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/* arcfour.c - The arcfour stream cipher
* Copyright (C) 2000, 2001, 2002 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 "arcfour.h"
static const char *selftest(void);
typedef struct {
int idx_i, idx_j;
byte sbox[256];
} ARCFOUR_context;
static void
burn_stack (int bytes)
{
char buf[64];
memset (buf, 0, sizeof buf);
bytes -= sizeof buf;
if (bytes > 0)
burn_stack (bytes);
}
static void
do_encrypt_stream( ARCFOUR_context *ctx,
byte *outbuf, const byte *inbuf, unsigned int length )
{
int t;
int i = ctx->idx_i;
int j = ctx->idx_j;
byte *sbox = ctx->sbox;
while ( length-- ) {
i = (i+1) % 256;
j = (j + sbox[i]) % 256;
t = sbox[i]; sbox[i] = sbox[j]; sbox[j] = t;
*outbuf++ = *inbuf++ ^ sbox[(sbox[i] + sbox[j]) % 256];
}
ctx->idx_i = i;
ctx->idx_j = j;
}
static void
encrypt_stream( ARCFOUR_context *ctx,
byte *outbuf, const byte *inbuf, unsigned int length )
{
do_encrypt_stream (ctx, outbuf, inbuf, length );
burn_stack (64);
}
static int
do_arcfour_setkey( ARCFOUR_context *ctx, const byte *key, unsigned int keylen )
{
static int initialized;
static const char* selftest_failed;
int i, j;
byte karr[256];
if( !initialized ) {
initialized = 1;
selftest_failed = selftest();
if( selftest_failed )
fprintf(stderr,"ARCFOUR selftest failed (%s)\n", selftest_failed );
}
if( selftest_failed )
return GCRYERR_SELFTEST;
if( keylen < 40/8 ) /* we want at least 40 bits */
return GCRYERR_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 0;
}
static int
arcfour_setkey ( ARCFOUR_context *ctx, const byte *key, unsigned int keylen )
{
int rc = do_arcfour_setkey (ctx, key, keylen );
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 const byte key_1[] =
{ 0x61, 0x8A, 0x63, 0xD2, 0xFB };
static const 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;
}
/****************
* Return some information about the algorithm. We need algo here to
* distinguish different flavors of the algorithm.
* Returns: A pointer to string describing the algorithm or NULL if
* the ALGO is invalid.
* NOTE: This is a special get_info function which is different from all
* others because arcfour is a stream cipher. We use this hack until
* we have redesign the interface.
*/
const char *
_gcry_arcfour_get_info( int algo, size_t *keylen, size_t *blocksize,
size_t *contextsize,
int (**r_setkey)( void *c, byte *key, unsigned keylen ),
void (**r_stencrypt)( void *c, byte *outbuf,
byte *inbuf, unsigned int nbytes ),
void (**r_stdecrypt)( void *c, byte *outbuf,
byte *inbuf, unsigned int nbytes )
)
{
*keylen = 128; /* arbitrary value */
*blocksize = 1;
*contextsize = sizeof(ARCFOUR_context);
*(int (**)(ARCFOUR_context*, const byte*, unsigned))r_setkey
= arcfour_setkey;
*(void (**)(ARCFOUR_context*, byte*, const byte*, unsigned))r_stencrypt
= encrypt_stream;
*(void (**)(ARCFOUR_context*, byte*, const byte*, unsigned))r_stdecrypt
= encrypt_stream;
if( algo == 301 )
return "ARCFOUR";
return NULL;
}
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