Migrating C# .Net encrypt/decrypt algorithm to Ruby

Question

I have to encrypt/decrypt data from a .Net based web service that is using the following code (based on Rijndael algorithm):

/**
 * Cifra una cadena texto con el algoritmo de Rijndael
 *
 * @param   plainMessage    mensaje plano (sin cifrar)
 * @param   p_strSpecialKey key especial
 * @return  string          texto cifrado en hexadecimal
 */
public static string AES_encryptString(String plainMessage, string p_strSpecialKey) {
  string strTxtEncrypt = "";

  // Crear una instancia del algoritmo de Rijndael
  try {
    Rijndael RijndaelAlg = Rijndael.Create();
    RijndaelAlg.KeySize = 128;
    RijndaelAlg.Mode = CipherMode.ECB;
    RijndaelAlg.Padding = PaddingMode.Zeros;

    byte[] Key = Encoding.UTF8.GetBytes(p_strSpecialKey);
    byte[] IV = RijndaelAlg.IV;

    int keySize = 32;
    Array.Resize(ref Key, keySize);

    // Establecer un flujo en memoria para el cifrado
    MemoryStream memoryStream = new MemoryStream();

    // Crear un flujo de cifrado basado en el flujo de los datos
    CryptoStream cryptoStream = new CryptoStream(memoryStream,
    RijndaelAlg.CreateEncryptor(Key, IV),
    CryptoStreamMode.Write);

    // Obtener la representación en bytes de la información a cifrar
    byte[] plainMessageBytes = Encoding.UTF8.GetBytes(plainMessage);

    // Cifrar los datos enviándolos al flujo de cifrado
    cryptoStream.Write(plainMessageBytes, 0, plainMessageBytes.Length);
    cryptoStream.FlushFinalBlock();

    // Obtener los datos datos cifrados como un arreglo de bytes
    byte[] cipherMessageBytes = memoryStream.ToArray();

    // Cerrar los flujos utilizados
    memoryStream.Close();
    cryptoStream.Close();

    strTxtEncrypt = ByteToHex(cipherMessageBytes);
  } catch (Exception ex) {
    AddToFile("Error al encriptar el valor: " + plainMessage + " con la clave especial: " + p_strSpecialKey + " " + ex.ToString());
  }

  return strTxtEncrypt;
}

/**
 * Descifra una cadena texto con el algoritmo de Rijndael
 *
 * @param   encryptedMessage    mensaje cifrado en hexadecimal
 * @param   p_strSpecialKey key especial
 * @return  string              texto descifrado (plano)
 */
public static string AES_decryptString(String encryptedMessage, string p_strSpecialKey) {
  string strDecrypt = "";

  // Crear una instancia del algoritmo de Rijndael
  try {
    Rijndael RijndaelAlg = Rijndael.Create();
    RijndaelAlg.KeySize = 128;
    RijndaelAlg.Mode = CipherMode.ECB;
    RijndaelAlg.Padding = PaddingMode.Zeros;

    byte[] Key = Encoding.UTF8.GetBytes(p_strSpecialKey);
    byte[] IV = RijndaelAlg.IV;

    int keySize = 32;
    Array.Resize(ref Key, keySize);

    // Obtener la representación en bytes del texto cifrado
    byte[] cipherTextBytes = HexToByteArray(encryptedMessage);

    // Crear un arreglo de bytes para almacenar los datos descifrados
    byte[] plainTextBytes = new byte[cipherTextBytes.Length];

    // Crear un flujo en memoria con la representación de bytes de la información cifrada
    MemoryStream memoryStream = new MemoryStream(cipherTextBytes);

    // Crear un flujo de descifrado basado en el flujo de los datos
    CryptoStream cryptoStream = new CryptoStream(memoryStream,
    RijndaelAlg.CreateDecryptor(Key, IV),
    CryptoStreamMode.Read);

    // Obtener los datos descifrados obteniéndolos del flujo de descifrado
    int decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);

    // Cerrar los flujos utilizados
    memoryStream.Close();
    cryptoStream.Close();

    // Retornar la representación de texto de los datos descifrados
    strDecrypt = Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount).Replace("\0", "");
  } catch (Exception ex) {
    AddToFile("Error al desencriptar el valor: " + encryptedMessage + " con la clave especial: " + p_strSpecialKey + " " + ex.ToString());
  }

  return strDecrypt;
}

I have investigated the way to do the same on Ruby and I found this answer (How to decode Rijndael in ruby (encoded in VB.net)) but it doesn't works for me. Also, I'm not sure of what value i have to use for the iv. The web service brings me a Token that i have to use as the key (100% sure about that), but, actually don't know what i'm missing up.

The code I'm using for encrypt is:

# /lib/crypt.rb
module Crypt
  ...
  def Crypt.encrypt(data, key, iv, cipher_type)
    aes = OpenSSL::Cipher::Cipher.new(cipher_type)
    aes.encrypt
    aes.key = key
    aes.iv = iv
    aes.update(data) + aes.final
  end
end

# ../ws.rb
...
token = "8c5d0e6b93cf5d38d7a076b2db35ee6d" #this is a one of the tokens i received
iv = token
Crypt.encrypt(a_serialized_json,token,iv,"AES-128-CBC")

The encrypted serialized json data that I have to send must be like a hexdigest string like this "f0997ddbb17b08913e00b6fb2541312c1cfdda85e555451a1832df076a5d4a5f7d81d8db92715eade144e9696dfbe9eea573baa8ea90cdbe5baadf32fdeb6db8c9ab6743f8eeeb508921999d7513fad3". But the method described on the link generates a encrypted string like this ""^w\x9A\x90B\xDC\f\x16\xB8\xBDt\xFBo\xD7r\x97"".

Any idea of what I'm doing wrong or what I'm missing?

UPDATE: I figured out that the string output I'm getting is a byte array, and i have to convert this byte array to an hex string. I'm using the following aproach (https://github.com/atomicobject/hex_string/blob/master/lib/hex_string.rb). But, still not sure if Cypher is properly configured to acts as the C# code.

Answer 1

Finally, I found a library that exactly match the C# code and is ruby-mcrypt (https://github.com/kingpong/ruby-mcrypt). And the encryption/decryption code i used is this:

require 'mcrypt'

module Crypt
  def Crypt.m_encrypt(data, key)
    crypto = Mcrypt.new(:rijndael_128, :ecb, key, nil, :zeros)
    encrypted_data = crypto.encrypt(data)
    encrypted_data
  end

  def Crypt.m_decrypt(data, key)
    crypto = Mcrypt.new(:rijndael_128, :ecb, key, nil, :zeros)
    crypto.decrypt(data)
  end
end

IMPORTANT: This C# Rjandael library doesn't uses the IV, for that reason i'm giving nil parameter as IV to Mcrypt.

This is only the encryption/decryption section, i'm also converting string to hexa format. Hope it can help somebody else!