Paper 2020/958

Multi-Threshold Asynchronous Reliable Broadcast and Consensus

Martin Hirt, Ard Kastrati, and Chen-Da Liu-Zhang


Classical protocols for reliable broadcast and consensus provide security guarantees as long as the number of corrupted parties $f$ is bounded by a single given threshold $t$. If $f > t$, these protocols are completely deemed insecure. We consider the relaxed notion of multi-threshold reliable broadcast and consensus where validity, consistency and termination are guaranteed as long as $f \le t_v$, $f \le t_c$ and $f \le t_t$ respectively. For consensus, we consider both variants of $(1-\epsilon)$-consensus and \emph{almost-surely terminating} consensus, where termination is guaranteed with probability $(1-\epsilon)$ and $1$, respectively. We give a very complete characterization for these primitives in the asynchronous setting and with no signatures: -Multi-threshold reliable broadcast is possible if and only if $\max\{t_c,t_v\} + 2t_t < n$. -Multi-threshold almost-surely consensus is possible if $\max\{t_c, t_v\} + 2t_t < n$, $2t_v + t_t < n$ and $t_t < n/3$. Assuming a global coin, it is possible if and only if $\max\{t_c, t_v\} + 2t_t < n$ and $2t_v + t_t < n$. -Multi-threshold $(1-\epsilon)$-consensus is possible if and only if $\max\{t_c, t_v\} + 2t_t < n$ and $2t_v + t_t < n$.

Available format(s)
Cryptographic protocols
Publication info
Preprint. MINOR revision.
reliable broadcastconsensusbyzantine agreementmulti-threshold
Contact author(s)
lichen @ inf ethz ch
2020-08-11: received
Short URL
Creative Commons Attribution


      author = {Martin Hirt and Ard Kastrati and Chen-Da Liu-Zhang},
      title = {Multi-Threshold Asynchronous Reliable Broadcast and Consensus},
      howpublished = {Cryptology ePrint Archive, Paper 2020/958},
      year = {2020},
      note = {\url{}},
      url = {}
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