v3.0.1 - EdDSA Child Key Derivation

Highlights

This release adds EdDSA Child Key Derivation (CKD) so HD-wallet–style key
derivation works for Ed25519-based chains (e.g. Solana), and restores
pre-v3.0.0 CKD behavior needed for Edwards curves.

Features

• EdDSA signing with HD key derivation — eddsa/signing can now sign with
  a derived child key. Adds key_derivation_util.go
  (UpdatePublicKeyAndAdjustBigXj), wires the derivation delta into the local
  party and round_1, and adds an end-to-end test
  (TestE2EConcurrentWithHDDerive). Ported from fystack/tss-lib onto
  bnb-chain v3.0.0; the unrelated range-proof / Feldman-VSS changes and the
  ExtendedKey refactor from upstream were intentionally dropped, since v3.0.0
  already handles multi-curve internally via crypto.NewECPoint.

Fixes

• CKD: reduce IL modulo N before the range check — restores the
  pre-v3.0.0 behavior of applying ilNum.Mod(N) before the range check in
  DeriveChildKey. v3.0.0 made the check strict per BIP-32, which mandates
  retrying with the next index when IL >= N. This library does not implement
  retry, and on Edwards curves N ≈ 2^252 so ~94% of raw 256-bit HMAC outputs
  exceed N — the strict check made EdDSA CKD effectively unusable.
  Trade-off: introduces a ~2^-4 modular bias on derived child public keys; the
  bias is washed out on private shares by the uniform parent share, so it does
  not enable key recovery or forgery, and it preserves address compatibility
  with wallets derived under prior library versions.

Maintenance

• gofmt formatting fixes in common/constant_time.go and
  crypto/paillier/paillier.go.

Verification

• crypto/ckd: PASS (BIP-32 test vectors for secp256k1)
• eddsa/signing TestE2EConcurrentWithHDDerive: PASS
• ecdsa/signing TestE2EWithHDKeyDerivation: PASS

Commits

• 26baa22 add ecdsa derive signing logical
• 2f5ab80 change priv version
• 9751c3a ckd: reduce IL modulo N before range check
• 8146a64 Fix format

EDdSA child key derivation

Merge pull request #3 from fystack/revert

Restore Security Checks Removed in EdDSA CKD Commits