Abstract
We study the problem of atomic broadcast—the underlying problem addressed by blockchain protocols—in the presence of a malicious adversary who corrupts some fraction of the n parties running the protocol. Existing protocols are either robust for any number of corruptions in a synchronous network (where messages are delivered within some known time \(\varDelta \)) but fail if the synchrony assumption is violated, or tolerate fewer than n/3 corrupted parties in an asynchronous network (where messages can be delayed arbitrarily) and cannot tolerate more corruptions even if the network happens to be well behaved.
We design an atomic broadcast protocol (Tardigrade) that, for any \(t_s \ge t_a\) with \(2t_s + t_a < n\), provides security against \(t_s\) corrupted parties if the network is synchronous, while remaining secure when \(t_a\) parties are corrupted even in an asynchronous network. We show that Tardigrade achieves optimal tradeoffs between \(t_s\) and \(t_a\). Finally, we show a second protocol (upgrade) with similar (but slightly weaker) guarantees that achieves per-transaction communication complexity linear in n.
J. Katz—Work performed under financial assistance award 70NANB19H126 from the U.S. Department of Commerce, National Institute of Standards and Technology, and also supported in part by NSF award #1837517.
J. Loss—Portions of this work were done while at University of Maryland and Ruhr University Bochum.
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Notes
- 1.
Tardigrades, also called water bears, are microscopic animals known for their ability to survive in extreme environments.
- 2.
This does not contradict the existence of synchronous ABC protocols for \(t_s < n\), since such protocols are insecure in an asynchronous setting even if no parties are corrupted.
- 3.
Available at: eprint.iacr.org/2020/142.pdf.
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Blum, E., Katz, J., Loss, J. (2021). Tardigrade: An Atomic Broadcast Protocol for Arbitrary Network Conditions. In: Tibouchi, M., Wang, H. (eds) Advances in Cryptology – ASIACRYPT 2021. ASIACRYPT 2021. Lecture Notes in Computer Science(), vol 13091. Springer, Cham. https://doi.org/10.1007/978-3-030-92075-3_19
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