/// <summary>
/// Verifies a signature of <paramref name="Data"/> made by the ECDSA algorithm.
/// </summary>
/// <param name="Data">Payload to sign.</param>
/// <param name="PublicKey">Public Key of the entity that generated the signature.</param>
/// <param name="HashFunction">Hash function to use.</param>
/// <param name="Curve">Elliptic curve</param>
/// <param name="ScalarBytes">Number of bytes to use for scalars.</param>
/// <param name="MsbMask">Mask for most significant byte.</param>
/// <param name="Signature">Signature</param>
/// <returns>If the signature is valid.</returns>
public static bool Verify(byte[] Data, byte[] PublicKey, HashFunction HashFunction,
int ScalarBytes, byte MsbMask, PrimeFieldCurve Curve, byte[] Signature)
{
int c = Signature.Length;
if (c != ScalarBytes << 1)
{
return(false);
}
c >>= 1;
byte[] Bin = new byte[c];
Array.Copy(Signature, 0, Bin, 0, c);
BigInteger r = EllipticCurve.ToInt(Bin);
Bin = new byte[c];
Array.Copy(Signature, c, Bin, 0, c);
BigInteger s = EllipticCurve.ToInt(Bin);
PointOnCurve PublicKeyPoint = Curve.Decode(PublicKey);
if (!PublicKeyPoint.NonZero || r.IsZero || s.IsZero || r >= Curve.Order || s >= Curve.Order)
{
return(false);
}
BigInteger e = CalcE(Data, HashFunction, ScalarBytes, MsbMask);
BigInteger w = Curve.ModulusN.Invert(s);
BigInteger u1 = Curve.ModulusN.Multiply(e, w);
BigInteger u2 = Curve.ModulusN.Multiply(r, w);
PointOnCurve P2 = Curve.ScalarMultiplication(u1, Curve.BasePoint, true);
PointOnCurve P3 = Curve.ScalarMultiplication(u2, PublicKeyPoint, true);
Curve.AddTo(ref P2, P3);
if (!P2.NonZero)
{
return(false);
}
P2.Normalize(Curve);
BigInteger Compare = BigInteger.Remainder(P2.X, Curve.Order);
if (Compare.Sign < 0)
{
Compare += Curve.Order;
}
return(Compare == r);
}
/// <summary>
/// Signs data using the ECDSA algorithm.
/// </summary>
/// <param name="Data">Data to be signed.</param>
/// <param name="PrivateKey">Private key.</param>
/// <param name="HashFunction">Hash function to use</param>
/// <param name="ScalarBytes">Number of bytes to use for scalars.</param>
/// <param name="MsbMask">Mask for most significant byte.</param>
/// <param name="Curve">Elliptic curve</param>
/// <returns>Signature</returns>
public static byte[] Sign(byte[] Data, byte[] PrivateKey, HashFunction HashFunction,
int ScalarBytes, byte MsbMask, PrimeFieldCurve Curve)
{
BigInteger e = CalcE(Data, HashFunction, ScalarBytes, MsbMask);
BigInteger r, s, PrivateKeyInt = EllipticCurve.ToInt(PrivateKey);
PointOnCurve P1;
byte[] k;
do
{
do
{
k = Curve.GenerateSecret();
P1 = Curve.ScalarMultiplication(k, Curve.BasePoint, true);
}while (P1.IsXZero);
r = BigInteger.Remainder(P1.X, Curve.Order);
s = Curve.ModulusN.Divide(Curve.ModulusN.Add(e,
Curve.ModulusN.Multiply(r, PrivateKeyInt)), EllipticCurve.ToInt(k));
}while (s.IsZero);
if (r.Sign < 0)
{
r += Curve.Prime;
}
P1.Normalize(Curve);
byte[] Signature = new byte[ScalarBytes << 1];
byte[] S = r.ToByteArray();
if (S.Length != ScalarBytes)
{
Array.Resize <byte>(ref S, ScalarBytes);
}
Array.Copy(S, 0, Signature, 0, ScalarBytes);
S = s.ToByteArray();
if (S.Length != ScalarBytes)
{
Array.Resize <byte>(ref S, ScalarBytes);
}
Array.Copy(S, 0, Signature, ScalarBytes, ScalarBytes);
return(Signature);
}
