/// <summary>
/// Verifies a signature of <paramref name="Data"/> made by the EdDSA 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="Signature">Signature</param>
/// <returns>If the signature is valid.</returns>
public static bool Verify(Stream Data, byte[] PublicKey, HashFunctionStream HashFunction,
EdwardsCurveBase Curve, byte[] Signature)
{
try
{
int ScalarBytes = Signature.Length;
if ((ScalarBytes & 1) != 0)
{
return(false);
}
ScalarBytes >>= 1;
byte[] R = new byte[ScalarBytes];
Array.Copy(Signature, 0, R, 0, ScalarBytes);
PointOnCurve r = Decode(R, Curve);
byte[] S = new byte[ScalarBytes];
Array.Copy(Signature, ScalarBytes, S, 0, ScalarBytes);
BigInteger s = EllipticCurve.ToInt(S);
byte[] h;
if (s >= Curve.Order)
{
return(false);
}
using (TemporaryFile TempFile = new TemporaryFile()) // dom2(F, C) = blank string
{
TempFile.Write(R, 0, ScalarBytes);
TempFile.Write(PublicKey, 0, ScalarBytes);
Data.Position = 0;
Data.CopyTo(TempFile); // PH(M)=M
TempFile.Position = 0;
h = HashFunction(TempFile);
}
BigInteger k = BigInteger.Remainder(EllipticCurve.ToInt(h), Curve.Order);
PointOnCurve P1 = Curve.ScalarMultiplication(s, Curve.BasePoint, false);
PointOnCurve P2 = Curve.ScalarMultiplication(k, Curve.Decode(PublicKey), false);
Curve.AddTo(ref P2, r);
P1.Normalize(Curve);
P2.Normalize(Curve);
return(P1.Equals(P2));
}
catch (ArgumentException)
{
return(false);
}
}
private byte[] H_dom4(Stream Data)
{
using (TemporaryFile TempFile = new TemporaryFile())
{
TempFile.Write(preamble, 0, 8);
TempFile.WriteByte(0); // x=phflag=0
TempFile.WriteByte(0); // y=context=empty string
Data.Position = 0;
Data.CopyTo(TempFile);
TempFile.Position = 0;
return(this.shake256_114.ComputeVariable(TempFile));
}
}
/// <summary>
/// Signs data using the EdDSA algorithm.
/// </summary>
/// <param name="Data">Data to be signed.</param>
/// <param name="PrivateKey">Private key.</param>
/// <param name="Prefix">Prefix</param>
/// <param name="HashFunction">Hash function to use</param>
/// <param name="Curve">Elliptic curve</param>
/// <returns>Signature</returns>
public static byte[] Sign(Stream Data, byte[] PrivateKey, byte[] Prefix,
HashFunctionStream HashFunction, EdwardsCurveBase Curve)
{
// 5.1.6 of RFC 8032
int ScalarBytes = PrivateKey.Length;
if (Prefix.Length != ScalarBytes)
{
throw new ArgumentException("Invalid prefix.", nameof(Prefix));
}
BigInteger a = EllipticCurve.ToInt(PrivateKey);
PointOnCurve P = Curve.ScalarMultiplication(PrivateKey, Curve.BasePoint, true);
byte[] A = Encode(P, Curve);
byte[] h;
using (TemporaryFile TempFile = new TemporaryFile()) // dom2(F, C) = blank string
{
TempFile.Write(Prefix, 0, ScalarBytes); // prefix
Data.Position = 0;
Data.CopyTo(TempFile); // PH(M)=M
TempFile.Position = 0;
h = HashFunction(TempFile);
}
BigInteger r = BigInteger.Remainder(EllipticCurve.ToInt(h), Curve.Order);
PointOnCurve R = Curve.ScalarMultiplication(r, Curve.BasePoint, true);
byte[] Rs = Encode(R, Curve);
using (TemporaryFile TempFile = new TemporaryFile()) // dom2(F, C) = blank string
{
TempFile.Write(Rs, 0, ScalarBytes);
TempFile.Write(A, 0, ScalarBytes);
Data.Position = 0;
Data.CopyTo(TempFile); // PH(M)=M
TempFile.Position = 0;
h = HashFunction(TempFile);
}
BigInteger k = BigInteger.Remainder(EllipticCurve.ToInt(h), Curve.Order);
BigInteger s = Curve.ModulusN.Add(r, Curve.ModulusN.Multiply(k, a));
byte[] Bin = s.ToByteArray();
if (Bin.Length != ScalarBytes)
{
Array.Resize <byte>(ref Bin, ScalarBytes);
}
byte[] Signature = new byte[ScalarBytes << 1];
Array.Copy(Rs, 0, Signature, 0, ScalarBytes);
Array.Copy(Bin, 0, Signature, ScalarBytes, ScalarBytes);
return(Signature);
}
