v2.0.0: claims model - signed MMUR2 votes in a truth DB, merged view in a rebuildable cache DB; POST /api/claims, claims and merge routes, unsigned writes answer 410

internal/identity/identity.go

@@ -307,6 +307,30 @@ func Sign(id *Identity, bytes []byte) ([]byte, error) {
 	return sig.Serialize(), nil
 }
 
+// SignCompact is Sign with the 64-byte compact r||s encoding MMUR2 claims
+// use. decred's RFC 6979 signer always emits low-S, which MMUR2 requires.
+func SignCompact(id *Identity, bytes []byte) ([]byte, error) {
+	if id == nil {
+		return nil, errors.New("no identity loaded")
+	}
+	raw, err := hex.DecodeString(id.PrivateKeyHex)
+	if err != nil {
+		return nil, fmt.Errorf("decode private key: %w", err)
+	}
+	if len(raw) != 32 {
+		return nil, fmt.Errorf("private key length %d", len(raw))
+	}
+	priv := secp256k1.PrivKeyFromBytes(raw)
+	digest := sha256.Sum256(bytes)
+	sig := ecdsa.Sign(priv, digest[:])
+	r, s := sig.R(), sig.S()
+	out := make([]byte, 64)
+	rb, sb := r.Bytes(), s.Bytes()
+	copy(out[:32], rb[:])
+	copy(out[32:], sb[:])
+	return out, nil
+}
+
 // DeriveAEADKey derives the symmetric key used to encrypt private-tier
 // User Data Layer records. The KDF parameters (salt, info, length) are
 // fixed for the v1 wire format.