arXiv subjects

Alin Tomescu

Publications and source records attributed to Alin Tomescu.

3 recordsLinked to original sources

arXiv2021

Reaching Consensus for Asynchronous Distributed Key Generation

We give a protocol for Asynchronous Distributed Key Generation (A-DKG) that is optimally resilient (can withstand $f<\frac{n}{3}$ faulty parties), has a constant expected number of rounds, has $\tilde{O}(n^3)$ expected communication complexity, and assumes only the existence of a PKI. Prior to our work, the best A-DKG protocols required $Ω(n)$ expected number of rounds, and $Ω(n^4)$ expected communication. Our A-DKG protocol relies on several building blocks that are of independent interest. We define and design a Proposal Election (PE) protocol that allows parties to retrospectively agree on a valid proposal after enough proposals have been sent from different parties. With constant probability the elected proposal was proposed by a non-faulty party. In building our PE protocol, we design a Verifiable Gather protocol which allows parties to communicate which proposals they have and have not seen in a verifiable manner. The final building block to our A-DKG is a Validated Asynchronous Byzantine Agreement (VABA) protocol. We use our PE protocol to construct a VABA protocol that does not require leaders or an asynchronous DKG setup. Our VABA protocol can be used more generally when it is not possible to use threshold signatures.

cs.DC↗

arXiv2019

SBFT: a Scalable and Decentralized Trust Infrastructure

SBFT is a state of the art Byzantine fault tolerant permissioned blockchain system that addresses the challenges of scalability, decentralization and world-scale geo-replication. SBFTis optimized for decentralization and can easily handle more than 200 active replicas in a real world-scale deployment. We evaluate \sysname in a world-scale geo-replicated deployment with 209 replicas withstanding f=64 Byzantine failures. We provide experiments that show how the different algorithmic ingredients of \sysname increase its performance and scalability. The results show that SBFT simultaneously provides almost 2x better throughput and about 1.5x better latency relative to a highly optimized system that implements the PBFT protocol. To achieve this performance improvement, SBFT uses a combination of four ingredients: using collectors and threshold signatures to reduce communication to linear, using an optimistic fast path, reducing client communication and utilizing redundant servers for the fast path.

cs.DC↗

arXiv2018

sAVSS: Scalable Asynchronous Verifiable Secret Sharing in BFT Protocols

This paper introduces a new way to incorporate verifiable secret sharing (VSS) schemes into Byzantine Fault Tolerance (BFT) protocols. This technique extends the threshold guarantee of classical Byzantine Fault Tolerant algorithms to include privacy as well. This provides applications with a powerful primitive: a threshold trusted third party, which simplifies many difficult problems such as a fair exchange. In order to incorporate VSS into BFT, we introduced sAVSS, a framework that transforms any VSS scheme into an asynchronous VSS scheme with constant overhead. By incorporating Kate et al.'s scheme into our framework, we obtain an asynchronous VSS that has constant overhead on each replica -- the first of its kind. We show that a key-value store built using BFT replication and sAVSS supports writing secret-shared values with about a 30% - 50% throughput overhead with less than 35 millisecond request latencies.

cs.CR↗