/// <summary>
/// Decrypts a string
/// </summary>
/// <param name="CipherText">Text to be decrypted</param>
/// <param name="Password">Password to decrypt with</param>
/// <param name="Salt">Salt to decrypt with</param>
/// <param name="CryptoType">Can be either AES, 3DES, RJINDAEL</param>
/// <param name="PasswordIterations">Number of iterations to do</param>
/// <param name="InitialVector">Needs to be 16 ASCII characters long for SHA1, 32 ASCII characters long for SHA256</param>
/// <param name="KeySize">Can be 128, 192, or 256</param>
/// <returns>A decrypted string</returns>
public static string Decrypt(string CipherText, string Password = "", string Salt = "", string CryptoType = "3des", int PasswordIterations = 0, string InitialVector = "", int KeySize = 256)
{
if (string.IsNullOrEmpty(CipherText))
{
return("");
}
// INIT CRYPTOGRAPHY
CryptoInit();
// POPULATE EMPTY FIELDS WITH DEFAULT VALUES
if (Password == "")
{
Password = strDefaultKey;
}
if (Salt == "")
{
Salt = strDefaultSalt;
}
if (InitialVector == "")
{
InitialVector = strDefaultVector;
}
if (PasswordIterations == 0)
{
PasswordIterations = intDefaultIterations;
}
try
{
// DETERMINE HASH
int BlockSize = 128;
Boolean blnSetInit = false;
SymmetricAlgorithm SymmetricKey;
// SET THE CRYPTOGRAPHY METHOD
if (CryptoType.ToLower() == "aes")
{
// AES
BlockSize = 128; // MUST BE 128
if (KeySize < 128)
{
KeySize = 128;
}
if (KeySize > 256)
{
KeySize = 256;
}
// SymmetricKey = new AesCryptoServiceProvider();
SymmetricKey = new RijndaelManaged();
blnSetInit = true;
if (InitialVector.Length < (BlockSize / 8))
{
InitialVector += strDefaultVpadding.Substring(0, (BlockSize / 8) - InitialVector.Length);
}
else if (InitialVector.Length > (BlockSize / 8))
{
InitialVector = InitialVector.Substring(0, (BlockSize / 8));
}
if (Password.Length < (BlockSize / 8))
{
Password += strDefaultPadding.Substring(0, (BlockSize / 8) - Password.Length);
}
else if (Password.Length > (BlockSize / 8))
{
Password = Password.Substring(0, (BlockSize / 8));
}
}
else if (CryptoType.ToLower() == "3des")
{
// TRIPLE-DES
BlockSize = 64; // MUST BE 64
if (KeySize < 128)
{
KeySize = 128;
}
if (KeySize > 192)
{
KeySize = 192;
}
SymmetricKey = new TripleDESCryptoServiceProvider();
}
else
{
// RIJNDAEL - NOT FIPS COMPLIANT
if (BlockSize < 128)
{
BlockSize = 128;
}
if (BlockSize > 256)
{
BlockSize = 256;
}
if (KeySize < 128)
{
KeySize = 128;
}
if (KeySize > 256)
{
KeySize = 256;
}
SymmetricKey = new RijndaelManaged();
}
// SET THE INITIAL VECTOR AND CRYPTOGRAPHY PASSWORD
if (!blnSetInit)
{
if (InitialVector.Length < (BlockSize / 8))
{
InitialVector += strDefaultVpadding.Substring(0, (BlockSize / 8) - InitialVector.Length);
}
else if (InitialVector.Length > (BlockSize / 8))
{
InitialVector = InitialVector.Substring(0, (BlockSize / 8));
}
if (Password.Length < (KeySize / 8))
{
Password += strDefaultPadding.Substring(0, (KeySize / 8) - Password.Length);
}
else if (Password.Length > (KeySize / 8))
{
Password = Password.Substring(0, (KeySize / 8));
}
}
// BUILD THE DECRYPTION PARAMETERS
byte[] InitialVectorBytes = Encoding.ASCII.GetBytes(InitialVector);
byte[] CipherTextBytes = Convert.FromBase64String(CipherText);
byte[] SaltValueBytes = Encoding.ASCII.GetBytes(Salt);
Rfc2898DeriveBytes pwdGen = new Rfc2898DeriveBytes(Password, SaltValueBytes, PasswordIterations);
byte[] KeyBytes = pwdGen.GetBytes(KeySize / 8); // This will generate a 128/256 bits key
byte[] IVBytes = pwdGen.GetBytes(BlockSize / 8); // This will generate a 128/256 bits IV
SymmetricKey.Padding = PaddingMode.PKCS7;
SymmetricKey.Mode = CipherMode.CBC;
SymmetricKey.BlockSize = BlockSize;
SymmetricKey.Key = KeyBytes;
SymmetricKey.IV = IVBytes;
byte[] PlainTextBytes = new byte[CipherTextBytes.Length];
int ByteCount = 0;
// PERFORM THE DECRYPTION
using (ICryptoTransform Decryptor = SymmetricKey.CreateDecryptor(KeyBytes, InitialVectorBytes))
{
using (MemoryStream MemStream = new MemoryStream(CipherTextBytes))
{
using (CryptoStream CryptoStream = new CryptoStream(MemStream, Decryptor, CryptoStreamMode.Read))
{
ByteCount = CryptoStream.Read(PlainTextBytes, 0, PlainTextBytes.Length);
MemStream.Close();
CryptoStream.Close();
}
}
}
SymmetricKey.Clear();
return(Encoding.UTF8.GetString(PlainTextBytes, 0, ByteCount));
} catch {
return("");
}
}