libpurple/protocols/mxit/cipher.c

/*
 *					MXit Protocol libPurple Plugin
 *
 *					-- user password encryption --
 *
 *				Pieter Loubser	<libpurple@mxit.com>
 *
 *			(C) Copyright 2009	MXit Lifestyle (Pty) Ltd.
 *				<http://www.mxitlifestyle.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02111-1301  USA
 */

#include	<stdio.h>
#include	<unistd.h>
#include	<string.h>

#include	"purple.h"

#include	"mxit.h"
#include	"cipher.h"
#include	"aes.h"


/* password encryption */
#define		INITIAL_KEY		"6170383452343567"
#define		SECRET_HEADER	"<mxit/>"


/*------------------------------------------------------------------------
 * Pad the secret data using ISO10126 Padding.
 *
 *  @param secret	The data to pad (caller must ensure buffer has enough space for padding)
 *  @return			The total number of 128-bit blocks used
 */
static int pad_secret_data( char* secret )
{
	int		blocks	= 0;
	int		passlen;
	int		padding;

	passlen = strlen( secret );
	blocks = ( passlen / 16 ) + 1;
	padding = ( blocks * 16 ) - passlen;
	secret[passlen] = 0x50;
	secret[(blocks * 16) - 1] = padding;

	return blocks;
}


/*------------------------------------------------------------------------
 * Encrypt the user's cleartext password using the AES 128-bit (ECB)
 *  encryption algorithm.
 *
 *  @param session	The MXit session object
 *  @return			The encrypted & encoded password.  Must be g_free'd when no longer needed.
 */
char* mxit_encrypt_password( struct MXitSession* session )
{
	char		key[64];
	char		exkey[512];
	char		pass[64];
	char		encrypted[64];
	char*		base64;
	int			blocks;
	int			size;
	int			i;

	purple_debug_info( MXIT_PLUGIN_ID, "mxit_encrypt_password\n" );

	memset( encrypted, 0x00, sizeof( encrypted ) );
	memset( exkey, 0x00, sizeof( exkey ) );
	memset( pass, 0x58, sizeof( pass ) );
	pass[sizeof( pass ) - 1] = '\0';

	/* build the custom AES encryption key */
	strcpy( key, INITIAL_KEY );
	memcpy( key, session->clientkey, strlen( session->clientkey ) );
	ExpandKey( (unsigned char*) key, (unsigned char*) exkey );

	/* build the custom data to be encrypted */
	strcpy( pass, SECRET_HEADER );
	strcat( pass, session->acc->password );

	/* pad the secret data */
	blocks = pad_secret_data( pass );
	size = blocks * 16;

	/* now encrypt the password. we encrypt each block separately (ECB mode) */
	for ( i = 0; i < size; i += 16 )
		Encrypt( (unsigned char*) pass + i, (unsigned char*) exkey, (unsigned char*) encrypted + i );

	/* now base64 encode the encrypted password */
	base64 = purple_base64_encode( (unsigned char*) encrypted, size );

	return base64;
}