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Posted 11 May 2010

Simple Decryption in C#

, 11 May 2010
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string passPhrase = "Pas5pr@se"; // can be any string string saltValue = "s@1tValue"; // can be any string string hashAlgorithm = "SHA1"; // can be "MD5" int passwordIterations = 2; // can be any number string...
string passPhrase = "Pas5pr@se";        // can be any string
        string saltValue = "s@1tValue";        // 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

public string Decrypt(string cipherText,
                                     string passPhrase,
                                     string saltValue,
                                     string hashAlgorithm,
                                     int passwordIterations,
                                     string initVector,
                                     int keySize)
            // 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(
            // 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,
            // 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,
            // Return decrypted string.   
            return plainText;


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Peace ON
Software Developer (Senior)
India India
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