public EncryptedPacket EncryptData(byte[] original, RSAWithRSAParameterKey rsaParams, DigitalSignatureFuncs digitalSignature)
{
// Generate our session key
var sessionKey = _aes.GenerateRandomNumber(32);
// Create the encrypted packet and generate the IV
var encryptedPacket = new EncryptedPacket
{
IV = _aes.GenerateRandomNumber(16)
};
// Encrypt our data with AES
encryptedPacket.EncryptedData = _aes.Encrypt(original, sessionKey, encryptedPacket.IV);
// Encrypt the session key with RSA
encryptedPacket.EncryptedSessionKey = rsaParams.EncryptData(sessionKey);
// Calculate a HMAC
encryptedPacket.HMAC = HMac.ComputeHMACSha256(encryptedPacket.EncryptedData, sessionKey);
// Generate digital signature of packet to send
encryptedPacket.Signature = digitalSignature.SignData(encryptedPacket.HMAC);
return(encryptedPacket);
}
public byte[] DecryptData(EncryptedPacket encryptedPacket, RSAWithRSAParameterKey rsaParams, DigitalSignatureFuncs digitalSignature)
{
// Decrypt AES Key with RSA
var decryptedSessionKey = rsaParams.DecryptData(encryptedPacket.EncryptedSessionKey);
// Integrity + Signature Check
var hmacToCheck = HMac.ComputeHMACSha256(encryptedPacket.EncryptedData, decryptedSessionKey);
if (!Compare(encryptedPacket.HMAC, hmacToCheck))
{
throw new CryptographicException("HMAC for decryption does not match encrypted package HMAC code received. This means the message has been tampered with.");
}
if (!digitalSignature.VerifySignature(encryptedPacket.HMAC, encryptedPacket.Signature))
{
throw new CryptographicException("Digital Signature of document cannot be verified.");
}
// Decrypt our data with AES using the decryptedSessionKey
return(_aes.Decrypt(encryptedPacket.EncryptedData, decryptedSessionKey, encryptedPacket.IV));
}