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#region Copyright
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// /************************************************************************
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// Copyright (c) 2016 Jamie Rees
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// File: StringCipher.cs
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// Created By: Jamie Rees
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//
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// Permission is hereby granted, free of charge, to any person obtaining
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// a copy of this software and associated documentation files (the
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// "Software"), to deal in the Software without restriction, including
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// without limitation the rights to use, copy, modify, merge, publish,
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// distribute, sublicense, and/or sell copies of the Software, and to
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// permit persons to whom the Software is furnished to do so, subject to
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// the following conditions:
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//
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// The above copyright notice and this permission notice shall be
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// included in all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
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// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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// ************************************************************************/
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#endregion
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using System;
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using System.IO;
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using System.Linq;
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using System.Security.Cryptography;
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using System.Text;
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namespace RequestPlex.Helpers
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{
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public class StringCipher
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{
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// This constant determines the number of iterations for the password bytes generation function.
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private const int DerivationIterations = 1000;
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// This constant is used to determine the keysize of the encryption algorithm in bits.
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// We divide this by 8 within the code below to get the equivalent number of bytes.
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private const int Keysize = 256;
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/// <summary>
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/// Decrypts the specified cipher text.
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/// </summary>
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/// <param name="cipherText">The cipher text.</param>
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/// <param name="passPhrase">The pass phrase.</param>
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/// <returns></returns>
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public static string Decrypt(string cipherText, string passPhrase)
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{
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// Get the complete stream of bytes that represent:
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// [32 bytes of Salt] + [32 bytes of IV] + [n bytes of CipherText]
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var cipherTextBytesWithSaltAndIv = Convert.FromBase64String(cipherText);
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// Get the saltbytes by extracting the first 32 bytes from the supplied cipherText bytes.
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var saltStringBytes = cipherTextBytesWithSaltAndIv.Take(Keysize / 8).ToArray();
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// Get the IV bytes by extracting the next 32 bytes from the supplied cipherText bytes.
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var ivStringBytes = cipherTextBytesWithSaltAndIv.Skip(Keysize / 8).Take(Keysize / 8).ToArray();
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// Get the actual cipher text bytes by removing the first 64 bytes from the cipherText string.
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var cipherTextBytes = cipherTextBytesWithSaltAndIv.Skip((Keysize / 8) * 2).Take(cipherTextBytesWithSaltAndIv.Length - ((Keysize / 8) * 2)).ToArray();
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using (var password = new Rfc2898DeriveBytes(passPhrase, saltStringBytes, DerivationIterations))
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{
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var keyBytes = password.GetBytes(Keysize / 8);
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using (var symmetricKey = new RijndaelManaged())
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{
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symmetricKey.BlockSize = 256;
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symmetricKey.Mode = CipherMode.CBC;
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symmetricKey.Padding = PaddingMode.PKCS7;
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using (var decryptor = symmetricKey.CreateDecryptor(keyBytes, ivStringBytes))
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{
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using (var memoryStream = new MemoryStream(cipherTextBytes))
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{
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using (var cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))
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{
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var plainTextBytes = new byte[cipherTextBytes.Length];
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var decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);
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memoryStream.Close();
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cryptoStream.Close();
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return Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);
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}
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}
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}
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}
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}
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}
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/// <summary>
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/// Encrypts the specified plain text.
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/// </summary>
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/// <param name="plainText">The plain text.</param>
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/// <param name="passPhrase">The pass phrase.</param>
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/// <returns></returns>
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public static string Encrypt(string plainText, string passPhrase)
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{
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// Salt and IV is randomly generated each time, but is preprended to encrypted cipher text
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// so that the same Salt and IV values can be used when decrypting.
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var saltStringBytes = Generate256BitsOfRandomEntropy();
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var ivStringBytes = Generate256BitsOfRandomEntropy();
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var plainTextBytes = Encoding.UTF8.GetBytes(plainText);
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using (var password = new Rfc2898DeriveBytes(passPhrase, saltStringBytes, DerivationIterations))
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{
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var keyBytes = password.GetBytes(Keysize / 8);
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using (var symmetricKey = new RijndaelManaged())
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{
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symmetricKey.BlockSize = 256;
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symmetricKey.Mode = CipherMode.CBC;
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symmetricKey.Padding = PaddingMode.PKCS7;
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using (var encryptor = symmetricKey.CreateEncryptor(keyBytes, ivStringBytes))
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{
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using (var memoryStream = new MemoryStream())
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{
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using (var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
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{
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cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);
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cryptoStream.FlushFinalBlock();
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// Create the final bytes as a concatenation of the random salt bytes, the random iv bytes and the cipher bytes.
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var cipherTextBytes = saltStringBytes;
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cipherTextBytes = cipherTextBytes.Concat(ivStringBytes).ToArray();
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cipherTextBytes = cipherTextBytes.Concat(memoryStream.ToArray()).ToArray();
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memoryStream.Close();
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cryptoStream.Close();
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return Convert.ToBase64String(cipherTextBytes);
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}
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}
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}
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}
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}
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}
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/// <summary>
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/// Generate256s the bits of random entropy.
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/// </summary>
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/// <returns></returns>
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private static byte[] Generate256BitsOfRandomEntropy()
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{
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var randomBytes = new byte[32]; // 32 Bytes will give us 256 bits.
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using (var rngCsp = new RNGCryptoServiceProvider())
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{
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// Fill the array with cryptographically secure random bytes.
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rngCsp.GetBytes(randomBytes);
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}
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return randomBytes;
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}
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}
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}
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Jamie Rees
9 years ago