The Blockchain Day will be held at Bar-Ilan University, Wed, Apr 19th, 2023 at the Faculty of Engineering, Building 1102, room 22 (on the ground floor).
The Blockchain Day is organized as part of the MEGA-ACE center, supported by the Algorand Foundation through the Algorand-Centers-of-Excellence (ACE) Program.
Organizers: Ran Cohen (Reichman University) and Carmit Hazay (Bar-Ilan University)
10:00-11:00 Rafael Pass, Simplex Consensus: A Simple and Fast Consensus Protocol (slides)
11:00-11:30 Coffee break
11:30-12:30 Ittay Eyal, Authentication (slides)
14:00-15:00 Vassilis Zikas, A Rational Protocol Treatment of 51% Attacks
15:00-15:30 Coffee break
15:30-16:30 Tal Moran, Self-Healing Consensus from Rate-Limiting Resources
Simplex Consensus: A Simple and Fast Consensus Protocol
Rafael Pass, Tel Aviv University and Cornell Tech
We present a theoretical framework for analyzing the efficiency of consensus protocols, and apply it to analyze the optimistic and pessimistic confirmation times of state-of-the-art partially-synchronous protocols in the so-called "rotating leader/random leader" model of consensus (recently popularized in the blockchain setting). We next present a new and simple consensus protocol in the partially synchronous setting, tolerating byzantine faults; in our eyes, this protocol is essentially as simple to describe as the simplest known protocols, but it also enjoys an even simpler security proof, while matching and, even improving, the efficiency of the state-of-the-art (according to our theoretical framework).
As with the state-of-the-art protocols, our protocol assumes a (bare) PKI, a digital signature scheme, collision-resistant hash functions, and a random leader election oracle, which may be instantiated with a random oracle (or a CRS).
Joint work with Benjamin Chan
Ittay Eyal, Technion
Authentication is the first, crucial step in securing digital assets like cryptocurrencies and decentralized identities (as well as online services like banking and social networks). It relies on users maintaining exclusive access to credentials like cryptographic signing keys, passwords, and physical devices. Authentication mechanisms try to identify users despite credential loss, leakage, or theft. In practice, mechanism failures result in the loss of assets and identity theft. Nevertheless, the design of authentication mechanisms remained an open theoretical question, solved heuristically by practitioners.
We formalize the classical authentication problem. This formalization almost immediately reveals surprising results. We present bounds and maximal authentication mechanisms for different variations of the problem. Our results have immediate practical implications for cryptocurrency client security.
A Rational Protocol Treatment of 51% Attacks
Vassilis Zikas, Purdue University
Game-theoretic analyses of cryptocurrencies and---more generally---blockchain-based decentralized ledgers offer insight on their economic robustness and behavior when even their underpinning cryptographic assumptions fail. In this work we utilize the recently proposed blockchain adaptation of the rational protocol design (RPD) framework [EUROCRYPT'18] to analyze 51% double-spending attacks against Nakamoto-style proof-of-work based cryptocurrencies. We first observe a property of the originally proposed utility class that yields an unnatural conclusion against such attacks, and show how to devise a utility that avoids this pitfall and makes predictions that match the observable behavior---i.e., that renders attacking a dominant strategy in settings where an attack was indeed observed in reality. We then propose a generic remedy to the underlying protocol parameters that provably deter adversaries controlling a majority of the system's resources from attacks on blockchain consistency, including the 51% double-spending attack. This can be used as guidance to patch systems that have suffered such attacks, e.g., Ethereum Classic and Bitcoin Cash, and serves as a demonstration of the power of game-theoretic analyses.
Self-Healing Consensus From Rate-Limiting Resources
Tal Moran, Reichman University
The "claim to fame" of Nakamoto consensus is being permissionless. However, it also has another novel, but less studied, property: it can self-heal from arbtirary violations of its underlying communication and honest-majority assumptions. Even if an adversary completely controls the network and corrupts all parties for a limited period of time, the protocol will guarantee consensus after the network and honest majority are restored. The self-healing of Nakamoto consensus strongly relies on the specific properties of its random-oracle-based proofs of work. Indeed, while permissionless consensus protocols have been constructed from alternative resource proofs, they either sacrifice self-healing, or also rely on specific non-standard assumptions that make them "behave like" RO-based PoWs.
We show that self-healing consensus can be based on generic resource proofs, with much weaker requirements. Along the way, we develop formal frameworks for defining self-healing in general distributed protocols and for defining Rate-Limiting Resource Proofs (RLRPs) that capture sufficient requirements for achieve self-healing consensus, but can be realized with a much larger class of resource proofs (including "useful" work, spacetime, and even stake).