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1/* arcfour.c - The arcfour stream cipher
2 *Copyright (C) 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
3 *
4 * This file is part of Libgcrypt.
5 *
6 * Libgcrypt is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU Lesser general Public License as
8 * published by the Free Software Foundation; either version 2.1 of
9 * the License, or (at your option) any later version.
10 *
11 * Libgcrypt is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with this program; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
19 *
20 * For a description of the algorithm, see:
21 * Bruce Schneier: Applied Cryptography. John Wiley & Sons, 1996.
22 * ISBN 0-471-11709-9. Pages 397 ff.
23 */
24
25
26#include <config.h>
27#include <stdio.h>
28#include <stdlib.h>
29#include <string.h>
30#include "types.h"
31#include "g10lib.h"
32#include "cipher.h"
33
34static const char *selftest(void);
35
36typedef struct {
37 int idx_i, idx_j;
38 byte sbox[256];
39} ARCFOUR_context;
40
41static void
42do_encrypt_stream( ARCFOUR_context *ctx,
43 byte *outbuf, const byte *inbuf, unsigned int length )
44{
45 register int i = ctx->idx_i;
46 register int j = ctx->idx_j;
47 register byte *sbox = ctx->sbox;
48 register int t;
49
50 while ( length-- )
51 {
52 i++;
53 i = i & 255; /* The and-op seems to be faster than the mod-op. */
54 j += sbox[i];
55 j &= 255;
56 t = sbox[i]; sbox[i] = sbox[j]; sbox[j] = t;
57 *outbuf++ = *inbuf++ ^ sbox[(sbox[i] + sbox[j]) & 255];
58 }
59
60 ctx->idx_i = i;
61 ctx->idx_j = j;
62}
63
64static void
65encrypt_stream (void *context,
66 byte *outbuf, const byte *inbuf, unsigned int length)
67{
68 ARCFOUR_context *ctx = (ARCFOUR_context *) context;
69 do_encrypt_stream (ctx, outbuf, inbuf, length );
70 _gcry_burn_stack (64);
71}
72
73
74static gcry_err_code_t
75do_arcfour_setkey (void *context, const byte *key, unsigned int keylen)
76{
77 static int initialized;
78 static const char* selftest_failed;
79 int i, j;
80 byte karr[256];
81 ARCFOUR_context *ctx = (ARCFOUR_context *) context;
82
83 if (!initialized )
84 {
85 initialized = 1;
86 selftest_failed = selftest();
87 if( selftest_failed )
88 log_error ("ARCFOUR selftest failed (%s)\n", selftest_failed );
89 }
90 if( selftest_failed )
91 return GPG_ERR_SELFTEST_FAILED;
92
93 if( keylen < 40/8 ) /* we want at least 40 bits */
94 return GPG_ERR_INV_KEYLEN;
95
96 ctx->idx_i = ctx->idx_j = 0;
97 for (i=0; i < 256; i++ )
98 ctx->sbox[i] = i;
99 for (i=0; i < 256; i++ )
100 karr[i] = key[i%keylen];
101 for (i=j=0; i < 256; i++ )
102 {
103 int t;
104 j = (j + ctx->sbox[i] + karr[i]) % 256;
105 t = ctx->sbox[i];
106 ctx->sbox[i] = ctx->sbox[j];
107 ctx->sbox[j] = t;
108 }
109 memset( karr, 0, 256 );
110
111 return GPG_ERR_NO_ERROR;
112}
113
114static gcry_err_code_t
115arcfour_setkey ( void *context, const byte *key, unsigned int keylen )
116{
117 ARCFOUR_context *ctx = (ARCFOUR_context *) context;
118 gcry_err_code_t rc = do_arcfour_setkey (ctx, key, keylen );
119 _gcry_burn_stack (300);
120 return rc;
121}
122
123
124static const char*
125selftest(void)
126{
127 ARCFOUR_context ctx;
128 byte scratch[16];
129
130 /* Test vector from Cryptlib labeled there: "from the
131 State/Commerce Department". */
132 static byte key_1[] =
133 { 0x61, 0x8A, 0x63, 0xD2, 0xFB };
134 static byte plaintext_1[] =
135 { 0xDC, 0xEE, 0x4C, 0xF9, 0x2C };
136 static const byte ciphertext_1[] =
137 { 0xF1, 0x38, 0x29, 0xC9, 0xDE };
138
139 arcfour_setkey( &ctx, key_1, sizeof(key_1));
140 encrypt_stream( &ctx, scratch, plaintext_1, sizeof(plaintext_1));
141 if ( memcmp (scratch, ciphertext_1, sizeof (ciphertext_1)))
142 return "Arcfour encryption test 1 failed.";
143 arcfour_setkey( &ctx, key_1, sizeof(key_1));
144 encrypt_stream(&ctx, scratch, scratch, sizeof(plaintext_1)); /* decrypt */
145 if ( memcmp (scratch, plaintext_1, sizeof (plaintext_1)))
146 return "Arcfour decryption test 1 failed.";
147 return NULL;
148}
149
150
151gcry_cipher_spec_t _gcry_cipher_spec_arcfour =
152 {
153 "ARCFOUR", NULL, NULL, 1, 128, sizeof (ARCFOUR_context),
154 arcfour_setkey, NULL, NULL, encrypt_stream, encrypt_stream,
155 };
156