KarpelesLab / tss-lib / 24250596740

77%

Build Type

push

github

Committed by MagicalTux

Commit Message

fix threshold subset signing by reindexing keys against current parties

The new ecdsatss/eddsatss signing paths indexed per-party slices (Ks,
BigXj, and for ECDSA NTildej/H1j/H2j/PaillierPKs) by the current-party
index but stored them in keygen-party order. When the signing committee
was a strict subset of the keygen parties, Lagrange interpolation and
MTA lookups used wrong slots and produced signatures that did not
verify under the master pubkey. The eddsatss resharing round1Old had
the same bug against OldParties.

The deprecated ecdsa/signing package handled this with
keygen.BuildLocalSaveDataSubset inside NewLocalPartyWithKDD; the port
dropped that step.

Add (*Key).SubsetForParties on both ecdsatss.Key and eddsatss.Key that
rebuilds the per-party slices by matching ShareID against the provided
sorted party IDs. Call it transparently at the top of NewSigning in both
packages and at the top of eddsatss.Resharing.round1Old. Replace
ecdsatss.Resharing.buildSubsetKey with a call to the shared method.

Cover the fix with TestKeygenAndSignStrictSubset in both packages —
4-party ECDSA keygen with a non-contiguous 2-party signing subset and
5-party EdDSA keygen with a non-contiguous 3-party subset — verifying
the resulting signature under the master pubkey via crypto/ecdsa.Verify
and edwards25519.VerifyRS respectively.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Coverage Stats

56 of 68 new or added lines in 6 files covered. (82.35%)

7 existing lines in 4 files now uncovered.

9722 of 12867 relevant lines covered (75.56%)

814.6 hits per line