/// <summary>
/// Check that this is correct public key.
/// </summary>
/// <remarks>
/// This method can be used to verify that public and private key are on the curve.
/// </remarks>
public static void Validate(GXPublicKey publicKey)
{
if (publicKey == null)
{
throw new ArgumentNullException("Invalid public key.");
}
GXByteBuffer bb = new GXByteBuffer();
bb.Set(publicKey.RawValue);
int size = SchemeSize(publicKey.Scheme);
GXBigInteger x = new GXBigInteger(bb.SubArray(1, size));
GXBigInteger y = new GXBigInteger(bb.SubArray(1 + size, size));
GXCurve curve = new GXCurve(publicKey.Scheme);
y.Multiply(y);
y.Mod(curve.P);
GXBigInteger tmpX = new GXBigInteger(x);
tmpX.Multiply(x);
tmpX.Mod(curve.P);
tmpX.Add(curve.A);
tmpX.Multiply(x);
tmpX.Add(curve.B);
tmpX.Mod(curve.P);
if (y.Compare(tmpX) != 0)
{
throw new ArgumentException("Public key validate failed. Public key is not valid ECDSA public key.");
}
}
/// <summary>
/// Get public key from private key.
/// </summary>
/// <param name="scheme">Used scheme.</param>
/// <param name="privateKey">Private key bytes.</param>
/// <returns>Public key.</returns>
public GXPublicKey GetPublicKey()
{
GXBigInteger secret = new GXBigInteger(RawValue);
GXCurve curve = new GXCurve(Scheme);
GXEccPoint p = new GXEccPoint(curve.G.x, curve.G.y, new GXBigInteger(1));
p = GXEcdsa.JacobianMultiply(p, secret, curve.N, curve.A, curve.P);
GXEcdsa.FromJacobian(p, curve.P);
GXByteBuffer key = new GXByteBuffer(65);
//Public key is un-compressed format.
key.SetUInt8(4);
byte[] tmp = p.x.ToArray();
key.Set(tmp, tmp.Length % 32, 32);
tmp = p.y.ToArray();
key.Set(tmp, tmp.Length % 32, 32);
return(GXPublicKey.FromRawBytes(key.Array()));
}
/// <summary>
/// Get public key from private key.
/// </summary>
/// <param name="scheme">Used scheme.</param>
/// <param name="privateKey">Private key bytes.</param>
/// <returns>Public key.</returns>
public GXPublicKey GetPublicKey()
{
if (publicKey == null)
{
GXBigInteger pk = new GXBigInteger(RawValue);
GXCurve curve = new GXCurve(Scheme);
GXEccPoint p = new GXEccPoint(curve.G.x, curve.G.y, new GXBigInteger(1));
p = GXEcdsa.JacobianMultiply(p, pk, curve.N, curve.A, curve.P);
GXEcdsa.FromJacobian(p, curve.P);
GXByteBuffer key = new GXByteBuffer(65);
//Public key is un-compressed format.
key.SetUInt8(4);
byte[] tmp = p.x.ToArray();
int size = Scheme == Ecc.P256 ? 32 : 48;
key.Set(tmp, tmp.Length % size, size);
tmp = p.y.ToArray();
key.Set(tmp, tmp.Length % size, size);
publicKey = GXPublicKey.FromRawBytes(key.Array());
}
return(publicKey);
}
/// <summary>
/// Generate shared secret from public and private key.
/// </summary>
/// <param name="publicKey">Public key.</param>
/// <returns>Generated secret.</returns>
public byte[] GenerateSecret(GXPublicKey publicKey)
{
if (PrivateKey == null)
{
throw new ArgumentNullException("Invalid private key.");
}
if (PrivateKey.Scheme != publicKey.Scheme)
{
throw new ArgumentNullException("Private key scheme is different than public key.");
}
GXByteBuffer bb = new GXByteBuffer();
bb.Set(publicKey.RawValue);
int size = SchemeSize(PrivateKey.Scheme);
GXBigInteger x = new GXBigInteger(bb.SubArray(1, size));
GXBigInteger y = new GXBigInteger(bb.SubArray(1 + size, size));
GXBigInteger pk = new GXBigInteger(PrivateKey.RawValue);
GXCurve curve = new GXCurve(PrivateKey.Scheme);
GXEccPoint p = new GXEccPoint(x, y, new GXBigInteger(1));
p = JacobianMultiply(p, pk, curve.N, curve.A, curve.P);
FromJacobian(p, curve.P);
return(p.x.ToArray());
}
private GXEcdsa(Ecc scheme)
{
curve = new GXCurve(scheme);
}