Research Pulse Issue #8 04/09/2021

  1. Decentralized and Lightweight Approach to Detect Eclipse Attacks on Proof of Work Blockchains [Paywalled]
    Authors: Bithin Alangot, Daniel Reijsbergen, Sarad Venugopalan, Pawel Szalachowski, and Kiat Seng Yeo

Clients of permissionless blockchain systems, like Bitcoin, rely on an underlying peer-to-peer network to send and receive transactions. It is critical that a client is connected to at least one honest peer, as otherwise the client can be convinced to accept a maliciously forked view of the blockchain. In such an eclipse attack, the client is unable to reliably distinguish the canonical view of the blockchain from the view provided by the attacker. The consequences of this can be catastrophic if the client makes business decisions based on a distorted view of the blockchain transactions. In this paper, we investigate the design space and propose two approaches for Bitcoin clients to detect whether an eclipse attack against them is ongoing. Each approach chooses a different trade-off between average attack detection time and network load. The first scheme is based on the detection of suspicious block timestamps. The second scheme allows blockchain clients to utilize their natural connections to the Internet (i.e., standard web activity) to gossip about their blockchain views with contacted servers and their other clients. Our proposals improve upon previously proposed eclipse attack countermeasures without introducing any dedicated infrastructure or changes to the Bitcoin protocol and network, and we discuss an implementation. We demonstrate the effectiveness of the gossip-based schemes through rigorous analysis using original Internet traffic traces and real-world deployment. The results indicate that our protocol incurs a negligible overhead and detects eclipse attacks rapidly with high probability, and is well-suited for practical deployment.

Link: Decentralized and Lightweight Approach to Detect Eclipse Attacks on Proof of Work Blockchains | IEEE Journals & Magazine | IEEE Xplore

  1. Federated Learning Meets Blockchain in Edge Computing: Opportunities and Challenges
    Authors: Dinh C. Nguyen, Ming Ding, Quoc-Viet Pham, Pubudu N. Pathirana, Long Bao Le, Aruna Seneviratne, Jun Li, Dusit Niyato, and H. Vincent Poor

Mobile edge computing (MEC) has been envisioned as a promising paradigm to handle the massive volume of data generated from ubiquitous mobile devices for enabling intelligent services with the help of artificial intelligence (AI). Traditionally, AI techniques often require centralized data collection and training in a single entity, e.g., an MEC server, which is now becoming a weak point due to data privacy concerns and high data communication overheads. In this context, federated learning (FL) has been proposed to provide collaborative data training solutions, by coordinating multiple mobile devices to train a shared AI model without exposing their data, which enjoys considerable privacy enhancement. To improve the security and scalability of FL implementation, blockchain as a ledger technology is attractive for realizing decentralized FL training without the need for any central server. Particularly, the integration of FL and blockchain leads to a new paradigm, called FLchain, which potentially transforms intelligent MEC networks into decentralized, secure, and privacy-enhancing systems. This article presents an overview of the fundamental concepts and explores the opportunities of FLchain in MEC networks. We identify several main topics in FLchain design, including communication cost, resource allocation, incentive mechanism, security and privacy protection. The key solutions for FLchain design are provided, and the lessons learned as well as the outlooks are also discussed. Then, we investigate the applications of FLchain in popular MEC domains, such as edge data sharing, edge content caching and edge crowdsensing. Finally, important research challenges and future directions are also highlighted.


  1. DOC-BLOCK: A Blockchain Based Authentication System for Digital Documents [Paywalled]
    Authors: Iftekher Toufique Imam, Yamin Arafat, Kazi Saeed Alam, and Shaikh Aki

With the rapid growth in the sector of information technology and easy access to cheap and advanced office instruments in the market, the faking of important documents has become a matter of concern nowadays. Therefore, the need for verification and authentication practices of various important documents in the form of banking documents, government documents, transaction documents, educational certificates etc is also increasing. However, various challenging and tedious processes have made document verification very complex and time-consuming which motivated us to conduct this research. In this paper, we present a decentralized web application for digital document verification using Ethereum blockchain-based technology in P2P cloud storage to enhance the verification process by making it more open, transparent, and auditable. The proposed model includes several methods such as public/private key cryptography, online storage security, digital signatures, hash, peer-to-peer networks and proof of work which has made the verification of any uploaded documents for any organization or authority faster and convenient with just a click. Furthermore, respective hash values are also assigned to each individual document. Our proposed model successfully meets up all the criteria for a digital document verification system by alleviating the gaps and difficulties in the traditional methods in document verification.

Link: DOC-BLOCK: A Blockchain Based Authentication System for Digital Documents | IEEE Conference Publication | IEEE Xplore

  1. Pooling is not Favorable: Decentralize Mining Power of PoW Blockchain Using Age-of-Work
    Authors: Long Shi, Taotao Wang, Jun Li, and Shengli Zhang

As the underlying consensus protocol of Bitcoin and Ethereum blockchain, Proof-of-Work (PoW) features a cryptographic mathematical puzzle whose solution is easy to verify but extremely hard to solve. Under PoW, miners maintain the security of blockchain by devoting computing powers to solve the puzzle; the miner who has solved the puzzle successfully generates a block, along with a reward (e.g., a set of cryptocurrency). The average waiting time to generate a block is inversely proportional to the computing power of the miner. To reduce the average block generation time, a group of individual miners can form a mining pool to aggregate their computing power to solve the puzzle together and share the reward contained in the block. However, if the aggregated computing power of the pool forms a substantial portion of the total computing power in the network, the pooled mining undermines the core spirit of blockchain, i.e., the decentralization, and harms its security. To discourage the pooled mining, we develop a new consensus protocol called Proofof-Age (PoA) that builds upon the native PoW protocol. The core idea of PoA lies in using Age-of-Work (AoW) to measure the effective mining period that the miner has devoted to maintaining the security of blockchain. Unlike in the native PoW protocol, in our PoA protocol, miners benefit from its effective mining period even if they have not successfully mined a block. We first employ a continuous time Markov chain (CTMC) to model the block generation process of the PoA based blockchain. Based on thi s CTMC model, we then analyze the block generation rates of the mining pool and solo miner respectively. Our analytical results verify that under PoA, the block generation rates of miners i n the mining pool are reduced compared to that of solo miners, thereby disincentivizing the pooled mining. Finally, we simulate the mining process in the PoA blockchain to demonstrate the consistency of the analytical results.


  1. A Coercion-Resistant Blockchain-Based E-Voting Protocol with Receipts
    Authors: Chiara Spadafora, Riccardo Longo, and Massimiliano Sala

We propose a decentralized e-voting protocol that is coercion-resistant and vote-selling resistant, while being also completely transparent and not receipt-free. We achieve decentralization using blockchain technology. Because of the properties such as transparency, decentralization, and non-repudiation, blockchain is a fundamental technology of great interest in its own right, and it also has large potential when integrated into many other areas. We prove the security of the protocol under the standard DDH assumption on the underlying prime-order cyclic group (e.g. the group of points of an elliptic curve), as well as under standard assumptions on blockchain robustness.


  1. A Formal Analysis of the MimbleWimble Cryptocurrency Protocol
    Authors: Adrián Silveira, Gustavo Betarte, Maximiliano Cristiá, and Carlos Luna

MimbleWimble (MW) is a privacy-oriented cryptocurrency technology which provides security and scalability properties that distinguish it from other protocols of its kind. We present and discuss those properties and outline the basis of a model-driven verification approach to address the certification of the correctness of the protocol implementations. In particular, we propose an idealized model that is key in the described verification process, and identify and precisely state sufficient conditions for our model to ensure the verification of relevant security properties of MW. Since MW is built on top of a consensus protocol, we develop a Z specification of one such protocol and present an excerpt of the {log } prototype generated from the Z specification. This {log } prototype can be used as an executable model where simulations can be run. This allows us to analyze the behavior of the protocol without having to implement it in a low level programming language. Finally, we analyze the Grin and Beam implementations of MW in their current state of development.


  1. Design and Implementation of Blockchain-based E-Voting
    Authors: Moritz Eck, Alex Scheitlin, and Nik Zaugg

Voting is an essential part of modern democracies. Thus, changes to the processes are always delicate and highly debated. A prime example of this is the introduction of remote electronic voting (E-Voting) which can be deployed as a supplement or even replacement for traditional ballot-box or postal voting. There exist high requirements for such systems to satisfy the vote’s privacy and the process’ verifiability. In recent years, a lot of research has been conducted on how to apply cryptographic techniques to meet these requirements. Some countries have even already tested or are using centralized E-voting systems. The recent developments in the blockchain area provide suitable solutions to decentralize such systems. Built on established cryptographic techniques, this work proposes a secure and verifiable design for a distributed E-voting system. The encryption and decryption keys are generated in a distributed manner by multiple cooperating parties. The encryption of the vote and the proof for the vote’s validity are generated on the voter’s device. Finally, the encrypted votes are publicly stored and verified on the decentralized public ledger (i.e., the blockchain). The proposed design is implemented in a proof-of-concept E-Voting system based on a blockchain. The system is verifiable and the voter’s privacy is ensured through cryptographic primitives. Additionally, limitations and future applications of blockchains in the context of E-Voting are highlighted.


  1. Security of the Poseidon Hash Function Against Non-Binary Differential and Linear Attacks [Paywalled]
    Authors: L. Kovalchuk, R. Oliynykov, and M. Rodinko

In the paper, we construct security estimations of Poseidon hash function against non-binary linear and differential attacks. We adduce the general parameters for the Poseidon hash function that allow using this hash function in recurrent SNARK-proofs based on MNT-4 and MNT-6 triplets. We also analyse how to choose S-boxes for such function for this choice to be optimal from the point of view of the number of constraints and security. We show how many full rounds are sufficient to guarantee security of such hash function against non-binary linear and differential attacks. We also calculate the number of constraints per bit achieved in the proposed realizations and demonstrate a considerable gain as compared to the Pedersen hash function.


  1. State-Dependent Processing in Payment Channel Networks for Throughput Optimization
    Authors: Nikolaos Papadis and Leandros Tassiulas

Payment channel networks (PCNs) have emerged as a scalability solution for blockchains built on the concept of a payment channel: a setting that allows two nodes to safely transact between themselves in high frequencies based on pre-committed peer-to-peer balances. Transaction requests in these networks may be declined because of unavailability of funds due to temporary uneven distribution of the channel balances. In this paper, we investigate how to alleviate unnecessary payment blockage via proper prioritization of the transaction execution order. Specifically, we consider the scheduling problem in PCNs: as transactions continuously arrive on both sides of a channel, nodes need to decide which ones to process and when in order to maximize their objective, which in our case is the channel throughput. We introduce a stochastic model to capture the dynamics of a payment channel under random arrivals, and propose that channels can hold incoming transactions in buffers up to some deadline in order to enable more elaborate processing decisions. We describe a policy that maximizes the channel success rate/throughput for uniform transaction requests of fixed amounts, both in the presence and absence of buffering capabilities, and formally prove its optimality. We also develop a discrete event simulator of a payment channel, and evaluate different heuristic scheduling policies in the more general heterogeneous amounts case, with the results showing superiority of the heuristic extension of our policy in this case as well. Our work opens the way for more formal research on improving PCN performance via joint consideration of routing and scheduling decisions.


  1. Analysis and Probing of Parallel Channels in the Lightning Network
    Authors: Alex Biryukov, Gleb Naumenko, and Sergei Tikhomirov

The Lightning Network (LN) is a prominent scalability solution for Bitcoin that allows for low-latency off-chain payments through a network of payment channels. LN users lock bitcoins into collaboratively owned addresses and redistribute the ownership of these funds without confirming each transfer on-chain. The LN introduces new privacy challenges. In this paper, we focus on channel balance probing. We propose a new model of the LN that accounts for parallel and unidirectional channels, which has not been done in prior work. We describe a probing algorithm that accurately updates the attacker’s balance estimates without the need to directly connect to victims. We introduce an uncertainty-based metric to measure the attacker’s information gain. We implement the first probing-focused LN simulator and suggest several countermeasures against general probing (implemented considering parallel channels). We evaluate these techniques using the simulator, as well as experiments on the real network. According to our simulations, an attacker can infer up to 80% information regarding channel balances spending ≈ 20 seconds per channel. The suggested countermeasures limit the attacker’s gain at 30%, while also increasing the attack time by 2-4x. In addition, we describe sophisticated attack techniques that combine fee-probing and channel jamming to get precise access to individual channel balances inside a hop, and test them against the real network. Finally, we discuss payment flows and their concealment.


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A noticeable uptick this week in papers targeting blockchain-powered E-voting schemes. Whether that is a reflection of current geopolitical tensions or not, it is interesting to see new schemes as described in Design and Implementation of Blockchain-based E-Voting approaching the cryptographic challenge of building e-voting systems that simultaneously provide privacy, transparency and tamper proofs.

Also of note was the release of Security of the Poseidon Hash Function Against Non-Binary Differential and Linear Attacks, one of the first in-depth analysis of the security of Poseidon, an emerging cryptographic hash function designed to optimize performance when used in Zero Knowledge Proof schemes.

Finally, Analysis and Probing of Parallel Channels in the Lightning Network provides a novel approach to network analysis in the Lightning Network and highlights potential attacks that deanonymize users. This will probably be my weekend read!

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I am particularly interested in where this is going.