Blockchain Papers

Kang Li, Rupeng Yang, Man Ho Au, Qiuliang Xu

No abstract is available for this record.

Yanqi Zhao, Yannan Li, Qilin Mu, Bo Yang · 5 authors

The cyber physical system (CPS) has gained considerable success in large-scale distributed integration environment. In such systems, the sensor devices collect data which would be disseminated via reliable manner to all interested co-operant entities from the physical world. However, highly unreliable environment of CPS, for example, a number of limitations of existing network middle wares, makes secure and reliable data distribution services a challenge issue. In this paper, we propose a new architecture called secure pub-sub (SPS) without middle ware, i.e., blockchain-based fair payment with reputation. In SPS, publishers publish a topic on the blockchain and subscribers specify an interest message by making a deposit to subscribing the topic. Then, if the interest message matches the topic, the publisher transmits the encrypted content of the topic to the blockchain such that the subscribers can decrypt the ciphertext to obtain the content, and mark the publisher as its reputation. Finally, the publisher receives the payment from the subscriber. The new proposal provides confidentiality and reliability of data, anonymity of subscribers and payment fairness between the publishers and subscribers. Different from the traditional pub-sub services, no trusted third party is involved in our system due to employing blockchain technique. The security of the proposed SPS is analyzed as well. The implementation of the protocol on Ethereum of smart contract demonstrates the validity of SPS.

Danni Wang, Juntao Gao, Haiyong Yu, Xuelian Li

No abstract is available for this record.

Duc-Hiep Nguyen, Dinh-Nghia Nguyen-Duc, Nguyen Huynh Tuong, Hoang-Anh Pham

By using a decentralized peer-to-peer network together with public and distributed ledger to decentralize the central authority, Blockchain has shown its great potential with the success of Bitcoin. However, the blockchain technology can go beyond financial transactions. In this paper, we propose an approach that utilizes the blockchain technology to issue immutable digital certificates and improve the current limitations of the existing certificate verifying systems such as faster, more trusted, and independent of the central authority. Our prototype has been successfully deployed for several short-term courses at the Center of Computer Engineering, HCMC University of Technology, Vietnam. This result indicates that our proposed system is an appropriate solution adopting ICT for e-government, especially in certificate and diploma management.

Yunru Zhang, Debiao He, Kim‐Kwang Raymond Choo

Internet of Things (IoT) and cloud computing are increasingly integrated, in the sense that data collected from IoT devices (generally with limited computational and storage resources) are being sent to the cloud for processing, etc., in order to inform decision making and facilitate other operational and business activities. However, the cloud may not be a fully trusted entity, like leaking user data or compromising user privacy. Thus, we propose a privacy‐preserving and user‐controlled data sharing architecture with fine‐grained access control, based on the blockchain model and attribute‐based cryptosystem. Also, the consensus algorithm in our system is the Byzantine fault tolerance mechanism, rather than Proof of Work.

Tuyet Duong, Alexander Chepurnoy, Hong-Sheng Zhou

In the past years, the security of Bitcoin-like protocols has been intensively studied. However, previous investigations are mainly focused on the single-mode version of Bitcoin protocol, where the protocol is running among full nodes (miners). In this paper we initiate the study of multi-mode cryptocurrency protocols. We generalize the recent framework by Garay et al (Eurocrypt 2015) with new security de nitions that capture the security of realistic cryptocurrency systems. e.g. Bitcoin with full and lightweight nodes. As an immediate application of our new framework, we analyze the security of existing blockchain pruning proposals for Bitcoin and Ethereum aiming to improve the storage e ciency of network nodes by pruning unnecessary information from the ledger.

Samvit Jain, Edward W. Felten, Steven Goldfeder

Online and offline storage of digital currency present conflicting risks for a Bitcoin exchange. While bitcoins stored on online devices are continually vulnerable to malware and other network-based attacks, offline reserves are endangered on access, as transferring bitcoins requires the exposure of otherwise encrypted and secured private keys. In particular, fluctuations in customer demand for deposited bitcoin require exchanges to periodically refill online storage systems with bitcoins held offline. This raises the natural question of what upper limit on online reserves minimizes losses due to theft over time. In this article, we investigate this optimization problem, developing a model that predicts the optimal ceiling on online reserves, given average rates of deposits, withdrawals, and theft. We evaluate our theory with an event-driven simulation of the setup, and find that our equation yields a numerical value for the threshold that differs by less than 2% from experimental results. We conclude by considering open questions regarding more complex storage architectures.

Fangyu Gai, Baosheng Wang, Wenping Deng, Wei Peng

No abstract is available for this record.

Ben Berger, Zvika Brakerski

No abstract is available for this record.

Georg Fuchsbauer, Eike Kiltz, Julian Loss

No abstract is available for this record.

Eli Ben‐Sasson, Alessandro Chiesa, Michael Riabzev, Nicholas Spooner · 6 authors

We design, implement, and evaluate a zero knowledge succinct non-interactive argument (SNARG) for Rank-1 Constraint Satisfaction (R1CS), a widely-deployed NP language undergoing standardization. Our SNARG has a transparent setup, is plausibly post-quantum secure, and uses lightweight cryptography. A proof attesting to the satisfiability of n constraints has size \(O(\log ^2 n)\); it can be produced with \(O(n \log n)\) field operations and verified with O(n). At 128 bits of security, proofs are less than \({250}\,\mathrm{kB}\) even for several million constraints, more than \(10{\times }\) shorter than prior SNARGs with similar features.

Yunlei Zhao

No abstract is available for this record.

Hyungmin Cho

Blockchain technology rapidly gained popularity based on its open and decentralized operation. Consensus protocol is the core mechanism of a blockchain network that securely maintains the distributed ledger from possible attacks from adversaries. Proof-of-work (PoW) is a commonly used consensus protocol that requires a significant amount of computation to find a new valid block. As the application-specific integrated circuits (ASICs) that are specially designed for PoW computation begin to dominate blockchain consensus operation, the decentralized nature of blockchain networks is being threatened. Many PoW mechanisms are being proposed to disincentivize the use of ASICs in the consensus operation. Employing multiple hash functions in the PoW computation (i.e., multi-hash PoW) is one of the commonly adopted approaches to achieve such ASIC-resistance. In this paper, we experimentally evaluate the level of ASIC-resistance of the multi-hash PoW mechanisms. We assess the level of ASIC-resistance based on the performance gap between ASICs and general-purpose computing platforms. Contrary to the expectation of the multi-hash PoW mechanisms, our results reveal that ASIC-resistance of these PoW mechanisms is not strong enough to prevent ASIC-based mining. Most of them show similar levels of ASIC-resistance as those of PoW mechanisms that are already defeated by ASIC-based systems.

Chaya Ganesh, Yashvanth Kondi, Arpita Patra, Pratik Sarkar

No abstract is available for this record.

Eli Ben‐Sasson, Iddo Bentov, Yinon Horesh, Michael Riabzev

The family of Reed-Solomon (RS) codes plays a prominent role in the construction of quasilinear probabilistically checkable proofs (PCPs) and interactive oracle proofs (IOPs) with perfect zero knowledge and polylogarithmic verifiers. The large concrete computational complexity required to prove membership in RS codes is one of the biggest obstacles to deploying such PCP/IOP systems in practice. To advance on this problem we present a new interactive oracle proof of proximity (IOPP) for RS codes; we call it the Fast RS IOPP (FRI) because (i) it resembles the ubiquitous Fast Fourier Transform (FFT) and (ii) the arithmetic complexity of its prover is strictly linear and that of the verifier is strictly logarithmic (in comparison, FFT arithmetic complexity is quasi-linear but not strictly linear). Prior RS IOPPs and PCPs of proximity (PCPPs) required super-linear proving time even for polynomially large query complexity. For codes of block-length N, the arithmetic complexity of the (interactive) FRI prover is less than 6 * N, while the (interactive) FRI verifier has arithmetic complexity <= 21 * log N, query complexity 2 * log N and constant soundness - words that are delta-far from the code are rejected with probability min{delta * (1-o(1)),delta_0} where delta_0 is a positive constant that depends mainly on the code rate. The particular combination of query complexity and soundness obtained by FRI is better than that of the quasilinear PCPP of [Ben-Sasson and Sudan, SICOMP 2008], even with the tighter soundness analysis of [Ben-Sasson et al., STOC 2013; ECCC 2016]; consequently, FRI is likely to facilitate better concretely efficient zero knowledge proof and argument systems. Previous concretely efficient PCPPs and IOPPs suffered a constant multiplicative factor loss in soundness with each round of "proof composition" and thus used at most O(log log N) rounds. We show that when delta is smaller than the unique decoding radius of the code, FRI suffers only a negligible additive loss in soundness. This observation allows us to increase the number of "proof composition" rounds to Theta(log N) and thereby reduce prover and verifier running time for fixed soundness.

Jonathan Bootle, Jens Groth

No abstract is available for this record.

Haibo Tian, Liqing Fu, Jiejie He

No abstract is available for this record.

Wang Yu-xiao, Juntao Gao

In Bitcoin financial system, a user’s privacy is supposed to be protected by means of anonymity. However, the anonymity makes illegal trades possible because nobody is able to reveal the real identities of the illegal users. In this paper, we propose a regulation scheme based on the ciphertext-policy hierarchical attribute-based encryption (CP-HABE). In the scheme, users’ identities are encrypted by using access policy and are contained in their transaction. A type of user is defined as the dependable regulation node, which is responsible for the regulation of transactions and encrypted identities. A new signature algorithm instead of the elliptic curve signature is adopted to generate wallet key pairs, this establishes a connection between wallet addresses and encrypted identities. When a transaction is doubted to involve illegal activities, the authorized regulation nodes are capable of revealing the users’ real identities and add the illegal identities to a public blacklist. Our system is based on a new CP-HABE scheme which is proved to be secure against chosen-plaintext attack in the standard model under the Bilinear Diffie–Hellman Exponent assumption. Finally, we give a performance analysis of our system. The proposed regulation system can reveal criminals’ identities undertaking illegal activities.

Abdallah Zoubir Ourad, Boutheyna Belgacem, Khaled Salah

No abstract is available for this record.

Fabrice Benhamouda, Olivier Blazy, Léo Ducas, Willy Quach

No abstract is available for this record.

Benoît Libert, San Ling, Khoa Nguyen, Huaxiong Wang

No abstract is available for this record.

Carsten Baum, Jonathan Bootle, Andrea Cerulli, Rafaël del Pino · 6 authors

No abstract is available for this record.

Riccardo Longo

Cryptography is used to protect data and communications.&#13;\nThe basic tools are cryptographic primitives, whose security and efficiency are widely studied.&#13;\nBut in real-life applications these primitives are not used individually, but combined inside complex protocols.&#13;\nThe aim of this thesis is to analyse various cryptographic protocols and assess their security in a formal way.&#13;\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. &#13;\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.&#13;\nOnce that the bases are given, the first protocols are analysed in chapter 3, where two Attribute Based Encryption schemes are proven secure.&#13;\nFirst context and motivation are introduced, presenting settings of cloud encryption, alongside the tools used to build ABE schemes.&#13;\nThen the first scheme, that introduces multiple authorities in order to improve privacy, is explained in detail and proven secure.&#13;\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.&#13;\n&#13;\nThe next protocol analysed is a tokenization algorithm for the protection of credit cards.&#13;\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. &#13;\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.&#13;\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.&#13;\nFinally a viable attack vector is analysed, and a mitigation approach is discussed.&#13;\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. &#13;\nIts security is studied in a variety of attack scenarios, giving proofs based on standard algebraic assumptions. &#13;\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.&#13;\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.

Jianting Ning, Hung Dang, Ruomu Hou, Ee‐Chien Chang

No abstract is available for this record.