Saturday, 8 December 2012

C# decryption password


    public string Decrypt(string cipherText,string salt)
        string passPhrase = "Pas5pr@se";        // can be any string
        string saltValue = salt;        // can be any string
        string hashAlgorithm = "SHA1";             // can be "MD5"
        int passwordIterations = 2;                  // can be any number
        string initVector = "@1B2c3D4e5F6g7H8"; // must be 16 bytes
        int keySize = 256;                // can be 192 or 128
        cipherText = cipherText.Replace(" ", "+");

        // Convert strings defining encryption key characteristics into byte
        // arrays. Let us assume that strings only contain ASCII codes.
        // If strings include Unicode characters, use Unicode, UTF7, or UTF8
        // encoding.
        byte[] initVectorBytes = Encoding.ASCII.GetBytes(initVector);
        byte[] saltValueBytes = Encoding.ASCII.GetBytes(saltValue);

        // Convert our ciphertext into a byte array.
        byte[] cipherTextBytes = Convert.FromBase64String(cipherText);

        // First, we must create a password, from which the key will be
        // derived. This password will be generated from the specified
        // passphrase and salt value. The password will be created using
        // the specified hash algorithm. Password creation can be done in
        // several iterations.
        PasswordDeriveBytes password = new PasswordDeriveBytes(passPhrase,

        // Use the password to generate pseudo-random bytes for the encryption
        // key. Specify the size of the key in bytes (instead of bits).
        byte[] keyBytes = password.GetBytes(keySize / 8);

        // Create uninitialized Rijndael encryption object.
        RijndaelManaged symmetricKey = new RijndaelManaged();

        // It is reasonable to set encryption mode to Cipher Block Chaining
        // (CBC). Use default options for other symmetric key parameters.
        symmetricKey.Mode = CipherMode.CBC;

        // Generate decryptor from the existing key bytes and initialization
        // vector. Key size will be defined based on the number of the key
        // bytes.
        ICryptoTransform decryptor = symmetricKey.CreateDecryptor(

        // Define memory stream which will be used to hold encrypted data.
        MemoryStream memoryStream = new MemoryStream(cipherTextBytes);

        // Define cryptographic stream (always use Read mode for encryption).
        CryptoStream cryptoStream = new CryptoStream(memoryStream,

        // Since at this point we don't know what the size of decrypted data
        // will be, allocate the buffer long enough to hold ciphertext;
        // plaintext is never longer than ciphertext.
        byte[] plainTextBytes = new byte[cipherTextBytes.Length];
        // Start decrypting.
        int decryptedByteCount = cryptoStream.Read(plainTextBytes,0,plainTextBytes.Length);

        // Close both streams.

        // Convert decrypted data into a string.
        // Let us assume that the original plaintext string was UTF8-encoded.
        string plainText = Encoding.UTF8.GetString(plainTextBytes,0,decryptedByteCount);

        // Return decrypted string.  
        return plainText;

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