Blockchain Papers

Georg Fuchsbauer

No abstract is available for this record.

Xiaoyi Yang, Meijuan Huang

Distributed networks remarkably enhance the convenience of network connectivity. How to achieve efficient cooperative computation while preserving data privacy is a challenge in the scenario of distributed networks. Secure computation, as the key technology of information security and privacy protection in the distributed networks, attracts more and more attention. In the paper, we develop the protocols of secure two-party computation in the presence of malicious adversaries which are constructed with homomorphic probabilistic cryptosystem, and propose four honest-verifier zero-knowledge proof protocols to detect two cheating behaviours of the malicious adversary. The proposed protocols are more targeted than the existing work. The analysis shows that the proposed protocols are complete, sound and zero-knowledge. As an application, we show how to use our protocols in a secure two-party protocol to detect cheating, which can make it secure in the presence of malicious adversaries.

Thach Ngoc Nguyen, Christian Servín, Владик Крейнович

Nowadays, most financial transactions are based on a centralized system, when all the transaction records are stored in a central location. This centralization makes the financial system vulnerable to cyber-attacks. A natural way to make the financial system more robust and less vulnerable is to switch to decentralized currencies. Such a transition will also make financial system more transparent. Historically first currency of this type -- bitcoin -- use a large amount of electric energy to mine new coins and is, thus, not scalable to the level of financial system as a whole. A more realistic and less energy-consuming scheme is provided by proof-of-stake currencies, where the right to mint a new coin is assigned to a randomly selected user, with probability depending of the user's stake (e.g., his/her number of coins). What probabilities should we choose? In this paper, we find the probability selection that provides the optimal result -- optimal in the sense that it is the least inductive to cheating.

Nikos Fotiou, Vasilios A. Siris, George C. Polyzos

Despite technological advances, most smart objects in the Internet of Things (IoT) cannot be accessed using technologies designed and developed for interacting with powerful Internet servers. IoT use cases involve devices that not only have limited resources, but also they are not always connected to the Internet and are physically exposed to tampering. In this paper, we describe the design, development, and evaluation of a smart contract-based solution that allows end-users to securely interact with smart devices. Our approach enables access control, Thing authentication, and payments in a fully decentralized setting, taking at the same time into consideration the limitations and constraints imposed by both blockchain technologies and the IoT paradigm. Our prototype implementation is based on existing technologies, i.e., Ethereum smart contracts, which makes it realistic and fundamentally secure.

Bingsheng Zhang, Roman Oliynykov, Hamed Balogun

A treasury system is a community-controlled and decentralized collaborative decision-making mechanism for sustainable funding of blockchain development and maintenance. During each treasury period, project proposals are submitted, discussed, and voted for; top-ranked projects are funded from the treasury. The Dash governance system is a real-world example of such kind of systems. In this work, we, for the first time, provide a rigorous study of the treasury system. We modelled, designed, and implemented a provably secure treasury system that is compatible with most existing blockchain infrastructures, such as Bitcoin, Ethereum, etc. More specifically, the proposed treasury system supports liquid democracy/delegative voting for better collaborative intelligence. Namely, the stake holders can either vote directly on the proposed projects or delegate their votes to experts. Its core component is a distributed universally composable secure end-to-end verifiable voting protocol. The integrity of the treasury voting decisions is guaranteed even when all the voting committee members are corrupted. To further improve efficiency, we proposed the world's first honest verifier zero-knowledge proof for unit vector encryption with logarithmic size communication. This partial result may be of independent interest to other cryptographic protocols. A pilot system is implemented in Scala over the Scorex 2.0 framework, and its benchmark results indicate that the proposed system can support tens of thousands of treasury participants with high efficiency.

Joachim Zahnentferner

No abstract is available for this record.

Konstantinos Chalkias, James Brown, Mike Hearn, Tommy Lillehagen · 6 authors

Inspired by the blockchain architecture and existing Merkle tree based signature schemes, we propose BPQS, an extensible post-quantum (PQ) resistant digital signature scheme best suited to blockchain and distributed ledger technologies (DLTs). One of the unique characteristics of the protocol is that it can take advantage of application-specific chain/graph structures in order to decrease key generation, signing and verification costs as well as signature size. Compared to recent improvements in the field, BPQS outperforms existing hash-based algorithms when a key is reused for reasonable numbers of signatures, while it supports a fallback mechanism to allow for a practically unlimited number of signatures if required. We provide an open source implementation of the scheme and benchmark it.

Ilya Sukhodolskiy, Sergey Zapechnikov

In this paper, we present a prototype of multi-user system for access control to datasets stored in an untrusted cloud environment. Cloud storage like any other untrusted environment needs the ability to secure share information. Our approach provides an access control over the data stored in the cloud without the provider participation. The main tool of access control mechanism is ciphertext-policy attribute-based encryption scheme with dynamic attributes. Using a blockchain-based decentralized ledger, our system provides immutable log of all meaningful security events, such as key generation, access policy assignment, change or revocation, access request. We propose a set of cryptographic protocols ensuring privacy of cryptographic operations requiring secret or private keys. Only ciphertexts of hash codes are transferred through the blockchain ledger. The prototype of our system is implemented using smart contracts and tested on Ethereum blockchain platform.

Sepideh Avizheh, Reihaneh Safavi–Naini, Siamak F. Shahandashti

BIP70 is the Bitcoin payment protocol for communication between a merchant and a pseudonymous customer. McCorry et al. (FC~2016) showed that BIP70 is prone to refund attacks and proposed a fix that requires the customer to sign their refund request. They argued that this minimal change will provide resistance against refund attacks. In this paper, we point out the drawbacks of McCorry et al.'s fix and propose a new approach for protection against refund attacks using the Bitcoin multi-signature mechanism. Our solution does not rely on merchants storing refund requests, and unlike the previous solution, allows updating refund addresses through email. We discuss the security of our proposed method and compare it with the previous solution. We also propose a novel application of our refund mechanism in providing anonymity for payments between a payer and payee in which merchants act as mixing servers. We finally discuss how to combine the above two mechanisms in a single payment protocol to have an anonymous payment protocol secure against refund attacks.

Xinxin Fan

Stealth address prevents public association of a blockchain transaction's output with a recipient's wallet address and hides the actual destination address of a transaction. While stealth address provides an effective privacy-enhancing technology for a cryptocurrency network, it requires blockchain nodes to actively monitor all the transactions and compute the purported destination addresses, which restricts its application for resource-constrained environments like Internet of Things (IoT). In this paper, we propose DKSAP-IoT, a faster dual-key stealth address protocol for blockchain-based IoT systems. DKSAP-IoT utilizes a technique similar to the TLS session resumption to improve the performance and reduce the transaction size at the same time between two communication peers. Our theoretical analysis as well as the extensive experiments on an embedded computing platform demonstrate that DKSAP-IoT is able to reduce the computational overhead by at least 50% when compared to the state-of-the-art scheme, thereby paving the way for its application to blockchain-based IoT systems.

Jonathan Bootle, Andrea Cerulli, Jens Groth, S. Jakobsen · 5 authors

No abstract is available for this record.

Jonathan Katz, Vladimir Kolesnikov, Xiao Wang

Recent work, including ZKBoo, ZKB++, and Ligero, has developed efficient non-interactive zero-knowledge proofs of knowledge (NIZKPoKs) for Boolean circuits based on symmetric-key primitives alone, using the "MPC-in-the-head" paradigm of Ishai et al. We show how to instantiate this paradigm with MPC protocols in the preprocessing model; once optimized, this results in an NIZKPoK with shorter proofs (and comparable computation) as in prior work for circuits containing roughly 300--100,000 AND~gates. In contrast to prior work, our NIZKPoK also supports witness-independent preprocessing, which allows the prover to shift most of its work to an offline phase before the witness is known. We use our NIZKPoK to construct a signature scheme based only on symmetric-key primitives (and hence with "post-quantum" security). The resulting scheme has shorter signatures than the scheme built using ZKB++ (and comparable signing/verification time), and is even competitive with hash-based signature schemes. To further highlight the flexibility and power of our NIZKPoK, we also use it to build efficient ring and group signatures based on symmetric-key primitives alone. To our knowledge, the resulting schemes are the most efficient constructions of these primitives that offer post-quantum security.

Parthajit Roy

No abstract is available for this record.

Christos Patsonakis, Katerina Samari, Mema Roussopoulos, Aggelos Kiayias

Public-key infrastructures (PKIs) are an integral part of the security foundations of digital communications. Their widespread deployment has allowed the growth of important applications, such as, internet banking and e-commerce. Centralized PKIs (CPKIs) rely on a hierarchy of trusted Certification Authorities (CAs) for issuing, distributing and managing the status of digital certificates, i.e., unforgeable data structures that attest to the authenticity of an entity’s public key. Unfortunately, CPKI’s have many downsides in terms of security and fault tolerance and there have been numerous security incidents throughout the years. Decentralized PKIs (DPKIs) were proposed to deal with these issues as they rely on multiple, independent nodes. Nevertheless, decentralization raises other concerns such as what are the incentives for the participating nodes to ensure the service’s availability.

Kuo‐Hui Yeh, Chunhua Su, Jia-Li Hou, Wayne Chiu · 5 authors

Recently, the popularity and universality of smart-devices has led to rapid advancement in the development of applications for mobile commerce around the world. Novel mobile payment schemes, such as Apple pay, Android pay, and Samsung pay are becoming an increasingly popular ways to conduct online transactions, no matter what type of smart devices are used. Due to the attendant growth in the importance of security, significant attention has been devoted to the challenge of designing and implementing a robust mobile payment scheme for securing online transactions. In this paper, we demonstrate a robust mobile payment scheme based on sturdy certificateless signatures with bilinear pairing. We elegantly refine the proposed mobile payment scheme to make it suitable for computation-constrained mobile devices. The practicability of the proposed mobile payment scheme is then certified via a rigorous security analysis and thorough performance evaluation using the Raspberry PI as the implementation platform for our proposed scheme. Furthermore, we implement a transaction repository with the aid of smart contract technology. The simulation results, based on Ethereum, demonstrate the feasibility of employing the smart contract technology to secure mobile payments.

Geoffrey Goodell, Tomaso Aste

Modern retail banking creates a kind of panopticon for consumer behaviour, ultimately promising to implement a mechanism that binds all of the financial activities undertaken by an individual to a single, unitary identity. In the age of Big Data, consumers have legitimate reasons to resist such surveillance, particularly in cases wherein monitoring is carried out without their knowledge and judgments based upon such monitoring are used to disincentivise or punish legitimate activities. The risk to consumers increases with the ever-increasing share of financial transactions that are performed electronically. Cryptocurrencies offer an alternative to traditional methods of electronic value exchange, promising anonymous, cash-like electronic transfers, but in practice they fall short for several key reasons. We consider the false choice between total surveillance, as represented by banking as currently implemented by institutions, and impenetrable lawlessness, as represented by privacy-enhancing cryptocurrencies as currently deployed. We identify a range of alternatives between those two extremes, and we consider two potential compromise approaches that offer both the auditability required for regulators and the anonymity required for users

Fatemeh Rezaeibagha, Yi Mu, JH Cho

Cryptocurrencies based on blockchain infrastructures have shown their advantages such as double-spending resistance and decentralization. Each transaction of cryptocurrency requires a certain amount of computation and attracts transaction fees. Often, in practice, many transactions are small; therefore, they add computation and transmission overheads to the system. In this paper, we introduce a cost-saving approach, which significantly reduces transaction time and storage for small amount of payment, i.e. micropayment. In our approach, with the notion of ‘transaction commitment’, the computation of each transaction is much more efficient. Therefore, our approach has advantages in comparison of other cryptocurrency systems such as the bitcoin system. Our approach can be applied to other existing cryptocurrency systems.

Indra Deep Mastan, Souradyuti Paul

Mounting deanonymization attacks on the unreachable Bitcoin nodes – these nodes do not accept incoming connections – residing behind the NAT is a challenging task. Such an attack was first given by Biryukov, Khovratovich and Pustogarov based on their observation that a node can be uniquely identified in a single session by their directly-connected neighbouring nodes (ACM CCS’15). However, the BKP15 attack is less effective across multiple sessions. To address this issue, Biryukov and Pustogarov later on devised a new strategy exploiting certain properties of address-cookies (IEEE S&P’15). Unfortunately, the BP15 attack is also rendered ineffective by the present modification to the Bitcoin client.

Rémi Géraud, David Naccache, Răzvan Roşie

No abstract is available for this record.

Elli Androulaki, Christian Cachin, Angelo De, Eleftherios Kokoris-Kogias

No abstract is available for this record.

Liping Deng, Huan Chen, Jing Zeng, Liang‐Jie Zhang

No abstract is available for this record.

Juan A. Garay, Aggelos Kiayias

Consensus is arguably one of the most fundamental problems in distributed computing, playing also an important role in the area of cryptographic protocols as the enabler of a secure broadcast functionality. While the problem has a long and rich history and has been analyzed from many different perspectives, recently, with the advent of blockchain protocols like Bitcoin, it has experienced renewed interest from a much wider community of researchers and has seen its application expand to various novel settings.

Hafsa Assidi, Edoukou Berenger Ayebie, El Mamoun Souidi

No abstract is available for this record.

Christopher Carr, Anamaria Costache, Gareth T. Davies, Kristian Gjøsteen · 5 authors

No abstract is available for this record.