Cryptology ePrint Archive: Report 2021/916

Mithril: Stake-based Threshold Multisignatures

Pyrros Chaidos and Aggelos Kiayias

Abstract: Stake-based multiparty cryptographic primitives operate in a setting where participants are associated with their stake, security is argued against an adversary that is bounded by the total stake it possesses —as opposed to number of parties— and we are interested in scalability, i.e., the complexity of critical operations depends only logarithmically in the number of participants (that are assumed to be numerous).

In this work we put forth a new stake-based primitive, stake-based threshold multisignatures (STM, or “Mithril” signatures), which allows the aggregation of individual signatures into a compact multisignature pro- vided the stake that supports a given message exceeds a stake threshold. This is achieved by having for each message a pseudorandomly sampled subset of participants eligible to issue an individual signature; this ensures the scalability of signing, aggregation and verification.

We formalize the primitive in the universal composition setting and propose efficient constructions for STMs. We also showcase that STMs are eminently useful in the cryptocurrency setting by providing two applications: (i) stakeholder decision-making for Proof of Work (PoW) blockchains, specifically, Bitcoin, and (ii) fast bootstrapping for Proof of Stake (PoS) blockchains.

Category / Keywords: cryptographic protocols / digital signatures, zero knowledge, blockchains

Date: received 6 Jul 2021, last revised 23 Sep 2021

Contact author: pchaidos at di uoa gr, akiayias at inf ed ac uk

Available format(s): PDF | BibTeX Citation

Note: Notation improvements, added explicit initialization/operation separation via prepending AVK to msg.

Version: 20210923:063855 (All versions of this report)

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