Paper 2022/550

ROAST: Robust Asynchronous Schnorr Threshold Signatures

Tim Ruffing, Viktoria Ronge, Elliott Jin, Jonas Schneider-Bensch, and Dominique Schröder

Abstract

Bitcoin and other cryptocurrencies have recently introduced support for Schnorr signatures whose cleaner algebraic structure, as compared to ECDSA, allows for simpler and more practical constructions of highly demanded "$t$-of-$n$" threshold signatures. However, existing Schnorr threshold signature schemes (like their ECDSA counterparts) still fall short of the needs of real-world applications due to their assumption that the network is synchronous and due to their lack of robustness, i.e., the guarantee that $t$ honest signers are able to obtain a valid signature even in the presence of other malicious signers who try to disrupt the protocol. This hinders the adoption of threshold signatures in the cryptocurrency ecosystem, e.g., in second-layer protocols built on top of cryptocurrencies. In this work, we propose $\mathsf{ROAST}$, a simple wrapper that turns a given threshold signature scheme into a scheme with a robust and asynchronous signing protocol, as long as the underlying signing protocol is semi-interactive (i.e., has one preprocessing round and one actual signing round), provides identifiable aborts, and is unforgeable under concurrent signing sessions. When applied to the state-of-the-art Schnorr threshold signature scheme $\mathsf{FROST}$, which fulfills these requirements, we obtain a simple, efficient, and highly practical Schnorr threshold signature scheme.

Metadata
Available format(s)
PDF
Category
Cryptographic protocols
Publication info
Preprint. Minor revision.
Keywords
threshold cryptographythreshold signaturesSchnorr signaturesrobustness
Contact author(s)
crypto @ timruffing de
History
2022-05-10: received
Short URL
https://ia.cr/2022/550
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2022/550,
      author = {Tim Ruffing and Viktoria Ronge and Elliott Jin and Jonas Schneider-Bensch and Dominique Schröder},
      title = {ROAST: Robust Asynchronous Schnorr Threshold Signatures},
      howpublished = {Cryptology ePrint Archive, Paper 2022/550},
      year = {2022},
      note = {\url{https://eprint.iacr.org/2022/550}},
      url = {https://eprint.iacr.org/2022/550}
}
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