RippleSign: Isogeny-Based Threshold Ring Signatures with Combinatorial Methods

Threshold ring signature schemes are widely used in blockchains and cryptocurrencies. Isogeny-based signature schemes benefit from short public key and signature sizes. In this paper, by using trapdoor commitments in ring signatures, we propose a decentralized post-quantum threshold ring signature scheme, RippleSign, based on isogenies between supersingular elliptic curves. Our scheme enjoys perfect anonymity and is un-forgeable under a chosen-message attack. In terms of practicality, our threshold scheme has signature size of 187 KB with 100 participants at the 128-bit security level. In addition, our scheme takes about 2 seconds to produce (2,3)-threshold ring signature.