Communication-Efficient Signature-Free Asynchronous Byzantine Agreement

In this work, we focus on the problem of byzantine agreement (BA), in which
$n$
distributed processors seek to reach an agreement on an
$\ell$
-bit value, but up to
$t$
processors might be corrupted by a Byzantine adversary and act as dishonest nodes. In particular, we consider the communication-efficient BA in an asynchronous setting, where the network communication might have arbitrarily time delay. The primary challenge of designing the BA protocol in this setting is that we need to handle both the message delay from honest nodes and the Byzantine behavior from dishonest nodes simultaneously. In this work we propose a new signature-free asynchronous byzantine agreement (ABA) protocol, which achieves the optimal communication complexity of
$O(n\ell)$
when
$\ell\geq t\log t$
, given
$n\geq 5t+1$
. A protocol is said to be signature-free if the protocol design does not depend on the cryptographic machinery such as hashing and signature. To the best of our knowledge, this is the first signature-free ABA protocol that achieves the optimal communication complexity of
$O(n\ell)$
when
$\ell$
is almost linearly scaled with
$t$
.