public string DecryptAndVerifySignature(Message message, string senderPublicKey)
{
// Decrypt keys using recipient's private key
byte[] key = _rsa.Decrypt(message.Key, false);
byte[] iv = _rsa.Decrypt(message.IV, false);
// Get sender's public key
var senderRsa = new RSACryptoServiceProvider();
senderRsa.FromXmlString(senderPublicKey);
// Decrypt the cipher text using symmetrical encryption
var alg = new RijndaelManaged { Key = key, IV = iv };
var cryptor = new SymCrypt(alg);
byte[] clearTextBytes = cryptor.Decrypt(message.Data);
// Verify digital signature using the sender's public key.
bool verified = verifySignature(clearTextBytes, message.Signature, senderRsa);
string clearText = (new UTF8Encoding()).GetString(clearTextBytes);
return verified ? clearText : null;
}
public Message SignAndEncrypt(string message, string receiverPublicKey)
{
// convert message in bytes
byte[] messageBytes = (new UTF8Encoding()).GetBytes(message);
// Sign the clear text using the sender's private key
byte[] signature = signMessage(messageBytes);
var result = new Message { Signature = signature };
// Encrypt the clear text using symmetrical encryption
var cryptor = new SymCrypt(new RijndaelManaged());
byte[] encryptedData = cryptor.Encrypt(messageBytes);
result.Data = encryptedData;
// Get recipient's public key
var receiverRsa = new RSACryptoServiceProvider();
receiverRsa.FromXmlString(receiverPublicKey);
// Encrypt the encryption keys using the receiver's public key.
result.Key = receiverRsa.Encrypt(cryptor.Key, false);
result.IV = receiverRsa.Encrypt(cryptor.Iv, false);
return result;
}