Make Cross-Compilable: Port PubKey Recovery to Go #5
Description
It's not Public Keys that are used as Addresses, but rather PubKeyHashes.
Since Go's standard library doesn't include a function to reverse a Message + Signature to a Public Key, it's not possible to verify a PubKeyHash against a signature natively in Go.
- sha3 "golang.org/x/crypto/sha3"
- sign
- recover
However, it seems that the primarily function that's causing all of the headache with cross compilation has been written natively in C#, and would not be difficult to port to Go.
public static ECPoint Recover(byte[] hash, byte[] sigBytes, int rec)
{
BigInteger r = new BigInteger(1, sigBytes, 0, 32);
BigInteger s = new BigInteger(1, sigBytes, 32, 32);
BigInteger[] sig = new BigInteger[]{ r, s };
ECPoint Q = ECDSA_SIG_recover_key_GFp(sig, hash, rec, true);
return Q;
}
public static ECPoint ECDSA_SIG_recover_key_GFp(BigInteger[] sig, byte[] hash, int recid, bool check)
{
X9ECParameters ecParams = Org.BouncyCastle.Asn1.Sec.SecNamedCurves.GetByName("secp256k1");
int i = recid / 2;
Console.WriteLine("r: "+ToHex(sig[0].ToByteArrayUnsigned()));
Console.WriteLine("s: "+ToHex(sig[1].ToByteArrayUnsigned()));
BigInteger order = ecParams.N;
BigInteger field = (ecParams.Curve as FpCurve).Q;
BigInteger x = order.Multiply(new BigInteger(i.ToString())).Add(sig[0]);
if (x.CompareTo(field) >= 0) throw new Exception("X too large");
Console.WriteLine("Order: "+ToHex(order.ToByteArrayUnsigned()));
Console.WriteLine("Field: "+ToHex(field.ToByteArrayUnsigned()));
byte[] compressedPoint = new Byte[x.ToByteArrayUnsigned().Length+1];
compressedPoint[0] = (byte) (0x02+(recid%2));
Buffer.BlockCopy(x.ToByteArrayUnsigned(), 0, compressedPoint, 1, compressedPoint.Length-1);
ECPoint R = ecParams.Curve.DecodePoint(compressedPoint);
Console.WriteLine("R: "+ToHex(R.GetEncoded()));
if (check)
{
ECPoint O = R.Multiply(order);
if (!O.IsInfinity) throw new Exception("Check failed");
}
int n = (ecParams.Curve as FpCurve).Q.ToByteArrayUnsigned().Length*8;
BigInteger e = new BigInteger(1, hash);
if (8*hash.Length > n)
{
e = e.ShiftRight(8-(n & 7));
}
e = BigInteger.Zero.Subtract(e).Mod(order);
BigInteger rr = sig[0].ModInverse(order);
BigInteger sor = sig[1].Multiply(rr).Mod(order);
BigInteger eor = e.Multiply(rr).Mod(order);
ECPoint Q = ecParams.G.Multiply(eor).Add(R.Multiply(sor));
Console.WriteLine("n: "+n);
Console.WriteLine("e: "+ToHex(e.ToByteArrayUnsigned()));
Console.WriteLine("rr: "+ToHex(rr.ToByteArrayUnsigned()));
Console.WriteLine("sor: "+ToHex(sor.ToByteArrayUnsigned()));
Console.WriteLine("eor: "+ToHex(eor.ToByteArrayUnsigned()));
Console.WriteLine("Q: "+ToHex(Q.GetEncoded()));
return Q;
}