2 * The ARC4 stream cipher.
4 * Copyright (c) 2009 Joshua Oreman <oremanj@rwcr.net>.
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License as
8 * published by the Free Software Foundation; either version 2 of the
9 * License, or any later version.
11 * This program is distributed in the hope that it will be useful, but
12 * WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
22 FILE_LICENCE ( GPL2_OR_LATER
);
24 #include <ipxe/crypto.h>
25 #include <ipxe/arc4.h>
27 #define SWAP( ary, i, j ) \
28 ({ u8 temp = ary[i]; ary[i] = ary[j]; ary[j] = temp; })
33 * @v ctxv ARC4 encryption context
35 * @v keylen Length of key
37 * If an initialisation vector is to be used, it should be prepended
38 * to the key; ARC4 does not implement the @c setiv function because
39 * there is no standard length for an initialisation vector in the
42 static int arc4_setkey ( void *ctxv
, const void *keyv
, size_t keylen
)
44 struct arc4_ctx
*ctx
= ctxv
;
49 for ( i
= 0; i
< 256; i
++ ) {
53 for ( i
= j
= 0; i
< 256; i
++ ) {
54 j
= ( j
+ S
[i
] + key
[i
% keylen
] ) & 0xff;
63 * Perform ARC4 encryption or decryption
65 * @v ctxv ARC4 encryption context
66 * @v srcv Data to encrypt or decrypt
67 * @v dstv Location to store encrypted or decrypted data
68 * @v len Length of data to operate on
70 * ARC4 is a stream cipher that works by generating a stream of PRNG
71 * data based on the key, and XOR'ing it with the data to be
72 * encrypted. Since XOR is symmetric, encryption and decryption in
73 * ARC4 are the same operation.
75 * If you pass a @c NULL source or destination pointer, @a len
76 * keystream bytes will be consumed without encrypting any data.
78 static void arc4_xor ( void *ctxv
, const void *srcv
, void *dstv
,
81 struct arc4_ctx
*ctx
= ctxv
;
85 int i
= ctx
->i
, j
= ctx
->j
;
89 j
= ( j
+ S
[i
] ) & 0xff;
92 *dst
++ = *src
++ ^ S
[(S
[i
] + S
[j
]) & 0xff];
99 static void arc4_setiv ( void *ctx __unused
, const void *iv __unused
)
101 /* ARC4 does not use a fixed-length IV */
106 * Perform ARC4 encryption or decryption, skipping initial keystream bytes
108 * @v key ARC4 encryption key
109 * @v keylen Key length
110 * @v skip Number of bytes of keystream to skip
111 * @v src Message to encrypt or decrypt
112 * @v msglen Length of message
113 * @ret dst Encrypted or decrypted message
115 void arc4_skip ( const void *key
, size_t keylen
, size_t skip
,
116 const void *src
, void *dst
, size_t msglen
)
119 arc4_setkey ( &ctx
, key
, keylen
);
120 arc4_xor ( &ctx
, NULL
, NULL
, skip
);
121 arc4_xor ( &ctx
, src
, dst
, msglen
);
124 struct cipher_algorithm arc4_algorithm
= {
126 .ctxsize
= ARC4_CTX_SIZE
,
128 .setkey
= arc4_setkey
,