///////////////////////////////////////////////////////////////////////////////
// SAMPLE: Symmetric key encryption and decryption using Rijndael algorithm.
// 
// To run this sample, create a new Visual C# project using the Console
// Application template and replace the contents of the Class1.cs file with
// the code below.
//
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND, 
// EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED 
// WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A PARTICULAR PURPOSE.
// 
// Copyright (C) 2002 Obviex(TM). All rights reserved.
//
// http://www.obviex.com/samples/Encryption.aspx
// 
using System;
using System.IO;
using System.Text;
using System.Security.Cryptography;

namespace RijndaelEncryptDecrypt
{
    /// <summary>
    /// This class uses a symmetric key algorithm (Rijndael/AES) to encrypt and 
    /// decrypt data. As long as encryption and decryption routines use the same
    /// parameters to generate the keys, the keys are guaranteed to be the same.
    /// The class uses static functions with duplicate code to make it easier to
    /// demonstrate encryption and decryption logic. In a real-life application, 
    /// this may not be the most efficient way of handling encryption, so - as
    /// soon as you feel comfortable with it - you may want to redesign this class.
    /// </summary>
    public class Rijndael
    {
        /// <summary>
        /// Encrypts specified plaintext using Rijndael symmetric key algorithm
        /// and returns a base64-encoded result.
        /// </summary>
        /// <param name="plainText">
        /// Plaintext value to be encrypted.
        /// </param>
        /// <param name="passPhrase">
        /// Passphrase from which a pseudo-random password will be derived. The
        /// derived password will be used to generate the encryption key.
        /// Passphrase can be any string. In this example we assume that this
        /// passphrase is an ASCII string.
        /// </param>
        /// <param name="saltValue">
        /// Salt value used along with passphrase to generate password. Salt can
        /// be any string. In this example we assume that salt is an ASCII string.
        /// </param>
        /// <param name="hashAlgorithm">
        /// Hash algorithm used to generate password. Allowed values are: "MD5" and
        /// "SHA1". SHA1 hashes are a bit slower, but more secure than MD5 hashes.
        /// </param>
        /// <param name="passwordIterations">
        /// Number of iterations used to generate password. One or two iterations
        /// should be enough.
        /// </param>
        /// <param name="initVector">
        /// Initialization vector (or IV). This value is required to encrypt the
        /// first block of plaintext data. For RijndaelManaged class IV must be 
        /// exactly 16 ASCII characters long.
        /// </param>
        /// <param name="keySize">
        /// Size of encryption key in bits. Allowed values are: 128, 192, and 256. 
        /// Longer keys are more secure than shorter keys.
        /// </param>
        /// <returns>
        /// Encrypted value formatted as a base64-encoded string.
        /// </returns>
        public static string Encrypt(string plainText,
                                     string passPhrase,
                                     string saltValue,
                                     string hashAlgorithm,
                                     int passwordIterations,
                                     string initVector,
                                     int keySize)
        {
            // Convert strings 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 plaintext into a byte array.
            // Let us assume that plaintext contains UTF8-encoded characters.
            byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);

            // 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,
                                                            saltValueBytes,
                                                            hashAlgorithm,
                                                            passwordIterations);

            // 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 encryptor from the existing key bytes and initialization 
            // vector. Key size will be defined based on the number of the key 
            // bytes.
            ICryptoTransform encryptor = symmetricKey.CreateEncryptor(
                                                             keyBytes,
                                                             initVectorBytes);

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

            // Define cryptographic stream (always use Write mode for encryption).
            CryptoStream cryptoStream = new CryptoStream(memoryStream,
                                                         encryptor,
                                                         CryptoStreamMode.Write);
            // Start encrypting.
            cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);

            // Finish encrypting.
            cryptoStream.FlushFinalBlock();

            // Convert our encrypted data from a memory stream into a byte array.
            byte[] cipherTextBytes = memoryStream.ToArray();

            // Close both streams.
            memoryStream.Close();
            cryptoStream.Close();

            // Convert encrypted data into a base64-encoded string.
            string cipherText = Convert.ToBase64String(cipherTextBytes);

            // Return encrypted string.
            return cipherText;
        }

        /// <summary>
        /// Decrypts specified ciphertext using Rijndael symmetric key algorithm.
        /// </summary>
        /// <param name="cipherText">
        /// Base64-formatted ciphertext value.
        /// </param>
        /// <param name="passPhrase">
        /// Passphrase from which a pseudo-random password will be derived. The
        /// derived password will be used to generate the encryption key.
        /// Passphrase can be any string. In this example we assume that this
        /// passphrase is an ASCII string.
        /// </param>
        /// <param name="saltValue">
        /// Salt value used along with passphrase to generate password. Salt can
        /// be any string. In this example we assume that salt is an ASCII string.
        /// </param>
        /// <param name="hashAlgorithm">
        /// Hash algorithm used to generate password. Allowed values are: "MD5" and
        /// "SHA1". SHA1 hashes are a bit slower, but more secure than MD5 hashes.
        /// </param>
        /// <param name="passwordIterations">
        /// Number of iterations used to generate password. One or two iterations
        /// should be enough.
        /// </param>
        /// <param name="initVector">
        /// Initialization vector (or IV). This value is required to encrypt the
        /// first block of plaintext data. For RijndaelManaged class IV must be
        /// exactly 16 ASCII characters long.
        /// </param>
        /// <param name="keySize">
        /// Size of encryption key in bits. Allowed values are: 128, 192, and 256.
        /// Longer keys are more secure than shorter keys.
        /// </param>
        /// <returns>
        /// Decrypted string value.
        /// </returns>
        /// <remarks>
        /// Most of the logic in this function is similar to the Encrypt
        /// logic. In order for decryption to work, all parameters of this function
        /// - except cipherText value - must match the corresponding parameters of
        /// the Encrypt function which was called to generate the
        /// ciphertext.
        /// </remarks>
        public static 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(
                                                            passPhrase,
                                                            saltValueBytes,
                                                            hashAlgorithm,
                                                            passwordIterations);

            // 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(
                                                             keyBytes,
                                                             initVectorBytes);

            // 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,
                                                          decryptor,
                                                          CryptoStreamMode.Read);

            // 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.
            memoryStream.Close();
            cryptoStream.Close();

            // 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;
        }
    }
}