Root/crypto/arc4.c

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
9 * it under the terms of the GNU General Public License as published by
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(struct crypto_tfm *tfm, const u8 *in_key,
28            unsigned int key_len)
29{
30    struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
31    int i, j = 0, k = 0;
32
33    ctx->x = 1;
34    ctx->y = 0;
35
36    for(i = 0; i < 256; i++)
37        ctx->S[i] = i;
38
39    for(i = 0; i < 256; i++)
40    {
41        u8 a = ctx->S[i];
42        j = (j + in_key[k] + a) & 0xff;
43        ctx->S[i] = ctx->S[j];
44        ctx->S[j] = a;
45        if(++k >= key_len)
46            k = 0;
47    }
48
49    return 0;
50}
51
52static void arc4_crypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
53{
54    struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
55
56    u8 *const S = ctx->S;
57    u8 x = ctx->x;
58    u8 y = ctx->y;
59    u8 a, b;
60
61    a = S[x];
62    y = (y + a) & 0xff;
63    b = S[y];
64    S[x] = b;
65    S[y] = a;
66    x = (x + 1) & 0xff;
67    *out++ = *in ^ S[(a + b) & 0xff];
68
69    ctx->x = x;
70    ctx->y = y;
71}
72
73static struct crypto_alg arc4_alg = {
74    .cra_name = "arc4",
75    .cra_flags = CRYPTO_ALG_TYPE_CIPHER,
76    .cra_blocksize = ARC4_BLOCK_SIZE,
77    .cra_ctxsize = sizeof(struct arc4_ctx),
78    .cra_module = THIS_MODULE,
79    .cra_list = LIST_HEAD_INIT(arc4_alg.cra_list),
80    .cra_u = { .cipher = {
81    .cia_min_keysize = ARC4_MIN_KEY_SIZE,
82    .cia_max_keysize = ARC4_MAX_KEY_SIZE,
83    .cia_setkey = arc4_set_key,
84    .cia_encrypt = arc4_crypt,
85    .cia_decrypt = arc4_crypt } }
86};
87
88static int __init arc4_init(void)
89{
90    return crypto_register_alg(&arc4_alg);
91}
92
93
94static void __exit arc4_exit(void)
95{
96    crypto_unregister_alg(&arc4_alg);
97}
98
99module_init(arc4_init);
100module_exit(arc4_exit);
101
102MODULE_LICENSE("GPL");
103MODULE_DESCRIPTION("ARC4 Cipher Algorithm");
104MODULE_AUTHOR("Jon Oberheide <jon@oberheide.org>");
105

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