//*************************************************************************
//
// DeriveKeyM
// Derive key material using PKCS #1 v1.5 algorithm with MD5 hash
//
// Copyright (C) 2005.  Michel I. Gallant
//
//*************************************************************************
//
//  DeriveKeyM.cs
//
//  Derive a key from a pswd and Salt using MD5 and PKCS #5 v1.5 approach
//   see also:   http://www.openssl.org/docs/crypto/EVP_BytesToKey.html
//   see also:   http://java.sun.com/j2se/1.5.0/docs/guide/security/jce/JCERefGuide.html#PBE
//
//**************************************************************************

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

public class DeriveKeyM{

 public static void Main(String[] args)   {
	if(args.Length < 4) {
	 Console.WriteLine("Usage:   DeriveKey  <pswd>   <hexencoded Salt>   <iteration count>  <M iteration>") ;
	 return;
	}

	int HASHLENGTH = 16;	//MD5 bytes
	String chars = args[0];
	String hexstr = args[1] ;
	int count = Int32.Parse(args[2]);
	int miter  = Int32.Parse(args[3]) ;

	byte[] keymaterial = new byte[HASHLENGTH*miter] ;     //to store contatenated Mi hashed results

	// --- get secret password bytes ----
	byte[] psbytes;
        	UTF8Encoding utf8 = new UTF8Encoding();
	psbytes = utf8.GetBytes(chars);

	// --- decode hex-encoded salt string into bytes ---
	byte[] salt = new byte[hexstr.Length/2]; 
	for (int i=0; i <salt.Length; i++)    // two alternate methods
	   salt[i] = Convert.ToByte(hexstr.Substring (i*2, 2), 16); 


	// --- contatenate salt and pswd bytes into fixed data array ---
	byte[] data00 = new byte[psbytes.Length + salt.Length] ;
	Array.Copy(psbytes, data00, psbytes.Length);		//copy the pswd bytes
	Array.Copy(salt, 0, data00, psbytes.Length, salt.Length) ;	//concatenate the salt bytes
	Console.WriteLine("\nContatenated pswd || salt");
	showBytes(data00) ;


	Console.WriteLine("\nComputing hash {0} times over {1} algorithm iterations", count, miter) ;

	// ---- do multi-hashing and contatenate results  D1, D2 ...  into keymaterial bytes ----
	MD5 md5 = new MD5CryptoServiceProvider();
	byte[] result = null;
	byte[] hashtarget = new byte[HASHLENGTH + data00.Length];   //fixed length initial hashtarget

	for(int j=0; j<miter; j++)
	{
	// ----  Now hash consecutively for count times ------
	if(j == 0)
		result = data00;   	//initialize 
	else {
		Array.Copy(result, hashtarget, result.Length);
		Array.Copy(data00, 0, hashtarget, result.Length, data00.Length) ;
		result = hashtarget;
			//Console.WriteLine("Updated new initial hash target:") ;
			//showBytes(result) ;
	}

	for(int i=0; i<count; i++)
		result = md5.ComputeHash(result);

	 Console.WriteLine("\nD_{0}", (j+1));
	 showBytes(result);
	 Array.Copy(result, 0, keymaterial, j*HASHLENGTH, result.Length);  //contatenate to keymaterial
	}

	Console.WriteLine("\nContatenated key data: ");
	showBytes(keymaterial);
 }


  private static void showBytes(byte[] data){
  for(int i=1; i<=data.Length; i++){	
	Console.Write("{0:X2}", data[i-1]) ;
	}
  Console.WriteLine();
  }

}