How to generate Rijndael KEY and IV using a passphrase?
This is plug and play code that I found on internet. It just works:
using System.IO;
using System.Security.Cryptography;
private static readonly byte[] SALT = new byte[] { 0x26, 0xdc, 0xff, 0x00, 0xad, 0xed, 0x7a, 0xee, 0xc5, 0xfe, 0x07, 0xaf, 0x4d, 0x08, 0x22, 0x3c };
public static byte[] Encrypt(byte[] plain, string password)
{
MemoryStream memoryStream;
CryptoStream cryptoStream;
Rijndael rijndael = Rijndael.Create();
Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(password, SALT);
rijndael.Key = pdb.GetBytes(32);
rijndael.IV = pdb.GetBytes(16);
memoryStream = new MemoryStream();
cryptoStream = new CryptoStream(memoryStream, rijndael.CreateEncryptor(), CryptoStreamMode.Write);
cryptoStream.Write(plain, 0, plain.Length);
cryptoStream.Close();
return memoryStream.ToArray();
}
public static byte[] Decrypt(byte[] cipher, string password)
{
MemoryStream memoryStream;
CryptoStream cryptoStream;
Rijndael rijndael = Rijndael.Create();
Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(password, SALT);
rijndael.Key = pdb.GetBytes(32);
rijndael.IV = pdb.GetBytes(16);
memoryStream = new MemoryStream();
cryptoStream = new CryptoStream(memoryStream, rijndael.CreateDecryptor(), CryptoStreamMode.Write);
cryptoStream.Write(cipher, 0, cipher.Length);
cryptoStream.Close();
return memoryStream.ToArray();
}
I think you are looking for password-based key derivation. There is Rfc2898DeriveBytes
class that implements it.
Rfc2898DeriveBytes
takes a password, a salt, and an iteration count, and then generates keys through calls to the GetBytes
method.
RFC 2898 includes methods for creating a key and initialization vector (IV) from a password and salt. You can use PBKDF2, a password-based key derivation function, to derive keys using a pseudo-random function that allows keys of virtually unlimited length to be generated. The Rfc2898DeriveBytes class can be used to produce a derived key from a base key and other parameters. In a password-based key derivation function, the base key is a password and the other parameters are a salt value and an iteration count.
For more information about PBKDF2, see RFC 2898, "PKCS #5: Password-Based Cryptography Specification Version 2.0,".
Example:
public static byte[] CreateKey(string password)
{
var salt = new byte[] { 1, 2, 23, 234, 37, 48, 134, 63, 248, 4 };
const int Iterations = 9872;
using (var rfc2898DeriveBytes = new Rfc2898DeriveBytes(password, salt, Iterations))
return rfc2898DeriveBytes.GetBytes(32);
}
You can use DeriveBytes
in any symmetric algorithm, not just Rijndael
.
Example:
public static SymmetricAlgorithm InitSymmetric(SymmetricAlgorithm algorithm, string password, int keyBitLength)
{
var salt = new byte[] { 1, 2, 23, 234, 37, 48, 134, 63, 248, 4 };
const int Iterations = 234;
using (var rfc2898DeriveBytes = new Rfc2898DeriveBytes(password, salt, Iterations))
{
if (!algorithm.ValidKeySize(keyBitLength))
throw new InvalidOperationException("Invalid size key");
algorithm.Key = rfc2898DeriveBytes.GetBytes(keyBitLength / 8);
algorithm.IV = rfc2898DeriveBytes.GetBytes(algorithm.BlockSize / 8);
return algorithm;
}
}
private static byte[] Transform(byte[] bytes, Func<ICryptoTransform> selectCryptoTransform)
{
using (var memoryStream = new MemoryStream())
{
using (var cryptoStream = new CryptoStream(memoryStream, selectCryptoTransform(), CryptoStreamMode.Write))
cryptoStream.Write(bytes, 0, bytes.Length);
return memoryStream.ToArray();
}
}
Usage:
public static void Main()
{
using (var rijndael = InitSymmetric(Rijndael.Create(), "TestPassword", 256))
{
var text = "Some text to encrypt";
var bytes = Encoding.UTF8.GetBytes(text);
var encryptedBytes = Transform(bytes, rijndael.CreateEncryptor);
var decryptedBytes = Transform(encryptedBytes, rijndael.CreateDecryptor);
var decryptedText = Encoding.UTF8.GetString(decryptedBytes);
Debug.Assert(text == decryptedText);
}
}
Make sure you change salt
and iterations
parameters.