting options. Current proposals put the verification burden on the voter, something which is undesirable in real-world elections, where both technically skilled and non-skilled voters participate. In this thesis, we introduce the concept of universal cast-as-intended verifiability, which provides mechanisms which allow any entity to check that any ballot corresponds to the voter's selections - without revealing them. We formally define what universal cast-as-intended verifiability is and we give an electronic voting protocol satisfying this property. The other problem we have studied is the problem of invalid votes in electronic elections. Since a common selling point of electronic voting is that it avoids voters inadvertently spoiling their votes, deliberately spoiled ballots appearing in the tallying phase of an electronic election can cause mistrust on the system. Indeed, election stakeholders might think that the system is flawed or that it was exploited somehow. To avoid this situation, we define the concept of vote validatability, which states the electronic voting system should be able to detect spoiled ballots before they are successfully cast. In addition to formally defining this notion, we design an electronic voting protocol satisfying this property. All these security requirements of electronic voting systems are implemented with cryptographic tools. In addition to encryption and signature schemes, another essential primitive for building electronic voting protocols is zero-knowledge proofs. Zero-knowledge proofs allow a prover to convince a verifier that a statement is true without leaking any other information. These zero-knowledge proofs can be used to, for example, prove that the tally of the election was done properly. Recently, Groth and Sahai constructed efficient non-interactive zero-knowledge proofs for a wide range of statements including, among others, statements appearing in electronic voting. In this thesis we give two contributions on Groth-Sahai proofs. On the one hand, we give a framework for deriving cryptographic assumptions from which to build secure cryptographic protocols. In particular, we build new Groth-Sahai proofs improving the efficiency of currently known constructions. Independently, we show how the original Groth-Sahai proofs can be extended to be compatible with even more statements, how to improve their out-of-the-box efficiency for many of these statements and how to improve their re-usability efficiency among multiple statements. Els sistemes de vot electrònic presenten molts reptes a causa dels seus múltiples requeriments. Alguns d'aquests reptes estan relacionats amb garantir la privacitat del votant i la transparència del sistema, requisits que són difícils de satisfer al mateix temps. D'altra banda, els sistemes de vot electrònic presenten altres reptes com la usabilitat, sobretot de cara als votants. En aquesta tesi estudiem dos problemes del vot electrònic. La verificabilitat "cast-as-intended" tracta d'obtenir mecanismes que garanteixin al votant que el seu vot correspon a les seves preferències. Les propostes actuals posen la càrrega de la verificació en el votant, cosa que no és desitjable en eleccions del món real, on participen votants amb diferents graus de coneixements tècnics. Nosaltres introduïm el concepte de "universal cast-as-intended verifiability", que proporciona mecanismes per a que qualsevol entitat de l'elecció pugui comprovar que qualsevol vot conté les preferències del votant que l'ha emès - sense revelar el contingut del vot. A banda de definir formalment el concepte de "universal cast-as-intended verifiability" també proposem un protocol de vot electrònic que satisfà aquesta propietat. L'altre problema que hem estudiat és el problema dels vots invàlids en eleccions electròniques. Un dels avantatges del vot electrònic és que permet evitar que els votants emetin vots nuls sense voler. Per això, si durant el recompte de l'elecció apareixen vots nuls construïts intencionadament es pot crear desconfiança en el sistema de vot. Els usuaris del sistema de vot poden pensar que el sistema té forats de seguretat o que ha estat atacat. Per evitar aquesta situació, definim el concepte de "vote validatability", una propietat dels sistemes de vot electrònic que garanteix que els vots nuls es poden identificar en el moment que s'emeten. En aquesta tesi hem definit formalment aquesta propietat i hem dissenyat un protocol que la satisfà. Tots aquests requisits de seguretat dels protocols de vot electrònic s'implementen amb eines criptogràfiques. Les principals eines que s'utilitzen són esquemes de xifrat, esquemes de firma i proves de coneixement zero. Una prova de coneixement zero permet a una entitat convèncer una altra entitat que una sentència és certa sense donar cap altra informació que la certesa de la sentència. Aquestes proves de coneixement zero es poden fer servir, per exemple, per demostrar que el recompte de l'elecció s'ha fet correctament. Recentment, Groth i Sahai han construït proves de coneixement zero que es poden fer servir per un ampli ventall de sentències com per exemple sentències que apareixen en protocols de vot electrònic. En aquesta tesi hem fet dos contribucions sobre les proves de Groth i Sahai. Per una banda donem un marc teòric que permet derivar hipòtesis criptogràfiques per construir protocols criptogràfics. En particular, construïm noves proves de Groth i Sahai millorant l'eficiència de les construccions existents. De manera independent, indiquem com les proves de Groth i Sahai es poden estendre per fer-les compatibles amb un ventall més ampli de sentències, millorem l'eficiència de les proves de Groth i Sahai per moltes d'aquestes sentències i, en particular, quan es fan servir per demostrar múltiples sentències.
The Intelligent vehicle (IV) is experiencing revolutionary growth in research and industry, but it still suffers from many security vulnerabilities. Traditional security methods are incapable to provide secure IV data sharing. The major issues in IV data sharing are trust, data accuracy and reliability of data sharing data in the communication channel. Blockchain technology works for the crypto currency, Bit-coin, which is recently used to build trust and reliability in peer-to-peer networks having similar topologies as IV Data sharing. In this paper, we have proposed Intelligent Vehicle data sharing we are proposing a trust environment based Intelligent Vehicle framework. In proposed framework, we have use the blockchain technology as backbone of the IV data-sharing environment. The blockchain technology is provide the trust environment between the vehicles with the based on proof of driving.
A blockchain is a decentralized ledger where all transactions are recorded. For having a reliable blockchain and double-spending prevention, we need a decentralized consensus and agreement on a blockchain. Bitcoin uses proof-of-work (PoW). It is a cryptographic puzzle that is difficult to solve but easy to verify. However, because of significant latency of proof-of-work for transactions confirmation, this consensus mechanism is vulnerable against double-spending. On the other hand, PoW consumes a significant amount of energy that by growing the network, it becomes a major problematic of this consensus mechanism. In this paper, we introduce an alternative to PoW, because of all its major problems and security issues that may lead to collapsing decentralization of the blockchain, while a full decentralized system is the main purpose of using blockchain technology. The approach we introduce is based on a distributed voting process and called "RDV: Register, Deposit, Vote". Since in RDV algorithm, there is no mining process, so it is appropriate for low-level energy devices and Internet of Things (IoT).
A blockchain is a distributed ledger for recording transactions, maintained by many nodes without central authority through a distributed cryptographic protocol. All nodes validate the information to be appended to the blockchain, and a consensus protocol ensures that the nodes agree on a unique order in which entries are appended. Consensus protocols for tolerating Byzantine faults have received renewed attention because they also address blockchain systems. This work discusses the process of assessing and gaining confidence in the resilience of a consensus protocols exposed to faults and adversarial nodes. We advocate to follow the established practice in cryptography and computer security, relying on public reviews, detailed models, and formal proofs; the designers of several practical systems appear to be unaware of this. Moreover, we review the consensus protocols in some prominent permissioned blockchain platforms with respect to their fault models and resilience against attacks. The protocol comparison covers Hyperledger Fabric, Tendermint, Symbiont, R3~Corda, Iroha, Kadena, Chain, Quorum, MultiChain, Sawtooth Lake, Ripple, Stellar, and IOTA.
Abstract The I owe you (IOU) credit network Ripple is one of the most prominent alternatives in the burgeoning field of decentralized payment systems. Ripple’s path-based transactions set it apart from cryptocurrencies such as Bitcoin. Its pseudonymous nature, while still maintaining some regulatory capabilities, has motivated several financial institutions across the world to use Ripple for processing their daily transactions. Nevertheless, with its public ledger, a credit network such as Ripple is no different from a cryptocurrency in terms of weak privacy; recent demonstrative deanonymization attacks raise important concerns regarding the privacy of the Ripple users and their transactions. However, unlike for cryptocurrencies, there is no known privacy solution compatible with the existing credit networks such as Ripple. In this paper, we present PathShuffle, the first path mixing protocol for credit networks. PathShuffle is fully compatible with the current credit networks. As its essential building block, we propose PathJoin, a novel protocol to perform atomic transactions in credit networks. Using PathJoin and the P2P mixing protocol DiceMix, PathShuffle is a decentralized solution for anonymizing path-based transactions. We demonstrate the practicality of PathShuffle by performing path mixing in Ripple.
The systematic introduction to zero knowledge proof protocol has important theoretical guidance and practical significance on attracting more scholars involved in research as well as expanding application fields. Zero-knowledge proofs were first conceived in 1985 by Shafi Golwasser, Silvio Micalli and Charles Rackoff in a draft of the knowledge complexity of interactive proof systems. The goal of the present paper is to introduce a new identity based scheme which is a combination of zero-knowledge interactive proof and weil pairing on elliptic curves. The concept of weil pairing was first introduced by Andre Weil in 1940. It plays an important role in the theoretical study of the arithmetic of elliptic curves and Abelian varieties. It has also recently become extremely useful in cryptologic constructions related to these objects.
Bitcoin and other cryptocurrencies have surged in popularity over the last decade. Although Bitcoin does not claim to provide anonymity for its users, it enjoys a public perception of being a privacy preserving financial system. In reality, cryptocurrencies publish users' entire transaction histories in plaintext, albeit under a pseudonym; this is required for transaction validation. Therefore, if a user's pseudonym can be linked to their human identity, the privacy fallout can be significant. Recently, researchers have demonstrated deanonymization attacks that exploit weaknesses in the Bitcoin network's peer-to-peer (P2P) networking protocols. In particular, the P2P network currently forwards content in a structured way that allows observers to deanonymize users. In this work, we redesign the P2P network from first principles with the goal of providing strong, provable anonymity guarantees. We propose a simple networking policy called Dandelion which provides quasi-optimal, network-wide anonymity, with minimal cost to the network's utility. We also discuss practical implementation challenges and propose heuristic solutions.
Béla Gipp, Corinna Breitinger, Norman Meuschke, Joeran Beel
Manuscript submission systems are a central fixture in scholarly publishing. However, with existing systems, researchers must trust that their yet unpublished findings will not prematurely be disseminated due to technical weaknesses and that anonymous peer reviewers or committee members will not plagiarize unpublished content. To address this limitation, we present CryptSubmit - a system that automatically creates a decentralized, tamperproof, and publicly verifiable timestamp for each submitted manuscript by utilizing the blockchain of the cryptocurrency Bitcoin. The publicly accessible and tamperproof infrastructure of the blockchain allows researchers to independently verify the validity of the timestamp associated with their manuscript at the time of submission to a conference or journal. Our system supports researchers in protecting their intellectual property even in the face of vulnerable submission platforms or dishonest peer reviewers. Optionally, the system also generates trusted timestamps for the feedback shared by peer reviewers to increase the traceability of ideas. CryptSubmit integrates these features into the open source conference management system OJS. In the future, the method could be integrated at nearly no overhead cost into other manuscript submission systems, such as EasyChair, ConfTool, or Ambra. The introduced method can also improve electronic pre-print services and storage systems for research data.
Olivier Blazy, Philippe Gaborit, Julien Schrek, Nicolas Sendrier
In this paper we give the first blind signature protocol for code-based cryptography. Our approach is different from the classical original RSA based blind signature scheme, it is done in the spirit of the Fischlin approach [9] which is based on proofs of knowledge. To achieve our goal we consider a new tool for zero-knowledge (ZK) proofs, the Concatenated Stern ZK protocol, which permits to obtain an authentication protocol for concatenated matrices. A signature is then obtained from the usual Fiat-Shamir heuristic. We describe our blind signature protocol for cryptography based on Hamming metric and show how it can be extended to rank based cryptography. The security of our blind protocol is based on the security of a trapdoor function for the syndrome decoding problem: the CFS signature scheme for Hamming distance and on the more recent RankSign protocol for rank metric. We give proofs in the random oracle model (ROM) for our blind signature scheme, which rely on the Syndrome Decoding problem. The parameters we obtain for our protocol are practical for rank metric (200kBytes) for the signature length and 15kBytes for public key size) and a little less practical for Hamming distance.
This work show an avaliation about the performance of the application of Group Signature technique in Bitcoin system and a study about the anonymity and auditory. The Bitcoin’ goal is provide a virtual currency and an anonymous online transaction system. However, recent researches show that can be to break the anonymity of transactions through the chronological traceability technique in the Bitcoin transactions and analysis of network addresses. As a result of breaking anonymity of Bitcoin transactions, users’ privacy and all Bitcoin ecosystem are affected negatively. For this reason, in this work, it was proposed to include Group Signatures techniques in the Bitcoin system to increasing of anonymity in Bitcoin transactions but with audity possibility in accept time, more or less 10 minutes. The Group Signature generate a lot of dinstinct groups to dinstinct Bitcoin transactions. After to include the Group Signature technique in a modified version of Bitcoin system, we evaluated this technique in Bitcoin system through experiment in simulations. Through the experiments and statistic analysis, it was found that the approach of including the Group Signature is feasible for implementation in Bitcoin system with small groups, 500 clients. For the all cases analyzed, it was verified that the use of Group Signature in Bitcoin transactions increase the anonymity. Therefore, it was verified that the performance of Bitcoin transactions with Group Signature technique show a delay in nearly 50% less than current Bitcoin system whitout this technique. Nevertheless, in small groups with Group Signature get a better anonymity level and audity, but in big groups with more than 500 clients this technique not is good because the transactions time is over.
Disseminating medical data beyond the protected cloud of institutions poses severe risks to patients’ privacy, as breaches push them to the point where they abstain from full disclosure of their condition. This situation negatively impacts the patient, scientific research, and all stakeholders. To address this challenge, we propose a blockchain-based data sharing framework that sufficiently addresses the access control challenges associated with sensitive data stored in the cloud using immutability and built-in autonomy properties of the blockchain. Our system is based on a permissioned blockchain which allows access to only invited, and hence verified users. As a result of this design, further accountability is guaranteed as all users are already known and a log of their actions is kept by the blockchain. The system permits users to request data from the shared pool after their identities and cryptographic keys are verified. The evidence from the system evaluation shows that our scheme is lightweight, scalable, and efficient.
Alessandro Chiesa, Michael A. Forbes, Nicholas Spooner
Many seminal results in Interactive Proofs (IPs) use algebraic techniques based on low-degree polynomials, the study of which is pervasive in theoretical computer science. Unfortunately, known methods for endowing such proofs with zero knowledge guarantees do not retain this rich algebraic structure. In this work, we develop algebraic techniques for obtaining zero knowledge variants of proof protocols in a way that leverages and preserves their algebraic structure. Our constructions achieve unconditional (perfect) zero knowledge in the Interactive Probabilistically Checkable Proof (IPCP) model of Kalai and Raz [KR08] (the prover first sends a PCP oracle, then the prover and verifier engage in an Interactive Proof in which the verifier may query the PCP). Our main result is a zero knowledge variant of the sumcheck protocol [LFKN92] in the IPCP model. The sumcheck protocol is a key building block in many IPs, including the protocol for polynomial-space computation due to Shamir [Sha92], and the protocol for parallel computation due to Goldwasser, Kalai, and Rothblum [GKR15]. A core component of our result is an algebraic commitment scheme, whose hiding property is guaranteed by algebraic query complexity lower bounds [AW09,JKRS09]. This commitment scheme can then be used to considerably strengthen our previous work [BCFGRS16] that gives a sumcheck protocol with much weaker zero knowledge guarantees, itself using algebraic techniques based on algorithms for polynomial identity testing [RS05,BW04]. We demonstrate the applicability of our techniques by deriving zero knowledge variants of well-known protocols based on algebraic techniques, including the protocols of Shamir and of Goldwasser, Kalai, and Rothblum, as well as the protocol of Babai, Fortnow, and Lund [BFL91].
Double spending and blockchain forks are two main issues that the Bitcoin crypto-system is confronted with. The former refers to an adversary's ability to use the very same coin more than once while the latter reflects the occurrence of transient inconsistencies in the history of the blockchain distributed data structure. We present a new approach to tackle these issues: it consists in adding some local synchronization constraints on Bitcoin's validation operations, and in making these constraints independent from the native blockchain protocol. Synchronization constraints are handled by nodes which are randomly and dynamically chosen in the Bitcoin system. We show that with such an approach, content of the blockchain is consistent with all validated transactions and blocks which guarantees the absence of both double-spending attacks and blockchain forks.
Igor Zikratov, Alexander Kuzmin, Vladislav Akimenko, Viktor Niculichev · 5 authors
Blockchain is a relatively new technology that has shown a lot of possibilities. It emerged in 2009 as a public ledger of all Bitcoin transactions. Blockchain technology is finding applications in wide range of areas: digital assets and stocks, smart contracts, record keeping, ID systems, cloud storage, ride sharing, etc. We investigate the blockchains' activity in terms of how to store, retrieve and share files in decentralized network.
The blockchain has fueled one of the most enthusiastic bursts of activity in applied cryptography in years, but outstanding problems in security and privacy research must be solved for blockchain technologies to go beyond the hype and reach their full potential. At the first IEEE Privacy and Security on the Blockchain Workshop (IEEE S&B), we presented peer-reviewed papers bringing together academia and industry to analyze problems ranging from deploying newer cryptographic primitives on Bitcoin to enabling usecases like privacy-preserving file storage. We overview not only the larger problems the workshop has set out to tackle, but also outstanding unsolved issues that will require further cooperation between academia and the blockchain community.
This paper presents Prio, a privacy-preserving system for the collection of aggregate statistics. Each Prio client holds a private data value (e.g., its current location), and a small set of servers compute statistical functions over the values of all clients (e.g., the most popular location). As long as at least one server is honest, the Prio servers learn nearly nothing about the clients' private data, except what they can infer from the aggregate statistics that the system computes. To protect functionality in the face of faulty or malicious clients, Prio uses secret-shared non-interactive proofs (SNIPs), a new cryptographic technique that yields a hundred-fold performance improvement over conventional zero-knowledge approaches. Prio extends classic private aggregation techniques to enable the collection of a large class of useful statistics. For example, Prio can perform a least-squares regression on high-dimensional client-provided data without ever seeing the data in the clear.
Xavier Bultel, Jannik Dreier, Pascal Lafourcade, Malika More
At the main cryptography conference, CRYPTO, in 1989, Quisquater and colleagues published a paper showing how to explain the complex notion of zero-knowledge proof in a simpler way that children can understand. In the same line of work, this article presents simple and intuitive explanations of various modern security concepts and technologies, including symmetric encryption, public key encryption, homomorphic encryption, intruder models (CPA, CCA1, CCA2), and security properties (OW, IND, NM). The explanations given in this article may also serve in demystifying such complex security notions for non-expert adults.