```   1/*
2 * Cryptographic API
3 *
4 * ARC4 Cipher Algorithm
5 *
6 * Jon Oberheide <jon@oberheide.org>
7 *
8 * This program is free software; you can redistribute it and/or modify
10 * the Free Software Foundation; either version 2 of the License, or
11 * (at your option) any later version.
12 *
13 */
14#include <linux/module.h>
15#include <linux/init.h>
16#include <linux/crypto.h>
17
18#define ARC4_MIN_KEY_SIZE       1
19#define ARC4_MAX_KEY_SIZE       256
20#define ARC4_BLOCK_SIZE         1
21
22struct arc4_ctx {
23        u8 S[256];
24        u8 x, y;
25};
26
27static int arc4_set_key(void *ctx_arg, const u8 *in_key, unsigned int key_len, u32 *flags)
28{
29        struct arc4_ctx *ctx = ctx_arg;
30        int i, j = 0, k = 0;
31
32        ctx->x = 1;
33        ctx->y = 0;
34
35        for(i = 0; i < 256; i++)
36                ctx->S[i] = i;
37
38        for(i = 0; i < 256; i++)
39        {
40                u8 a = ctx->S[i];
41                j = (j + in_key[k] + a) & 0xff;
42                ctx->S[i] = ctx->S[j];
43                ctx->S[j] = a;
44                if(++k >= key_len)
45                        k = 0;
46        }
47
48        return 0;
49}
50
51static void arc4_crypt(void *ctx_arg, u8 *out, const u8 *in)
52{
53        struct arc4_ctx *ctx = ctx_arg;
54
55        u8 *const S = ctx->S;
56        u8 x = ctx->x;
57        u8 y = ctx->y;
58        u8 a, b;
59
60        a = S[x];
61        y = (y + a) & 0xff;
62        b = S[y];
63        S[x] = b;
64        S[y] = a;
65        x = (x + 1) & 0xff;
66        *out++ = *in ^ S[(a + b) & 0xff];
67
68        ctx->x = x;
69        ctx->y = y;
70}
71
72static struct crypto_alg arc4_alg = {
73        .cra_name               =       "arc4",
74        .cra_flags              =       CRYPTO_ALG_TYPE_CIPHER,
75        .cra_blocksize          =       ARC4_BLOCK_SIZE,
76        .cra_ctxsize            =       sizeof(struct arc4_ctx),
77        .cra_module             =       THIS_MODULE,
79        .cra_u                  =       { .cipher = {
80        .cia_min_keysize        =       ARC4_MIN_KEY_SIZE,
81        .cia_max_keysize        =       ARC4_MAX_KEY_SIZE,
82        .cia_setkey             =       arc4_set_key,
83        .cia_encrypt            =       arc4_crypt,
84        .cia_decrypt            =       arc4_crypt } }
85};
86
87static int __init arc4_init(void)
88{
89        return crypto_register_alg(&arc4_alg);
90}
91
92
93static void __exit arc4_exit(void)
94{
95        crypto_unregister_alg(&arc4_alg);
96}
97
98module_init(arc4_init);
99module_exit(arc4_exit);
100