eric’s extremeboredom

So I’ve decided to start blogging about Meshwork, since thats what I spend most of my time on anyway. I’ve created a seporate category for Meshwork Development posts, however I’ll mark all posts under “Software Development” as well.

I finally got around to get socket< -->socket encryption up and running in Meshwork. It’s currently 192-bit TripleDES encryption using the Diffle-Hellman key exchange protocol.

I’m using the Diffle-Hellman class from Mentalis.org, which is incredibly easy to use and under an extremely generous license.

I don’t like working with streams, so I hacked together a quick wrapper to make everything much simplier. Below is a modified version of the DH test app from mentalis I wrote to figure out how to get DH and TripleDESCryptoServiceProvider working together:

using System;
using System.IO;
using Org.Mentalis.Security.Cryptography;
using System.Security;
using System.Security.Cryptography;

internal class TestApp {
	public static void Main(string[] args) {

		/* Do a simple DH key exchange, obviously this will usually happen
		 * over something like a socket */

		DiffieHellman dh1 = new DiffieHellmanManaged();
	 	DiffieHellman dh2 = new DiffieHellmanManaged();

		/* This is the information that we trade with the remote client */
		byte[] ke1 = dh1.CreateKeyExchange();
		byte[] ke2 = dh2.CreateKeyExchange();

		byte[] dh2k = dh2.DecryptKeyExchange(ke1);
		byte[] dh1k = dh1.DecryptKeyExchange(ke2);

		/* Print both keys to demonstrate that they are the same */
		Console.WriteLine("Computed secret of instance 1:");
		PrintBytes(dh1k);
		Console.WriteLine("");
		Console.WriteLine("Computed secret of instance 2:");
		PrintBytes(dh2k);

		TripleDESCryptoServiceProvider d = new TripleDESCryptoServiceProvider();

		/* DH gives us 128 bytes. We want a 192-bit key so we
		 * use a key of 24 bytes and an iv of 8 bytes (24*8=192) */

		byte[] b1 = new byte[24];
		byte[] b2 = new byte[8];
		Array.Copy(dh2k,0,b1,0,24);
		Array.Copy(dh2k,8,b2,0,8);

		/* Encrypt and decrypt a string... */
		byte[] myText = System.Text.Encoding.UTF8.GetBytes("TEST? woot woot!");
		byte[] ee = Encrypt(d.CreateEncryptor(b1,b2),myText);
		byte[] dd = Decrypt(d.CreateDecryptor(b1,b2),ee,myText.Length);

		/* Demonstrate that we got the correct result */
		Console.WriteLine("");
		PrintBytes(myText);
		PrintBytes(dd);

		Console.WriteLine("");
		Console.WriteLine("Press ENTER to continue...");
		Console.ReadLine();
	}

	private static byte[] Encrypt (ICryptoTransform theTransform , byte[] theBuffer) {
		MemoryStream memStream = new MemoryStream();
		CryptoStream encryptStream = new CryptoStream(memStream,theTransform, CryptoStreamMode.Write);
		encryptStream.Write(theBuffer,0,theBuffer.Length);
		encryptStream.FlushFinalBlock();
		memStream.Position = 0;
		return memStream.ToArray();
	}
	private static byte[] Decrypt(ICryptoTransform theTransform , byte[] theBuffer, int length) {
		MemoryStream memStream = new MemoryStream();
		memStream.Write(theBuffer,0,theBuffer.Length);
		memStream.Position = 0;
		CryptoStream decryptStream  = new CryptoStream(memStream,theTransform, CryptoStreamMode.Read);
		byte[] newBuff = new byte[length];
		decryptStream.Read(newBuff,0,length);

		decryptStream.Close();
		memStream.Close();
		return newBuff;
	}

	private static void PrintBytes(byte[] bytes) {
		if (bytes == null)
			return;
		for(int i = 0; i < bytes.Length; i++) {
			Console.Write(bytes[i].ToString("X2"));
		}
		Console.WriteLine();
	}
}