Blockchain Papers

Robert Herian

No abstract is available for this record.

Zheng Yang, Hang Lei

This article presents the formal syntax and semantics for a large subset of the Solidity programming language developed for the Etheruem blockchain platform based on our resent work about developing a general, extensible, and reusable formal memory (GERM) framework and an extension of Curry-Howard isomorphism, denoted as execution-verification isomorphism (EVI). This subset is denoted as Lolisa, which, to our knowledge, is the first mechanized and validated formal syntax and semantics developed for Solidity. The formal syntax of Lolisa adopts a stronger static type system than Solidity for enhanced type safety. In addition, Lolisa not only includes nearly all the syntax components of Solidity, such as mapping, modifier, contract, and address types, but it also contains general-purpose programming language features, such as multiple return values, pointer arithmetic, struct, and field access. Therefore, the inherent compatibility of Lolisa allows Solidity programs to be directly translated into Lolisa with a line-by-line correspondence without rebuilding or abstracting, and, in addition, the inherent generality of Lolisa allows it to be extended to express other programming languages as well. To this end, we also present a preliminary scheme for extending Lolisa to other languages systematically.

Susumu Kiyoshima

No abstract is available for this record.

Hilarie Orman

I would like to jump on the blockchain bandwagon. I would like to be able to say that blockchain is the solution to the longstanding problem of secure identity on the Internet. I would like to say that everyone in the world will soon have a digital identity. Put yourself on the blockchain and never again ask yourself, Who am I? - you are your blockchain address.

Mega Satish, Indranil Sengupta, K. Pratap

This paper presents the implementation of an interactive Zero Knowledge Password authentication scheme for commercial Web sites. In this scheme, a legitimate prover (client) can exchange a secret code (password) with a remote skeptic (server), in order to reveal his/her identification. Based on the validity of the secret code the skeptic then allows the prover to login to the site and access the web services. This paper introduces a protocol that integrates the concepts of Discrete Logarithm Problem (DLP) and Zero-Knowledge Proofs (ZKP). The protocol consists of three entities, namely, the prover, the skeptic, and the facilitator who interact with one another to generate the secret code. When tested, the time to carry out various operations related to this protocol was reasonably small (under 4 seconds). Our scheme is resistant to man-in-the-middle attack and discourages replaying previously intercepted secret codes. We also propose two modifications to our basic scheme to make it resistant against the attack on Integrity and Denial of Service attack (DOS).

Ayad Al-Adhami

Radio Frequency Identification (RFID) technology has been expanded to be used in different fields that need automatic identifying and verifying of tagged objects without human intervention. RFID technology offers a great advantage in comparison with barcodes by providing accurate information, ease of use and reducing of labour cost. These advantages have been utilised by using passive RFID tags. Although RFID technology can enhance the efficiency of different RFID applications systems, researchers have reported issues regarding the use of RFID technology. These issues are making the technology vulnerable to many threats in terms of security and privacy. Different RFID solutions, based on different cryptography primitives, have been developed. Most of these protocols focus on the use of passive RFID tags. However, due to the computation feasibility in passive RFID tags, these tags might be vulnerable to some of the security and privacy threats. , e.g. unauthorised reader can read the information inside tags, illegitimate tags or cloned tags can be accessed by a reader. Moreover, most consideration of reserchers is focus on single tag authentication and mostly do not consider scenarios that need multi-tag such as supply chain management and healthcare management. Secret sharing schemes have been also proposed to overcome the key management problem in supply chain management. However, secret sharing schemes have some scalability limitations when applied with high numbers of RFID tags. This work is mainly focused on solving the problem of the security and privacy in multi-tag RFID based system. In this work firstly, we studied different RFID protocols such as symmetric key authentication protocols, authentication protocols based on elliptic curve cryptography, secret sharing schemes and multi-tag authentication protocols. Secondly, we consider the significant research into the mutual authentication of passive RFID tags. Therefore, a mutual authentication scheme that is based on zero-knowledge proof have been proposed . The main object of this work is to develop an ECC- RFID based system that enables multi-RFID tags to be authenticated with one reader by using different versions of ECC public key encryption schemes. The protocol are relied on using threshold cryptosystems that operate ECC to generate secret keys then distribute and stored secret keys among multi RFID tags. Finally, we provide performance measurement for the implementation of the proposed protocols.

Mengjie Chen, Yuexuan Li, Zhuocheng Xu, Xin Huang · 5 authors

No abstract is available for this record.

Charanjit S. Jutla, Arnab Roy

No abstract is available for this record.

Seongseop Kim, David J. Wu

Non-interactive zero-knowledge (NIZK) proofs are fundamental to modern cryptography. Numerous NIZK constructions are known in both the random oracle and the common reference string (CRS) models. In the CRS model, there exist constructions from several classes of cryptographic assumptions such as trapdoor permutations, pairings, and indistinguishability obfuscation. However, at the time of the initial publication of this work, we did not have constructions of NIZKs from standard lattice assumptions. In this work, we take an initial step toward constructing multi-theorem NIZKs for general $$\mathsf {NP}$$ languages from standard lattice assumptions by considering a relaxation to the preprocessing model and a new model we call the designated-prover model. In the preprocessing model, a setup algorithm generates secret proving and verification keys for the prover and the verifier, respectively. In the designated-prover model, the proving key is secret, but the verification key is public. In both settings, the proving key is used to construct proofs and the verification key is used to check proofs. Finally, in the multi-theorem setting, both the proving and verification keys should be reusable for an unbounded number of theorems without compromising soundness or zero-knowledge. Previous constructions of NIZKs in the preprocessing model that rely on weaker assumptions like one-way functions or oblivious transfer are only secure in a single-theorem setting. Thus, constructing multi-theorem NIZKs in these relaxed models does not seem to be inherently easier than constructing them in the CRS model. In this work, we first construct a multi-theorem preprocessing NIZK argument from context-hiding homomorphic signatures. In fact, the construction is a designated-prover NIZK. We also show that using homomorphic commitments, we can get statistically sound proofs in the preprocessing and designated-prover models. Together with lattice-based instantiations of homomorphic signatures and commitments, we obtain the first multi-theorem NIZKs in the preprocessing and designated-prover models from standard lattice assumptions. Finally, we show how to generalize our construction to obtain a universally composable NIZK (UC-NIZK) in the preprocessing model from standard lattice assumptions. Our UC-NIZK relies on a simple preprocessing protocol based on a new primitive we call blind homomorphic signatures.

Carsten Baum, Huang Lin, Sabine Oechsner

No abstract is available for this record.

Riccardo Longo

Cryptography is used to protect data and communications.
\nThe basic tools are cryptographic primitives, whose security and efficiency are widely studied.
\nBut in real-life applications these primitives are not used individually, but combined inside complex protocols.
\nThe aim of this thesis is to analyse various cryptographic protocols and assess their security in a formal way.
\nIn chapter 1 the concept of formal proofs of security is introduced and the main categorisation of attack scenarios and types of adversary are presented, and the protocols analysed in the thesis are briefly introduced with some motivation. 
\nIn chapter 2 are presented the security assumptions used in the proofs of the following chapters, distinguishing between the hardness of algebraic problems and the strength of cryptographic primitives.
\nOnce that the bases are given, the first protocols are analysed in chapter 3, where two Attribute Based Encryption schemes are proven secure.
\nFirst context and motivation are introduced, presenting settings of cloud encryption, alongside the tools used to build ABE schemes.
\nThen the first scheme, that introduces multiple authorities in order to improve privacy, is explained in detail and proven secure.
\nFinally the second scheme is presented as a variation of the first one, with the aim of improving the efficiency performing a round of collaboration between the authorities.
\n
\nThe next protocol analysed is a tokenization algorithm for the protection of credit cards.
\nIn chapter 4 the advantages of tokenization and the regulations required by the banking industry are presented, and a practical algorithm is proposed, and proven secure and compliant with the standard. 
\nIn chapter 5 the focus is on the BIX Protocol, that builds a chain of certificates in order to decentralize the role of certificate authorities.
\nFirst the protocol and the structure of the certificates are introduced, then two attack scenarios are presented and the protocol is proven secure in these settings.
\nFinally a viable attack vector is analysed, and a mitigation approach is discussed.
\nIn chapter 6 is presented an original approach on building a public ledger with end-to-end encryption and a one-time-access property, that make it suitable to store sensitive data. 
\nIts security is studied in a variety of attack scenarios, giving proofs based on standard algebraic assumptions. 
\nThe last protocol presented in chapter 7 uses a proof-of-stake system to maintain the consistency of subchains built on top of the Bitcoin blockchain, using only standard Bitcoin transactions.
\nParticular emphasis is given to the analysis of the refund policies employed, proving that the naive approach is always ineffective whereas the chosen policy discourages attackers whose stake falls below a threshold, that may be adjusted varying the protocol parameters.

Hafsa Assidi, Edoukou Berenger Ayebie, El Mamoun Souidi

No abstract is available for this record.

Rafaël del Pino, Vadim Lyubashevsky, Gregor Seiler

We present a group signature scheme, based on the hardness of lattice problems, whose outputs are more than an order of magnitude smaller than the currently most efficient schemes in the literature. Since lattice-based schemes are also usually non-trivial to efficiently implement, we additionally provide the first experimental implementation of lattice-based group signatures demonstrating that our construction is indeed practical -- all operations take less than half a second on a standard laptop. A key component of our construction is a new zero-knowledge proof system for proving that a committed value belongs to a particular set of small size. The sets for which our proofs are applicable are exactly those that contain elements that remain stable under Galois automorphisms of the underlying cyclotomic number field of our lattice-based protocol. We believe that these proofs will find applications in other settings as well. The motivation of the new zero-knowledge proof in our construction is to allow the efficient use of the selectively-secure signature scheme (i.e. a signature scheme in which the adversary declares the forgery message before seeing the public key) of Agrawal et al. (Eurocrypt 2010) in constructions of lattice-based group signatures and other privacy protocols. For selectively-secure schemes to be meaningfully converted to standard signature schemes, it is crucial that the size of the message space is not too large. Using our zero-knowledge proofs, we can strategically pick small sets for which we can provide efficient zero-knowledge proofs of membership.

Elie Kfoury, David Khoury

No abstract is available for this record.

Ilya Grishchenko, Matteo Maffei, Clara Schneidewind

Smart contracts are programs running on cryptocurrency (e.g., Ethereum) blockchains, whose popularity stem from the possibility to perform financial transactions, such as payments and auctions, in a distributed environment without need for any trusted third party. Given their financial nature, bugs or vulnerabilities in these programs may lead to catastrophic consequences, as witnessed by recent attacks. Unfortunately, programming smart contracts is a delicate task that requires strong expertise: Ethereum smart contracts are written in Solidity, a dedicated language resembling JavaScript, and shipped over the blockchain in the EVM bytecode format. In order to rigorously verify the security of smart contracts, it is of paramount importance to formalize their semantics as well as the security properties of interest, in particular at the level of the bytecode being executed. In this paper, we present the first complete small-step semantics of EVM bytecode, which we formalize in the F* proof assistant, obtaining executable code that we successfully validate against the official Ethereum test suite. Furthermore, we formally define for the first time a number of central security properties for smart contracts, such as call integrity, atomicity, and independence from miner controlled parameters. This formalization relies on a combination of hyper- and safety properties. Along this work, we identified various mistakes and imprecisions in existing semantics and verification tools for Ethereum smart contracts, thereby demonstrating once more the importance of rigorous semantic foundations for the design of security verification techniques.

Geoffroy Couteau

Preuves à divulgation nulle de connaissance pour le calcul sécurisé Dans cette thèse, nous étudions les preuves à divulgation nulle de connaissance, une primitive cryptographique permettant de prouver une assertion en ne révélant rien de plus que sa véracité, et leurs applications au calcul sécurisé. Nous introduisons tout d’abord un nouveau type de preuves à divulgation nulle, appelées arguments implicites à divulgation nulle, intermédiaire entre deux notions existantes, les preuves interactives et les preuves non interactives à divulgation nulle. Cette nouvelle notion permet d’obtenir les mêmes bénéfices en terme d’efficacité que les preuves non-interactives dans le contexte de la construction de protocoles de calcul sécurisé faiblement interactifs, mais peut être instanciée à partir des mêmes hypothèses cryptographiques que les preuves interactives, permettant d’obtenir de meilleures garanties d’efficacité et de sécurité. Dans un second temps, nous revisitons un système de preuves à divulgation nulle de connaissance qui est particulièrement utile dans le cadre de protocoles de calcul sécurisé manipulant des nombres entiers, et nous démontrons que son analyse de sécurité classique peut être améliorée pour faire reposer ce système de preuve sur une hypothèse plus standard et mieux connue. Enfin, nous introduisons une nouvelle méthode de construction de systèmes de preuves à divulgation nulle sur les entiers, qui représente une amélioration par rapport aux méthodes existantes, tout particulièrement dans un modèle de type client-serveur, où un client à faible puissance de calcul participe à un protocole de calcul sécurisé avec un serveur à forte puissance de calcul.

Alican Beydemir, İbrahim Soğukpınar

Importance of Internet of Things technologies increased in recent years. However, these technologies carry some security vulnerabilities because of their network communication layer. The root cause of these vulnerabilities is usually the Authentication problem. Zero knowledge proof method is a strong cryptographic solution for Authentication problem that is proving of having a knowledge to another party without revealing anything other than the veracity of the statement. Zero knowledge proof method is consist of two-way complex mathematical algorithms for both parties. In this work, a new method that uses zero knowledge proofs has been proposed to provide efficient solution for Internet of Things technologies. New method was implemented and tested, then compared with existing proposed zero knowledge proof based authentication methods.

Gewu Bu, Maria Potop-Butucaru

In this paper, we propose BAN-GZKP that optimizes the best to date secure lightweight and energy efficient authentication scheme, BANZKP, designed for WBAN networks. BANZKP is vulnerable to several security attacks such as the replay attack, DDoS attacks at sink and redundancy information crack. Also BANZKP needs an end-to-end authentication which is not compliant with the human body postural mobility. Our scheme, BAN-GZKP, improves both the security and postural mobility resilience of BANZKP. In order to fix the security vulnerabilities of BANZKP, BAN-GZKP uses a novel random key allocation. Moreover, BAN-GZKP uses a hop-by-hop authentication scheme which makes it tolerant to postural mobility. We further prove the reliability of our scheme to various attacks including those to which BANZKP is vulnerable. Furthermore, via extensive simulations we prove that our scheme, BAN-GZKP, outperforms BANZKP in terms of reliability to human body postural mobility for various network parameters (end-to-end delay, number of packets exchanged in the network, number of transmissions). We compared both schemes using representative convergecast strategies with various transmission rates and human postural mobility. When our BAN-GZKP scheme is used the percentage of packets received increases by 34.06%, the end-to-end-delay reduces by 36.02% and the number of transmissions reduces by 8.75% with respect to the case when BANZKP is used. Moreover, BAN-GZKP uses only a three-phase authentication which is optimal in the class of ZKP protocols. Finally, it is important to mention that BAN-GZKP has no additional cost in terms memory, computational complexity or energy consumption compared to BANZKP.

Ao Lei, Haitham Cruickshank, Yue Cao, Philip Asuquo · 6 authors

As modern vehicle and communication technologies advanced apace, people begin to believe that the Intelligent Transportation System (ITS) would be achievable in one decade. ITS introduces information technology to the transportation infrastructures and aims to improve road safety and traffic efficiency. However, security is still a main concern in vehicular communication systems (VCSs). This can be addressed through secured group broadcast. Therefore, secure key management schemes are considered as a critical technique for network security. In this paper, we propose a framework for providing secure key management within the heterogeneous network. The security managers (SMs) play a key role in the framework by capturing the vehicle departure information, encapsulating block to transport keys and then executing rekeying to vehicles within the same security domain. The first part of this framework is a novel network topology based on a decentralized blockchain structure. The blockchain concept is proposed to simplify the distributed key management in heterogeneous VCS domains. The second part of the framework uses the dynamic transaction collection period to further reduce the key transfer time during vehicles handover. Extensive simulations and analysis show the effectiveness and efficiency of the proposed framework, in which the blockchain structure performs better in term of key transfer time than the structure with a central manager, while the dynamic scheme allows SMs to flexibly fit various traffic levels.

Alex Escala Ribas

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.

Chien-Nan Wu, Chun‐I Fan, Jheng-Jia Huang, Yi‐Fan Tseng · 5 authors

No abstract is available for this record.

Nazri bin Abdullah, Anne Håkansson, Esmiralda Moradian

Existing authentication protocols for Big Data system such as Apache Hadoop is based on Kerberos. In the Kerberos protocol, there are numerous security issues that have remained unsolved; replay attacks, DDoS and single point of failure are some examples. These indicate potential security vulnerabilities and Big Data risks in using Hadoop. This paper presents drawbacks of Kerberos implementations and identifies authentication requirements that can enhance the security of Big Data in distributed environments. The enhancement proposed is based on the rising technology of blockchain that overcomes shortcomings of Kerberos.

LI Zichen,LIU Boya,WANG Peidong,YANG Yatao

To ensure the wireless communication security of the reader and tag in the Radio Frequency Identification(RFID) system,based on domestic public key cryptography algorithm SM2 and introducing zero knowledge proof idea,this paper proposes a two-way authentication protocol.Then security and efficiency analysis are given.The formal analysis is made by using BAN logic.Results show that the two-way authentication of the proposed protocol is completed in the case that reader and tag just interact twice,and has high safety and communication efficiency.

Wided Boubakri, Walid Abdallah, Noureddine Boudriga

5G mobile communication is being designed as heterogeneous network where different platforms, several technologies, and various cell sizes are deployed to fit specific requirements in terms of data rates and latency. The heterogeneity nature of this network will lead to new security issues and threats, especially when the number of deployed mobile devices become very important. In this paper, we propose a simple PKI certificate based access control scheme that is implemented on a multi-layer communication architecture designed for 5G networks. In addition, we establish a scalable authentication and handover schemes that can ensure security within the network. To this purpose, we define various types of certificates with different features and utilization. The authentication scheme is based on zero knowledge proof (ZKP) and is used to achieve secure device registration procedure before generating authorization certificates that will be used to enable secure device-to-device communication. We use simulation work to assess the efficiency of our scheme in terms of total overhead and average latency. Performance evaluation results show that our scheme is more scalable than existing authentication and handover schemes.