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crypt-rc4.c

/* 
   Unix SMB/CIFS implementation.

   a partial implementation of RC4 designed for use in the 
   SMB authentication protocol

   Copyright (C) Andrew Tridgell 1998

   $Id: crypt-rc4.c 12116 2004-09-27 23:29:22Z guy $
   
   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., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <glib.h>
#include <string.h>

#include <epan/crypt-rc4.h>

/* Perform RC4 on a block of data using specified key.  "data" is a pointer
   to the block to be processed.  Output is written to same memory as input,
   so caller may need to make a copy before calling this function, since
   the input will be overwritten.  
   
   Taken from Samba source code.  Modified to allow us to maintain state
   between calls to crypt_rc4.
*/

void crypt_rc4_init(rc4_state_struct *rc4_state, 
                const unsigned char *key, int key_len)
{
  int ind;
  unsigned char j = 0;
  unsigned char *s_box;

  memset(rc4_state, 0, sizeof(rc4_state_struct));
  s_box = rc4_state->s_box;
  
  for (ind = 0; ind < 256; ind++)
  {
    s_box[ind] = (unsigned char)ind;
  }

  for( ind = 0; ind < 256; ind++)
  {
     unsigned char tc;

     j += (s_box[ind] + key[ind%key_len]);

     tc = s_box[ind];
     s_box[ind] = s_box[j];
     s_box[j] = tc;
  }

}

void crypt_rc4(rc4_state_struct *rc4_state, unsigned char *data, int data_len)
{
  unsigned char *s_box;
  unsigned char index_i;
  unsigned char index_j;
  int ind;

  /* retrieve current state from the state struct (so we can resume where
     we left off) */
  index_i = rc4_state->index_i;
  index_j = rc4_state->index_j;
  s_box = rc4_state->s_box;

  for( ind = 0; ind < data_len; ind++)
  {
    unsigned char tc;
    unsigned char t;

    index_i++;
    index_j += s_box[index_i];

    tc = s_box[index_i];
    s_box[index_i] = s_box[index_j];
    s_box[index_j] = tc;

    t = s_box[index_i] + s_box[index_j];
    data[ind] = data[ind] ^ s_box[t];
  }

  /* Store the updated state */
  rc4_state->index_i = index_i;
  rc4_state->index_j = index_j;
}

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