public static bool TrySignAdaptor(this ECPrivKey key, ReadOnlySpan <byte> msg32, ECPubKey adaptor, out SecpECDSAAdaptorSignature?adaptorSignature, out SecpECDSAAdaptorProof?proof)
{
if (key == null)
{
throw new ArgumentNullException(nameof(key));
}
if (adaptor == null)
{
throw new ArgumentNullException(nameof(adaptor));
}
if (msg32.Length < 32)
{
throw new ArgumentException(paramName: nameof(msg32), message: "msg32 should be at least 32 bytes");
}
var adaptor_ge = adaptor.Q;
var seckey32 = key.sec;
SHA256 sha = new SHA256();
sha.Write(msg32.Slice(0, 32));
Span <byte> buf33 = stackalloc byte[33];
Internals.secp256k1_dleq_serialize_point(buf33, adaptor_ge);
sha.Write(buf33);
sha.GetHash(buf33);
Span <byte> nonce32 = stackalloc byte[32];
nonce_function_dleq(buf33, key.sec, "ECDSAAdaptorNon", nonce32);
var k = new Scalar(nonce32);
if (k.IsZero)
{
adaptorSignature = default;
proof = default;
return(false);
}
var rpj = key.ctx.EcMultGenContext.MultGen(k);
/* 2. R = k*Y; */
var rj = adaptor_ge.MultConst(k, 256);
/* 4. [sic] proof = DLEQ_prove((G,R'),(Y, R)) */
if (!key.ctx.EcMultGenContext.secp256k1_dleq_proof("ECDSAAdaptorSig", k, adaptor_ge, out var dleq_proof_s, out var dleq_proof_e))
{
adaptorSignature = default;
proof = default;
return(false);
}
/* 5. s' = k⁻¹(H(m) + x_coord(R)x) */
var r = rj.ToGroupElement();
var msg = new Scalar(msg32);
if (!secp256k1_ecdsa_adaptor_sign_helper(msg, k, r, key.sec, out var sp))
{
k = default;
adaptorSignature = default;
proof = default;
return(false);
}
/* 6. return (R, R', s', proof) */
var rp = rpj.ToGroupElement();
proof = new SecpECDSAAdaptorProof(rp, dleq_proof_s, dleq_proof_e);
adaptorSignature = new SecpECDSAAdaptorSignature(r, sp);
k = default;
return(true);
}
public static bool SigVerify(this ECPubKey pubKey, SecpECDSAAdaptorSignature sig, SecpECDSAAdaptorProof proof, ReadOnlySpan <byte> msg32, ECPubKey adaptor)
{
if (pubKey == null)
{
throw new ArgumentNullException(nameof(pubKey));
}
if (adaptor == null)
{
throw new ArgumentNullException(nameof(adaptor));
}
if (msg32.Length < 32)
{
throw new ArgumentException(paramName: nameof(msg32), message: "msg32 should be at least 32 bytes");
}
if (sig == null)
{
throw new ArgumentNullException(nameof(sig));
}
var adaptor_ge = adaptor.Q;
if (!secp256k1_dleq_verify(pubKey.ctx.EcMultContext, "ECDSAAdaptorSig", proof.s, proof.e, proof.rp, adaptor_ge, sig.r))
{
return(false);
}
/* 2. return x_coord(R') == x_coord(s'⁻¹(H(m) * G + x_coord(R) * X)) */
var q = pubKey.Q;
var msg = new Scalar(msg32);
if (!pubKey.ctx.secp256k1_ecdsa_adaptor_sig_verify_helper(sig.r.x.ToScalar(), sig.sp, q, msg, out var rhs))
{
return(false);
}
var lhs = proof.rp.ToGroupElementJacobian();
rhs = rhs.Negate();
lhs = lhs.AddVariable(rhs, out _);
return(lhs.IsInfinity);
}