IPFS and Friends: A Qualitative Comparison of Next Generation Peer-to-Peer Data Networks
Authors: Erik Daniel and Florian Tschorsch
Decentralized, distributed storage offers a way to reduce the impact of data silos as often fostered by centralized cloud storage. While the intentions of this trend are not new, the topic gained traction due to technological advancements, most notably blockchain networks. As a consequence, we observe that a new generation of peer-to-peer data networks emerges. In this survey paper, we therefore provide a technical overview of the next generation data networks. We use select data networks to introduce general concepts and to emphasize new developments. We identify common building blocks and provide a qualitative comparison. From the overview, we derive future challenges and research goals concerning data networks.
Formal Analysis of Composable DeFi Protocols
Authors: Palina Tolmach, Yi Li, Shang-Wei Lin, and Yang Liu
Decentralized finance (DeFi) has become one of the most successful applications of blockchain and smart contracts. The DeFi ecosystem enables a wide range of crypto-financial activities, while the underlying smart contracts often contain bugs, with many vulnerabilities arising from the unforeseen consequences of composing DeFi protocols together. In this paper, we propose a formal process-algebraic technique that models DeFi protocols in a compositional manner to allow for efficient property verification. We also conduct a case study to demonstrate the proposed approach in analyzing the composition of two interacting DeFi protocols, namely, Curve and Compound. Finally, we discuss how the proposed modeling and verification approach can be used to analyze financial and security properties of interest.
The Nym Network
The Next Generation of Privacy Infrastructure
Authors: Claudia Diaz, Harry Halpin, and Aggelos Kiayias
The Nym network (“Nym”) is a decentralized and incentivized infrastructure to provision privacy to a broad range of message-based applications and services. The core component of Nym is a mixnet that protects network traffic metadata for applications, providing communication privacy superior to both VPNs and Tor against global adversaries that can watch the entire internet. Nodes in the mixnet are rewarded via a novel proof of mixing scheme that proves that mix nodes are providing a high quality of service. Rewards given by NYM tokens allow anyone to join the Nym network and enable a sustainable economic model for privacy. NYM tokens can be transformed into anonymous credentials that allow users to privately prove their “right to use” services in a decentralized and verifiable manner. The Nym network can serve as the foundation for a vast range of privacy-enhanced applications that defend the fundamental freedoms of people across the globe against traffic analysis by powerful adversaries.
WabiSabi: Centrally Coordinated CoinJoins with Variable Amounts
Authors: Ádám Ficsór, Yuval Kogman, Lucas Ontivero, and István András Seres
Bitcoin transfers value on a public ledger of transactions anyone can verify. Coin ownership is defined in terms of public keys. Despite potential use for private transfers, research has shown that users’ activity can often be traced in practice. Businesses have been built on dragnet surveillance of Bitcoin users because of this lack of strong privacy, which harms its fungibility, a basic property of functional money. Although the public nature of this design lacks strong guarantees for privacy, it does not rule it out. A number of methods have been proposed to strengthen privacy. Among these is CoinJoin, an approach based on multiparty transactions that can introduce ambiguity and break common assumptions that underlie heuristics used for deanonymization. Existing implementations of CoinJoin have several limitations which may partly explain the lack of their widespread adoption. This work introduces WabiSabi, a new protocol for centrally coordinated CoinJoin implementations utilizing keyed verification anonymous credentials and homomorphic value commitments. This improves earlier approaches which utilize blind signatures in both privacy and flexibility, enabling novel use cases and reduced overhead.
YOSO: You Only Speak Once. Secure MPC with Stateless Ephemeral Roles
Authors: Craig Gentry, Shai Halevi, Hugo Krawczyk, Bernardo Magri, Jesper Buus Nielsen, Tal Rabin, and Sophia Yakoubov
The inherent difficulty of maintaining stateful environments over long periods of time gave rise to the paradigm of serverless computing, where mostly-stateless components are deployed on demand to handle computation tasks, and are teared down once their task is complete. Serverless architecture could offer the added benefit of improved resistance to targeted denial-of-service attacks, by hiding from the attacker the physical machines involved in the protocol until after they complete their work. Realizing such protection, however, requires that the protocol only uses stateless parties, where each party sends only one message and never needs to speaks again. Perhaps the most famous example of this style of protocols is the Nakamoto consensus protocol used in Bitcoin: A peer can win the right to produce the next block by running a local lottery (mining), all while staying covert. Once the right has been won, it is executed by sending a single message. After that, the physical entity never needs to send more messages. We refer to this as the You-Only-Speak-Once (YOSO) property, and initiate the formal study of it within a new model that we call the YOSO model. Our model is centered around the notion of roles, which are stateless parties that can only send a single message. Crucially, our modelling separates the protocol design, that only uses roles, from the role-assignment mechanism, that assigns roles to actual physical entities. This separation enables studying these two aspects separately, and our YOSO model in this work only deals with the protocol-design aspect. We describe several techniques for achieving YOSO MPC; both computational and information theoretic. Our protocols are synchronous and provide guaranteed output delivery (which is important for application domains such as blockchains), assuming honest majority of roles in every time step. We describe a practically efficient computationally-secure protocol, as well as a proof-of-concept information theoretically secure protocol.
Improved Certificate Creation and Verification Architecture Using Hybrid
Authors: Muhammad Anwarul Azim and Md. Jawwad Bin Zahir
Certificates containing proof of certain aspects of an entity are mostly given as printed papers by government institutes and their supporting organizations in some countries. The verification of these certificates is rather time-consuming. Also, a common platform to create and verify certificates securely and transparently is somehow missing. These allow offenders to forge certificates as well as tamper containing information. To address these problems of the certificate management system, a blockchain-based certificate management system is proposed in this paper. In addition to a database to reuse information about certificate owners, the system consists of two major modules. The creation module takes properly validated and authorized information and stores them into the blockchain along with its hash value to provide E-Certificates. Using hash values, the verification module verifies both paper certificates and E-Certificates. The system prevents attempts to create fake certificates or tamper with them. Hashing enhances the security of the system and, tamper-resistant immutable records ensure transparency. By utilizing index servers, the system reduces operational cost and verification time as well as enables large-scale use of the system.
An Overview of Cryptographic Accumulators
Authors: Ilker Ozcelik, Sai Medury, Justin Broaddus, and Anthony Skjellum
This paper contributes a primer on cryptographic accumulators and how to apply them practically. A cryptographic accumulator is a space- and time-efficient data structure used for set membership tests. Since it is possible to represent any computational problem where the answer is yes or no as a set-membership problem, cryptographic accumulators are invaluable data structures in computer science and engineering. But, to the best of our knowledge, there is neither a concise survey comparing and contrasting various types of accumulators nor a guide for how to apply the most appropriate one for a given application. Therefore, we address that gap by describing cryptographic accumulators while presenting their fundamental and so-called optional properties. We discuss the effects of each property on the given accumulator’s performance in terms of space and time complexity, as well as communication overhead.
Smart Contracts for Incentivized Outsourcing of Computation
Authors: Alptekin Kupcu and Reihaneh Safavi-Naini
Outsourcing computation allows resource limited clients to access computing on demand. Various types of clusters, grids, and clouds, such as Microsoft’s Azure and Amazon’s EC2, form today’s outsourced computing infrastructure. A basic requirement of outsourcing is providing guarantee that the computation result is correct. We consider an automated and efficient way of achieving assurance where the computation is replicated and outsourced to two contractors by a smart contract that will decide on the correctness of the computation result, by comparing the two received results. We show that all previous incentivized outsourcing protocols with proven correctness fail when automated by a smart contract, because of copy attack where a contractor simply copies the submitted response of the other contractor. We then design an incentive mechanism that uses two lightweight response-checking protocols, and employ monetary reward, fine, and bounty to incentivize correct computation. We use game theory to model and analyze our mechanism, and prove that it has a single Nash equilibrium, corresponding to the contractors’ strategy of correctly computing the result. Our work provides a foundation for incentivized computation in the smart contract setting and opens new research directions.
Authors: Markulf Kohlweiss, Mary Maller, Janno Siim, and Mikhail Volkhov
Succinct non-interactive arguments of knowledge (SNARKs) have found numerous applications in the blockchain setting and elsewhere. The most efficient SNARKs require a distributed ceremony protocol to generate public parameters, also known as a structured reference string (SRS). Our contributions are two-fold:
– We give a security framework for non-interactive zero-knowledge arguments with a ceremony protocol.
– We revisit the ceremony protocol of Groth’s SNARK [Bowe et al., 2017]. We show that the original construction can be simplified and optimized, and then prove its security in our new framework. Importantly, our construction avoids the random beacon model used in the original work.