3DES/DES encryption using the JCE - generating an acceptable key

Question

I'm working on a project that requires 3DES encryption in Java. The issue is that I've been (and will continue to be) supplied with a 128-bit hex key like "0123456789ABCDEF0123456789ABCDEF". Conversion to bytes is no issue. What is the issue, however, is that the Java Cryptographic Extensions API will choke on this key, saying it is invalid. I gather that the MSB of each byte is merely a parity bit, so the JCE expects me to remove those (or so I think). In .NET, however, I can specify the key as supplied, and it quietly handles the encryption/decryption with no complaints.

Is there any way I can generate the kind of key the JCE expects from the kind of key I'm supplied?

I've found that the JCE allows you specify an 8-byte key for DES encryption, so I tried implementing 3DES as DES EDE using half of the supplied key. However, I'm still getting inconsistent results with .NET.

Here's the Java code:

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import javax.crypto.spec.IvParameterSpec;

public class Main{
    public static void main(String[] args) throws Exception {
        byte [] plain = "I eat fish every day".getBytes("utf-8");

        byte [] keyBytes = new byte [] { (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00,
            (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00
            };

        byte [] key2Bytes = new byte [] { (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00,
            (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x0  }; // actual keys replaced with dummies.

        SecretKey keySpec = new SecretKeySpec(keyBytes, "DES");
        SecretKey keySpec2 = new SecretKeySpec(key2Bytes, "DES");

        IvParameterSpec iv = new IvParameterSpec(new byte[8]);

        Cipher e_cipher = Cipher.getInstance("DES/CBC/PKCS5Padding");
        Cipher cipher = Cipher.getInstance("DES/CBC/NoPadding");

        e_cipher.init(Cipher.ENCRYPT_MODE, keySpec, iv);
        cipher.init(Cipher.DECRYPT_MODE, keySpec2, iv);

        byte [] cipherText = e_cipher.doFinal(plain);
        cipherText = cipher.doFinal(cipherText);
        cipherText = e_cipher.doFinal(cipherText);

        System.out.println("Ciphertext: " + new sun.misc.BASE64Encoder().encode(cipherText));
    }
}

and here's the .NET code:

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace EncryptionDemo
{
    class Program
    {
    public static void Main(string[] args)
    {
        Console.WriteLine("Hello World!");

        // TODO: Implement Functionality Here
        var plainBytes = Encoding.UTF8.GetBytes("I eat fish every day");
        var keyBytes = new byte [] { 0x00, 0x00, 0x00, 0x00,
         0x00, 0x00, 0x00, 0x00,
         0x00, 0x00, 0x00, 0x00,
         0x00,  0x00, 0x00, 0x00  };

        var tripleDES = TripleDESCryptoServiceProvider.Create();
        var transform = tripleDES.CreateEncryptor(keyBytes, new byte [8]);

        var memStream = new MemoryStream();
        var cStream = new CryptoStream(memStream, transform, CryptoStreamMode.Write);

        cStream.Write(plainBytes, 0, plainBytes.Length);
        cStream.FlushFinalBlock();

        //memStream.Position = 0;
        var cipherBytes = memStream.ToArray();

        Console.WriteLine("Ciphertext: " + Convert.ToBase64String(cipherBytes));

        Console.Write("Press any key to continue . . . ");
        Console.ReadKey(true);
    }
}

Both produce different outputs (some characters in the Base64 string are the same)

Answer 1

3DES keys are 192 bits long.

How are you creating the SecretKey instance? What error message to you get?

---

The Java code in your question is using DES, not "Triple DES". The algorithm name should be "DESede/CBC/PKCS5Padding". The code in your answer probably works because you got the algorithm right, not because you switched providers. The SunJCE provider in Java 6 will accept 128-bit keys (and use keying option 2). I am not sure about older versions.