/// <summary>
/// Same function as EncryptMessage, but signs the message first
/// </summary>
/// <param name="message">Message to be encrypted</param>
/// <param name="publicKeyString">Public key of the recipient</param>
/// <param name="password">Password needed to use the user's private key for the signature process</param>
/// <returns>
/// The formatted encrypted message with all the non-secure data added to it, in addition to the digital
/// signature
/// </returns>
public static string EncryptAndSignMessage(string message, string publicKeyString, string password)
{
string sign;
RSAParameters key = KeyVault.RetrieveRSAParams(password);
RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
rsa.ImportParameters(key);
using (StringWriter sw = new StringWriter())
{
sw.WriteLine(signatureHeader);
sw.WriteLine(Convert.ToBase64String(DigitalSignature.SignMessage(key, message)));
sw.WriteLine(signatureTail);
sw.WriteLine(pubKeyHeader);
sw.WriteLine(KeyVault.SerializeRSAParams(rsa.ExportParameters(false)));
sw.WriteLine(pubKeyTail);
sign = sw.ToString();
}
return(EncryptMessage(message, publicKeyString) + sign);
}
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(encryptedPacket.EncryptedData);
if (!Compare(encryptedPacket.Hmac, hmacToCheck))
{
throw new CryptographicException("HMAC for encryption does not match with encrypted packet");
}
if (!digitalSignature.VerifySignature(encryptedPacket.Hmac, hmacToCheck))
{
throw new CryptographicException("Digital Signature can not be verified");
}
}
var decryptedData = _aes.Decrypt(encryptedPacket.EncryptedData, decryptedSessionKey, encryptedPacket.Iv);
return(decryptedData);
}
/// <summary>
/// Decrypts a given message using the user's password-protected private key
/// </summary>
/// <param name="cipherMessage">The message to be decrypted</param>
/// <param name="password">The user's password used to retrieve the user's private key</param>
/// <returns>Decrypted message</returns>
public static string DecryptMessage(string cipherMessage, string password)
{
bool isSigned = false;
string encryptedCryptKey;
string encryptedAuthKey;
string message;
string signature;
string pubKey = null;
using (StringReader sr = new StringReader(cipherMessage))
{
string line;
while ((line = sr.ReadLine()) != null)
{
if (line == greeting)
{
break;
}
}
while ((line = sr.ReadLine()) != null)
{
if (line == cryptKeyHeader)
{
break;
}
}
encryptedCryptKey = sr.ReadLine();
while ((line = sr.ReadLine()) != null)
{
if (line == authKeyHeader)
{
break;
}
}
encryptedAuthKey = sr.ReadLine();
while ((line = sr.ReadLine()) != null)
{
if (line == messageHeader)
{
break;
}
}
message = sr.ReadLine();
while ((line = sr.ReadLine()) != null)
{
if (line == signatureHeader)
{
isSigned = true;
break;
}
}
signature = sr.ReadLine();
while ((line = sr.ReadLine()) != null)
{
if (line == pubKeyHeader)
{
while ((line = sr.ReadLine()) != pubKeyTail)
{
pubKey += line;
}
}
}
}
while (encryptedAuthKey.Length % 4 != 0)
{
encryptedAuthKey += "=";
}
while (signature != null && signature.Length % 4 != 0)
{
signature += "=";
}
while (encryptedCryptKey.Length % 4 != 0)
{
encryptedCryptKey += "=";
}
while (message.Length % 4 != 0)
{
message += "=";
}
RSAParameters keys = KeyVault.RetrieveRSAParams(password);
byte[] encryptedCryptKeyBytes = Convert.FromBase64String(encryptedCryptKey);
byte[] encryptedAuthKeyBytes = Convert.FromBase64String(encryptedAuthKey);
byte[] cryptKey = RSAEncryption.DecryptRSA(encryptedCryptKeyBytes, keys);
byte[] authKey = RSAEncryption.DecryptRSA(encryptedAuthKeyBytes, keys);
string plainTextMessage = AESThenHMAC.Decrypt(message, cryptKey, authKey);
if (isSigned)
{
RSAParameters pubkey = KeyVault.DeserializeRSAParams(pubKey);
if (!DigitalSignature.VerifySignature(pubkey, plainTextMessage, signature))
{
string warning = "WARNING: this message appears to have a wrong digital signature.\r\n";
plainTextMessage = warning + plainTextMessage;
}
else
{
string success = "This message is digitally signed properly.\r\n";
plainTextMessage = success + plainTextMessage;
}
}
return(plainTextMessage);
}
public EncryptedPacket EncryptData(byte[] original, RSAWithRSAParameterKey rsaParams, DigitalSignature signature)
{
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(encryptedPacket.EncryptedData);
}
encryptedPacket.Signature = signature.SignData(encryptedPacket.Hmac);
return(encryptedPacket);
}
