UC Non-Interactive, Proactive, Threshold ECDSA
Building on the Gennaro & Goldfeder and Lindell & Nof protocols (CCS ’18), we present a threshold ECDSA protocol, for any number of signatories and any threshold, that improves as follows over the state of the art: • Signature generation takes only 4 rounds (down from the current 8 rounds), with a comparable computational cost. Furthermore, 3 of these rounds can take place in a preprocessing stage before the signed message is known, lending to a non-interactive threshold ECDSA protocol. • The protocol withstands adaptive corruption of signatories. Furthermore, it includes a periodic refresh mechanism and offers full proactive security. • The protocol realizes an ideal threshold signature functionality within the UC framework, in the global random oracle model, assuming Strong RSA, semantic security of the Paillier encryption, and a somewhat enhanced variant of existential unforgeability of ECDSA. These properties (low latency, compatibility with cold-wallet architectures, proactive security, and composable security) make the protocol ideal for threshold wallets for ECDSA-based cryptocurrencies. ∗Boston University. Email: canetti@bu.edu. †Fireblocks. Emails: nikos@fireblocks.com, udi@fireblocks.com