Paper 2025/1488 Original: eprint.iacr.org/2025/1488 ↗

ABEL: Perfect Asynchronous Byzantine Extension from List-Decoding

Abstract

Asynchronous byzantine agreement extension studies the message complexity of $L$-bit multivalued asynchronous byzantine agreement given access to a binary asynchronous Byzantine agreement protocol. We prove that asynchronous byzantine agreement extension can be solved with perfect security and optimal resilience in $O(nL+n^2 \log n)$ total communication (in bits) in addition to a single call to a binary asynchronous Byzantine agreement protocol. For $L = O(n \log n)$, this gives an asymptotically optimal protocol, resolving a question that remained open for nearly two decades. List decoding is a fundamental concept in theoretical computer science and cryptography, enabling error correction beyond the unique decoding radius and playing a critical role in constructing robust codes, hardness amplification, and secure cryptographic protocols. A key novelty of our perfectly secure and optimally resilient asynchronous byzantine agreement extension protocol is that it uses list decoding - making a striking new connection between list decoding and asynchronous Byzantine agreement.