Expand description
Implementation of threshold BBS and BBS+ based on the paper Threshold BBS+ Signatures for Distributed Anonymous Credential Issuance The threshold signing protocol has 3 phases (not communication rounds) 1. This is the randomness generation phase 2. This is the phase where multiplications happen 3. Here the outputs of phases 1 and 2 and the messages to be signed are used to generate the signature. This phase is non-interactive from signers’ point of view as they don’t just interact among themselves
Note that only 3rd phase requires the messages to be known so the first 2 phases can be treated as pre-computation
and can be done proactively and thus only phase 1 and 2 are online phases of the MPC protocol and phase 3 is the offline
phase.
Secondly since the communication time among signers is most likely to be the bottleneck
in threshold signing, phase 1 and 2 support batching meaning that to generate n signatures only a single execution
of phase 1 and 2 needs to done, although with larger inputs. Then n executions of phase 3 are done to generate
the signature.
Also, its assumed that parties have done the DKG as well as the base OT and stored their results before starting phase 1.
Both BBS and BBS+ implementations share the same multiplication phase and the base OT phase but their phase 1 is slightly
less expensive as BBS+ needs 2 random fields elements but BBS needs only 1.
Modules§
- multiplication_
phase - The multiplication phase of the threshold signing protocol of BBS and BBS+.
- randomness_
generation_ phase - threshold_
bbs - threshold_
bbs_ plus - utils