OciorABA: Improved Error-Free Asynchronous Byzantine Agreement via Partial Vector Agreement

Abstract: In this work, we propose an error-free, information-theoretically secure multi-valued asynchronous Byzantine agreement (ABA) protocol, called OciorABA. This protocol achieves ABA consensus on an $\ell$-bit message with an expected communication complexity of $O(n\ell + n^3 \log q )$ bits and an expected round complexity of $O(1)$ rounds, under the optimal resilience condition $n \geq 3t + 1$ in an $n$-node network, where up to $t$ nodes may be dishonest. Here, $q$ denotes the alphabet size of the error correction code used in the protocol. In our protocol design, we introduce a new primitive: asynchronous partial vector agreement (APVA). In APVA, the distributed nodes input their vectors and aim to output a common vector, where some of the elements of those vectors may be missing or unknown. We propose an APVA protocol with an expected communication complexity of $O( n^3 \log q )$ bits and an expected round complexity of $O(1)$ rounds. This APVA protocol serves as a key building block for our OciorABA protocol.