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