Blockchain Papers

S. M. Ratseev, M. A. Rostov

, , , , 432017, ,

E. O. Kiktenko, M. A. Kudinov, A. K. Fedorov

Blockchain is a distributed ledger, which is protected against malicious modifications by means of cryptographic tools, e.g. digital signatures and hash functions. One of the most prominent applications of blockchains is cryptocurrencies, such as Bitcoin. In this work, we consider a particular attack on wallets for collecting assets in a cryptocurrency network based on brute-force search attacks. Using Bitcoin as an example, we demonstrate that if the attack is implemented successfully, a legitimate user is able to prove that fact of this attack with a high probability. We also consider two options for modification of existing cryptocurrency protocols for dealing with this type of attacks. First, we discuss a modification that requires introducing changes in the Bitcoin protocol and allows diminishing the motivation to attack wallets. Second, an alternative option is the construction of special smart-contracts, which reward the users for providing evidence of the brute-force attack. The execution of this smart-contract can work as an automatic alarm that the employed cryptographic mechanisms, and (particularly) hash functions, have an evident vulnerability.

Dimaz Ankaa Wijaya, Joseph K. Liu, Ron Steinfeld, Dongxi Liu

Monero is one of the privacy-preserving cryptocurrencies employing CryptoNote protocol. The privacy features in Monero are provided by cryptographic techniques such as linkable ring signature and one-time public key. Recent studies show that the majority of Monero inputs are traceable prior to mandatory RingCT transaction. After the RingCT was implemented, the problems were mitigated. We propose a novel attack to reduce the anonymity of Monero transactions or even to fully deanonymise the inputs. The proposed protocol can be launched in RingCT protocol and enables multiple attackers to collaborate without trusting each other. The attack scheme can be planted in the existing Monero services without extra fees and without putting the users' money at risk.

Nisha Malik, Priyadarsi Nanda, Arushi Arora, Xiangjian He · 5 authors

Authentication and revocation of users in Vehicular Adhoc Networks (VANETS) are two vital security aspects. It is extremely important to perform these actions promptly and efficiently. The past works addressing these issues lack in mitigating the reliance on the centralized trusted authority and therefore do not provide distributed and decentralized security. This paper proposes a blockchain based authentication and revocation framework for vehicular networks, which not only reduces the computation and communication overhead by mitigating dependency on a trusted authority for identity verification, but also speedily updates the status of revocated vehicles in the shared blockchain ledger. In the proposed framework, vehicles obtain their Pseudo IDs from the Certificate Authority (CA), which are stored along with their certificate in the immutable authentication blockchain and the pointer corresponding to the entry in blockchain, enables the Road Side Units (RSUs) to verify the identity of a vehicle on road. The efficiency and performance of the framework has been validated using the Omnet++ simulation environment.

Mohamed Amine Ferrag, Makhlouf Derdour, Mithun Mukherjee, Abdelouahid Derhab · 6 authors

This paper presents a comprehensive survey of the existing blockchain protocols for the Internet of Things (IoT) networks. We start by describing the blockchains and summarizing the existing surveys that deal with blockchain technologies. Then, we provide an overview of the application domains of blockchain technologies in IoT, e.g., Internet of Vehicles, Internet of Energy, Internet of Cloud, Edge computing, etc. Moreover, we provide a classification of threat models, which are considered by blockchain protocols in IoT networks, into five main categories, namely identity-based attacks, manipulation-based attacks, cryptanalytic attacks, reputation-based attacks, and service-based attacks. In addition, we provide a taxonomy and a side-by-side comparison of the state-of-the-art methods toward secure and privacy-preserving blockchain technologies with respect to the blockchain model, specific security goals, performance, limitations, computation complexity, and communication overhead. Based on the current survey, we highlight open research challenges and discuss possible future research directions in the blockchain technologies for IoT.

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.

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.

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.

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.

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.

Byeong-ju Park, Tae‐Jin Lee, Jin Kwak

ICT 기술이 발달하며 IoT 환경이 주목받고 있다. 하지만 IoT 디바이스는 다양한 사용 용도만큼 디바이스가 동작하는 CPU의 성능도 다양하지만, 인증에 필요한 암호화가 내장되지 않은 CPU를 사용하거나, 공개키 암호가 동작하지 않는 디바이스도 다수 존재한다. 이에 따라, 본 논문에서는 램포트 해시체인, 램포트 서명, 블록체인을 분석하고, 기존 인증 프로토콜 분석을 통해 인증, 무결성 및 부인 방지 기능을 제공하는 블록체인 기반 IoT 디바이스 인증 스킴을 제안하였다. 본 논문에서 제안하는 스킴은 IoT 디바이스에 단순 해시연산만을 요구하여 저성능 IoT 디바이스에서도 동작이 가능해 IoT 환경에서 안전한 인증을 보장할 수 있다. With ICT technology develops, IoT environment is attracting attention. However, IoT devices have various CPU performance as much as various purpose of use. Some IoT devices use the cpu that doesn't support public key cryptogrphy or crypto acceleration. In this paper, we study Blockchain-based IoT Device Authentication Scheme that provides authentication, integirity and non-repudation through analysis of Lamport Hash-chain, Lamport Signature, Blockchain and existing Authentication protocols. The proposed scheme requires only simple hash operation in IoT devices and it can operate in low performance IoT device, thus ensuring secure authentication in IoT environment.

Marjan Škrobot

The main purpose of Password-Authenticated Key Exchange (PAKE) is to allow secure authenticated communication over insecure networks between two or more parties who only share a low-entropy password. It is common practice that the secret key derived from a PAKE execution is used to authenticate and encrypt some data payload using symmetric key protocols. Unfortunately, most PAKEs of practical interest, including three protocols considered in this thesis, are studied using so-called game-based models, which -- unlike simulation models -- do not guarantee secure composition per se. However, Brzuska et al. (CCS 2011) have shown that a middle ground is possible in the case of authenticated key exchange that relies on Public-Key Infrastructure (PKI): the game-based models do provide secure composition guarantees when the class of higher-level applications is restricted to symmetric-key protocols. The question that we pose in this thesis is whether or not a similar result can be exhibited for PAKE. Our work answers this question positively. More specifically, we show that PAKE protocols secure according to the game-based Real-or-Random (RoR) definition of Abdalla et al. (PKC 2005) allow for automatic, secure composition with arbitrary, higher-level symmetric key protocols. Since there is evidence that most PAKEs secure in the Find-then-Guess (FtG) model of Bellare et al. (EUROCRYPT 2000) are in fact secure according to the RoR definition, we can conclude that nearly all provably secure PAKEs enjoy a certain degree of composition, one that at least covers the case of implementing secure channels. Although many different protocols that accomplish PAKE have been proposed over last two decades, only a few newcomers managed to find their way to real world applications - albeit lacking an intense and prolonged public scrutiny. As a step in the direction of providing one, this dissertation considers the security and efficiency of two relatively recently proposed PAKE protocols - Dragonfly and J-PAKE. In particular, we prove the security of a very close variant of Dragonfly employing the standard FtG model which incorporates forward secrecy. Thus, our work confirms that Dragonfly's main flows are sound. Furthermore, we contribute to the discussion by proposing and examining (in the RoR model of security) two variants of J-PAKE - which we call RO-J-PAKE and CRS-J-PAKE - that each makes the use of two less zero-knowledge proofs than the original protocol, at the cost of an additional security assumption. Our work reveals that CRS-J-PAKE has an edge in terms of efficiency over J-PAKE for both standard group choices: subgroups of finite fields and elliptic curves. The same is true for RO-J-PAKE, but only when instantiated with elliptic curves.

Olivier Blazy, Céline Chevalier, Paul Germouty

No abstract is available for this record.

Roberto Metere, Changyu Dong

Aiming for strong security assurance, recently there has been an increasing interest in formal verification of cryptographic constructions. This paper presents a mechanised formal verification of the popular Pedersen commitment protocol, proving its security properties of correctness, perfect hiding, and computational binding. To formally verify the protocol, we extended the theory of EasyCrypt, a framework which allows for reasoning in the computational model, to support the discrete logarithm and an abstraction of commitment protocols. Commitments are building blocks of many cryptographic constructions, for example, verifiable secret sharing, zero-knowledge proofs, and e-voting. Our work paves the way for the verification of those more complex constructions.

Thanh Bui, Tuomas Aura

Blockchains and other public ledger structures promise a new way to create globally consistent event logs and other records. We make use of this consistency property to detect and prevent man-in-the-middle attacks in a key exchange such as Diffie-Hellman or ECDH. Essentially, the MitM attack creates an inconsistency in the world views of the two honest parties, and they can detect it with the help of the ledger. Thus, there is no need for prior knowledge or trusted third parties apart from the distributed ledger. To prevent impersonation attacks, we require user interaction. It appears that, in some applications, the required user interaction is reduced in comparison to other user-assisted key-exchange protocols.

Daniel Augot, Hervé Chabanne, Thomas Chenevier, William R. George · 5 authors

We present an identity management scheme built into the Bitcoin blockchain, allowing for identities that are as indelible as the blockchain itself. Moreover, we take advantage of Bitcoin's decentralized nature to facilitate a shared control between users and identity providers, allowing users to directly manage their own identities, fluidly coordinating identities from different providers, even as identity providers can revoke identities and impose controls.

Tomaso Aste, Paolo Tasca, Tiziana Di Matteo

The authors describe blockchain's fundamental concepts, provide perspectives on its challenges and opportunities, and trace its origins from the Bitcoin digital cash system to recent applications.

Abrahim Ladha, Sharbani Pandit, Sanya Ralhan

Ethereum represents new innovation in the fields of cryptocurrency which has become relatively stagnate, promising many things, including an entire programming language and development enviroment built into the network. However the current trend is to write implementations and proof of concepts before doing the rigor involved with proving security. Miller's recent thesis is an attempt to remedy this, and we apply his provable security techniques to the algorithm description of CASPER, the new "proof-of-stake" consensus protocol scheme to be implemented in ethereum. We conclude by stating it satisfies almost all the definitions, except one, leaving room for improvement.