public byte[] DecryptData(EncryptedPacket encryptedPacket, RSAWithRSAParameterKey rsaParams,
DigitalSignature digitalSignature)
{
var decryptedSessionKey = rsaParams.DecryptData(encryptedPacket.EncryptedSessionKey);
using (var hmac = new HMACSHA256(decryptedSessionKey))
{
var hmacToCheck = hmac.ComputeHash(Combine(encryptedPacket.EncryptedData, encryptedPacket.Iv));
if (!Compare(encryptedPacket.Hmac, hmacToCheck))
{
throw new CryptographicException(
"HMAC for decryption does not match encrypted packet.");
}
}
if (!digitalSignature.VerifySignature(encryptedPacket.Hmac,
encryptedPacket.Signature))
{
throw new CryptographicException(
"Digital Signature can not be verified.");
}
var decryptedData = _aes.Decrypt(encryptedPacket.EncryptedData, decryptedSessionKey,
encryptedPacket.Iv);
return(decryptedData);
}
public EncryptedPacket EncryptData(byte[] original, RSAWithRSAParameterKey rsaParams,
DigitalSignature digitalSignature)
{
var sessionKey = _aes.GenerateRandomNumber(32);
var encryptedPacket = new EncryptedPacket {
Iv = _aes.GenerateRandomNumber(16)
};
encryptedPacket.EncryptedData = _aes.Encrypt(original, sessionKey, encryptedPacket.Iv);
encryptedPacket.EncryptedSessionKey = rsaParams.EncryptData(sessionKey);
using (var hmac = new HMACSHA256(sessionKey))
{
encryptedPacket.Hmac = hmac.ComputeHash(Combine(encryptedPacket.EncryptedData, encryptedPacket.Iv));
}
encryptedPacket.Signature = digitalSignature.SignData(encryptedPacket.Hmac);
return(encryptedPacket);
}
