public string Encrypt(KeyPair encryptionKeyPair, string plainText)
{
//use THEIR public key to encrypt
_rsaCryptoServiceProvider.FromXmlString(encryptionKeyPair.Public.Key);
//Get Modulus Size and compare it to length of PlainText
// If Length of PlainText > (Modulus Size - 11), then PlainText will need to be broken into segments of size (Modulus Size - 11)
// Each of these segments will be encrypted separately
// and will return encrypted strings equal to the Modulus Size (with at least 11 bytes of padding)
// When decrypting, if the EncryptedText string > Modulus size, it will be split into segments of size equal to Modulus Size
// Each of these EncryptedText segments will be decrypted individually with the resulting PlainText segments re-assembled.
var blockSize = GetModulusSize() - 11;
var plainStream = new MemoryStream(TextHelpers.ClearTextToClearBytes(plainText));
var cipherStream = new MemoryStream();
var buffer = new byte[blockSize];
while (plainStream.Read(buffer, 0, blockSize) > 0)
{
var c = _rsaCryptoServiceProvider.Encrypt(buffer, false);
cipherStream.Write(c, 0, c.Length);
}
var cipherBytes = cipherStream.ToArray();
return(TextHelpers.CipherBytesToCipherText(cipherBytes));
}
public string Sign(KeyPair signingKeyPair, string text)
{
//Use PrivateKey to sign
_rsaCryptoServiceProvider.FromXmlString(signingKeyPair.Private.Key);
var signedData = _rsaCryptoServiceProvider.SignData(TextHelpers.ClearTextToClearBytes(text), HashAlgorithm.Create());
var signature = TextHelpers.CipherBytesToCipherText(signedData);
return(string.Format("{0}<signature>{1}</signature>", text, signature));
}
public bool Authenticate(KeyPair authenticationKeyPair, string signedText)
{
_rsaCryptoServiceProvider.FromXmlString(authenticationKeyPair.Public.Key);
string signature = CryptoHelpers.ExtractSignature(signedText);
string message = CryptoHelpers.StripSignature(signedText);
if (string.IsNullOrEmpty(signature))
{
throw new Exception("Digital signature is missing or not formatted properly.");
}
var bytes = TextHelpers.ClearTextToClearBytes(message);
var sigbytes = TextHelpers.CipherTextToCipherBytes(signature);
return(_rsaCryptoServiceProvider.VerifyData(bytes, HashAlgorithm.Create(), sigbytes));
}
