public static string GetSignature(string unsignedMessage, string p, string g, string x)
{
// Trim message
unsignedMessage = unsignedMessage.Trim();
var sha = new SHA256();
BigInteger hash = sha.GetMessageDigestToBigInteger(unsignedMessage);
string signature = SiGamalGenerator.signature(BigInteger.Parse(p), BigInteger.Parse(g), BigInteger.Parse(x), hash);
return(signature);
}
/// <summary>
/// Verify the authenticity and integrity of a string which contains a message
/// along with its signature.
/// </summary>
/// <param name="signedMessage">A string containing a message and its signature</param>
/// <returns>True if the signature matches, false if it doesn't.</returns>
public static bool VerifySignedMessage(string signedMessage, string p, string g, string y)
{
string body = signedMessage.Substring(0, signedMessage.IndexOf("\n\n<sign>")).Trim();
string rs = signedMessage.Substring(signedMessage.IndexOf("<sign>"));
rs = rs.Substring(6);
rs = rs.Substring(0, rs.IndexOf("<sign>"));
BigInteger r = BigInteger.Parse("0" + rs.Substring(0, rs.IndexOf('-')), System.Globalization.NumberStyles.HexNumber);
BigInteger s = BigInteger.Parse("0" + rs.Substring(rs.IndexOf('-') + 1), System.Globalization.NumberStyles.HexNumber);
System.Diagnostics.Debug.WriteLine(r);
System.Diagnostics.Debug.WriteLine(s);
SHA256 sha = new SHA256();
bool isValid = SiGamalGenerator.verification(r, s, BigInteger.Parse(g), sha.GetMessageDigestToBigInteger(body), BigInteger.Parse(y), BigInteger.Parse(p));
return(isValid);
}