private BigInteger ComputeSchnorrE(byte[] rba, EllipticCurvePoint P, byte[] hash)
{
// Compute "tagged hash":
// tagHash = Sha256(tagstring)
// msg = R.X | P.X | hash
// return sha256(tagHash | tagHash | msg)
using Sha256 sha = new Sha256();
byte[] pba = P.X.ToByteArray(true, true);
// TODO: change all these BigIntegers to ModUint256 type so that it doesn't need length checks,...!
byte[] pubBa = new byte[32];
Buffer.BlockCopy(pba, 0, pubBa, 32 - pba.Length, pba.Length);
BigInteger e = sha.ComputeTaggedHash_BIPSchnorr(rba, pubBa, hash).ToBigInt(true, true) % curve.N;
return(e);
}
