Extensions/BinaryDad.Extensions/CryptoHelper.cs
2020-09-04 21:19:24 -04:00

184 lines
7.3 KiB
C#

using System;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
namespace BinaryDad.Extensions
{
/// <summary>
/// Set of cryptography helpers using AES and Rijndael cipher
/// </summary>
public static class CryptoHelper
{
// This constant is used to determine the keysize of the encryption algorithm in bits.
// We divide this by 8 within the code below to get the equivalent number of bytes.
private const int DefaultKeySize = 256;
// This constant determines the number of iterations for the password bytes generation function.
private const int DerivationIterations = 1000;
#region Encrypt
/// <summary>
/// Encrypts a string with pass key using AES (Rijndael cipher)
/// </summary>
/// <param name="plainText"></param>
/// <param name="passPhrase"></param>
/// <returns></returns>
public static string Encrypt(string plainText, string passPhrase)
{
return Encrypt(plainText, passPhrase, DefaultKeySize);
}
/// <summary>
/// Encrypts a string with pass key using AES (Rijndael cipher)
/// </summary>
/// <param name="plainText"></param>
/// <param name="passPhrase"></param>
/// <param name="keySize"></param>
/// <returns></returns>
public static string Encrypt(string plainText, string passPhrase, int keySize)
{
ValidateKeySize(keySize);
// Salt and IV is randomly generated each time, but is preprended to encrypted cipher text
// so that the same Salt and IV values can be used when decrypting.
var saltStringBytes = GenerateBitsOfRandomEntropy(keySize);
var ivStringBytes = GenerateBitsOfRandomEntropy(keySize);
var plainTextBytes = Encoding.UTF8.GetBytes(plainText);
using (var password = new Rfc2898DeriveBytes(passPhrase, saltStringBytes, DerivationIterations))
{
var keyBytes = password.GetBytes(keySize / 8);
using (var symmetricKey = new RijndaelManaged())
{
symmetricKey.BlockSize = keySize;
symmetricKey.Mode = CipherMode.CBC;
symmetricKey.Padding = PaddingMode.PKCS7;
using (var encryptor = symmetricKey.CreateEncryptor(keyBytes, ivStringBytes))
{
using (var memoryStream = new MemoryStream())
{
using (var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
{
cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);
cryptoStream.FlushFinalBlock();
// Create the final bytes as a concatenation of the random salt bytes, the random iv bytes and the cipher bytes.
var cipherTextBytes = saltStringBytes;
cipherTextBytes = cipherTextBytes.Concat(ivStringBytes).ToArray();
cipherTextBytes = cipherTextBytes.Concat(memoryStream.ToArray()).ToArray();
memoryStream.Close();
cryptoStream.Close();
return Convert.ToBase64String(cipherTextBytes);
}
}
}
}
}
}
#endregion
#region Decrypt
/// <summary>
/// Decrypts a string with pass key using AES (Rijndael cipher)
/// </summary>
/// <param name="cipherText"></param>
/// <param name="passPhrase"></param>
/// <returns></returns>
public static string Decrypt(string cipherText, string passPhrase)
{
return Decrypt(cipherText, passPhrase, DefaultKeySize);
}
/// <summary>
/// Decrypts a string with pass key using AES (Rijndael cipher)
/// </summary>
/// <param name="cipherText"></param>
/// <param name="passPhrase"></param>
/// <param name="keySize"></param>
/// <returns></returns>
public static string Decrypt(string cipherText, string passPhrase, int keySize)
{
ValidateKeySize(keySize);
// Get the complete stream of bytes that represent:
// [32 bytes of Salt] + [32 bytes of IV] + [n bytes of CipherText]
var cipherTextBytesWithSaltAndIv = Convert.FromBase64String(cipherText);
// Get the saltbytes by extracting the first 32 bytes from the supplied cipherText bytes.
var saltStringBytes = cipherTextBytesWithSaltAndIv.Take(keySize / 8).ToArray();
// Get the IV bytes by extracting the next 32 bytes from the supplied cipherText bytes.
var ivStringBytes = cipherTextBytesWithSaltAndIv.Skip(keySize / 8).Take(keySize / 8).ToArray();
// Get the actual cipher text bytes by removing the first 64 bytes from the cipherText string.
var cipherTextBytes = cipherTextBytesWithSaltAndIv.Skip((keySize / 8) * 2).Take(cipherTextBytesWithSaltAndIv.Length - ((keySize / 8) * 2)).ToArray();
using (var password = new Rfc2898DeriveBytes(passPhrase, saltStringBytes, DerivationIterations))
{
var keyBytes = password.GetBytes(keySize / 8);
using (var symmetricKey = new RijndaelManaged())
{
symmetricKey.BlockSize = keySize;
symmetricKey.Mode = CipherMode.CBC;
symmetricKey.Padding = PaddingMode.PKCS7;
using (var decryptor = symmetricKey.CreateDecryptor(keyBytes, ivStringBytes))
{
using (var memoryStream = new MemoryStream(cipherTextBytes))
{
using (var cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))
{
var plainTextBytes = new byte[cipherTextBytes.Length];
var decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);
memoryStream.Close();
cryptoStream.Close();
return Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);
}
}
}
}
}
}
#endregion
#region Private Methods
private static byte[] GenerateBitsOfRandomEntropy(int keySize)
{
var randomBytes = new byte[keySize / 8];
using (var rngCsp = new RNGCryptoServiceProvider())
{
// Fill the array with cryptographically secure random bytes.
rngCsp.GetBytes(randomBytes);
}
return randomBytes;
}
private static void ValidateKeySize(int keySize)
{
if (keySize % 8 != 0)
{
throw new ArgumentException("Key size must be a multiple of 8", nameof(keySize));
}
}
#endregion
}
}