FROST Round Two: Signature Share Generation #8
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computeChallenge implements def compute_group_commitment(commitment_list, binding_factor_list) from [FROST] as defined in section 4.6. Signature Challenge Computation.
This way we iterate only once over the commitments. The participant list will be needed in Round2 function of signer.
Round2 implements the Round Two - Signature Share Generation phase from [FROST], section 5.2 Round Two - Signature Share Generation. This code is not yet covered with unit tests and until this happens should be treated as a late prototype.
The validateGroupCommitments logic was improved to cover the case when the commitment from the current signer is missing. Also, it now covers the case when one of the commitments is missing. Improved unit test coverage to check all cases individually and then all of them together. This allowed to simplify deriveInterpolatingValue logic and skip the validation in this function as all the required validation happens earlier, in validateGroupCommitments.
pdyraga
commented
Jan 2, 2024
| nonce *Nonce, | ||
| commitments []*NonceCommitment, | ||
| ) (*big.Int, error) { | ||
| // TODO: validate number of commitments? |
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Let's look at it in a separate PR, where we figure out the coordinator's code.
pdyraga
changed the title
eth-r
approved these changes
Jan 4, 2024
| // challenge_input = group_comm_enc || group_public_key_enc || msg | ||
| // challenge = H2(challenge_input) | ||
| // return challenge | ||
| return s.ciphersuite.H2(groupCommitmentEncoded, publicKeyEncoded, message) |
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It is possible that some suites may use something weird for H2 which would be incompatible with this, but I think for the most part this is likely to be fine. Something we may want to consider is whether H2 should take in (Point, Point, []byte) arguments instead, but it shouldn't be a blocker.
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Depends on #7Round2implements the Round Two - Signature Share Generation phase from [FROST], section 5.2 Round Two - Signature Share Generation, based on @eth-r's prototype code.Note that
Round2code is not covered with unit tests. Those will be implemented for the protocol as a whole, in a separate PR, once the Coordinator code is ready.