public byte[] DecryptDataWithSignature(EncryptedPacket EP, RsaWithRsaParameterKey rsaParams, DigitalSignatures DS)
{
// Receiver decrypts AES session key with RSA
byte[] decryptedSessionKey = rsaParams.DecryptData(EP.EncryptedSessionKey);
// Receiver compares
using (HMACSHA256 hmac = new HMACSHA256(decryptedSessionKey))
{
byte[] hmacToCheck = hmac.ComputeHash(EP.EncryptedData);
if (!CompareHashes(EP.Hmac, hmacToCheck))
{
throw new CryptographicException("HMAC for decryption does not match encrypted packet HMAC");
}
if (!DS.VerifySignature(EP.Hmac, EP.Signature))
{
throw new CryptographicException("Digital Signature cannot be verified");
}
}
// Receiver decrypts the data wuth AES using the decrypted session key
byte[] decryptedData = _cryptographyExample.DecryptUsingAES(EP.EncryptedData, decryptedSessionKey, EP.IV);
return(decryptedData);
}
private static void RunDigitalSignature()
{
Console.WriteLine("Digital Signatures started");
Console.WriteLine();
Console.WriteLine(String.Format("Message before encryption: {0}", _signatureMessage));
byte[] messageToSign = Encoding.UTF8.GetBytes(_signatureMessage);
byte[] hashedDocument;
using (SHA256 sha256 = SHA256.Create())
{
hashedDocument = sha256.ComputeHash(messageToSign);
}
DigitalSignatures DS = new DigitalSignatures();
DS.AssignNewKey();
byte[] signature = DS.SignData(hashedDocument);
Console.WriteLine(String.Format("Digital Signature: {0}", Encoding.UTF8.GetString(signature)));
bool isSignatureVerified = DS.VerifySignature(hashedDocument, signature);
Console.WriteLine(String.Format("Verify Signature Results: {0}", isSignatureVerified.ToString()));
Console.WriteLine();
Console.WriteLine("Digital Signatures ended");
}