/* arcfour.c  -  The arcfour stream cipher
 *	Copyright (C) 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
 *
 * This file is part of Libgcrypt.
 *
 * Libgcrypt is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser general Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * Libgcrypt 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 *
 * For a description of the algorithm, see:
 *   Bruce Schneier: Applied Cryptography. John Wiley & Sons, 1996.
 *   ISBN 0-471-11709-9. Pages 397 ff.
 */


#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "types.h"
#include "g10lib.h"
#include "cipher.h"

static const char *selftest(void);

typedef struct {
    int idx_i, idx_j;
    byte sbox[256];
} ARCFOUR_context;

static void
do_encrypt_stream( ARCFOUR_context *ctx,
		   byte *outbuf, const byte *inbuf, unsigned int length )
{
  register int i = ctx->idx_i;
  register int j = ctx->idx_j;
  register byte *sbox = ctx->sbox;
  register int t;

  while ( length-- )
    {
      i++;
      i = i & 255; /* The and-op seems to be faster than the mod-op. */
      j += sbox[i];
      j &= 255;
      t = sbox[i]; sbox[i] = sbox[j]; sbox[j] = t;
      *outbuf++ = *inbuf++ ^ sbox[(sbox[i] + sbox[j]) & 255];
    }

  ctx->idx_i = i;
  ctx->idx_j = j;
}

static void
encrypt_stream (void *context,
                byte *outbuf, const byte *inbuf, unsigned int length)
{
  ARCFOUR_context *ctx = (ARCFOUR_context *) context;
  do_encrypt_stream (ctx, outbuf, inbuf, length );
  _gcry_burn_stack (64);
}


static gcry_err_code_t
do_arcfour_setkey (void *context, const byte *key, unsigned int keylen)
{
  static int initialized;
  static const char* selftest_failed;
  int i, j;
  byte karr[256];
  ARCFOUR_context *ctx = (ARCFOUR_context *) context;

  if (!initialized )
    {
      initialized = 1;
      selftest_failed = selftest();
      if( selftest_failed )
        log_error ("ARCFOUR selftest failed (%s)\n", selftest_failed );
    }
  if( selftest_failed )
    return GPG_ERR_SELFTEST_FAILED;

  if( keylen < 40/8 ) /* we want at least 40 bits */
    return GPG_ERR_INV_KEYLEN;

  ctx->idx_i = ctx->idx_j = 0;
  for (i=0; i < 256; i++ )
    ctx->sbox[i] = i;
  for (i=0; i < 256; i++ )
    karr[i] = key[i%keylen];
  for (i=j=0; i < 256; i++ )
    {
      int t;
      j = (j + ctx->sbox[i] + karr[i]) % 256;
      t = ctx->sbox[i];
      ctx->sbox[i] = ctx->sbox[j];
      ctx->sbox[j] = t;
    }
  memset( karr, 0, 256 );

  return GPG_ERR_NO_ERROR;
}

static gcry_err_code_t
arcfour_setkey ( void *context, const byte *key, unsigned int keylen )
{
  ARCFOUR_context *ctx = (ARCFOUR_context *) context;
  gcry_err_code_t rc = do_arcfour_setkey (ctx, key, keylen );
  _gcry_burn_stack (300);
  return rc;
}


static const char*
selftest(void)
{
  ARCFOUR_context ctx;
  byte scratch[16];

  /* Test vector from Cryptlib labeled there: "from the
     State/Commerce Department". */
  static byte key_1[] =
    { 0x61, 0x8A, 0x63, 0xD2, 0xFB };
  static byte plaintext_1[] =
    { 0xDC, 0xEE, 0x4C, 0xF9, 0x2C };
  static const byte ciphertext_1[] =
    { 0xF1, 0x38, 0x29, 0xC9, 0xDE };

  arcfour_setkey( &ctx, key_1, sizeof(key_1));
  encrypt_stream( &ctx, scratch, plaintext_1, sizeof(plaintext_1));
  if ( memcmp (scratch, ciphertext_1, sizeof (ciphertext_1)))
    return "Arcfour encryption test 1 failed.";
  arcfour_setkey( &ctx, key_1, sizeof(key_1));
  encrypt_stream(&ctx, scratch, scratch, sizeof(plaintext_1)); /* decrypt */
  if ( memcmp (scratch, plaintext_1, sizeof (plaintext_1)))
    return "Arcfour decryption test 1 failed.";
  return NULL;
}


gcry_cipher_spec_t _gcry_cipher_spec_arcfour =
  {
    "ARCFOUR", NULL, NULL, 1, 128, sizeof (ARCFOUR_context),
    arcfour_setkey, NULL, NULL, encrypt_stream, encrypt_stream,
  };
