arc4.c

 1// SPDX-License-Identifier: GPL-2.0-or-later
 2/*
 3 * Cryptographic API
 4 *
 5 * ARC4 Cipher Algorithm
 6 *
 7 * Jon Oberheide <jon@oberheide.org>
 8 */
 9
10#include <crypto/arc4.h>
11#include <linux/export.h>
12#include <linux/module.h>
13
14int arc4_setkey(struct arc4_ctx *ctx, const u8 *in_key, unsigned int key_len)
15{
16	int i, j = 0, k = 0;
17
18	ctx->x = 1;
19	ctx->y = 0;
20
21	for (i = 0; i < 256; i++)
22		ctx->S[i] = i;
23
24	for (i = 0; i < 256; i++) {
25		u32 a = ctx->S[i];
26
27		j = (j + in_key[k] + a) & 0xff;
28		ctx->S[i] = ctx->S[j];
29		ctx->S[j] = a;
30		if (++k >= key_len)
31			k = 0;
32	}
33
34	return 0;
35}
36EXPORT_SYMBOL(arc4_setkey);
37
38void arc4_crypt(struct arc4_ctx *ctx, u8 *out, const u8 *in, unsigned int len)
39{
40	u32 *const S = ctx->S;
41	u32 x, y, a, b;
42	u32 ty, ta, tb;
43
44	if (len == 0)
45		return;
46
47	x = ctx->x;
48	y = ctx->y;
49
50	a = S[x];
51	y = (y + a) & 0xff;
52	b = S[y];
53
54	do {
55		S[y] = a;
56		a = (a + b) & 0xff;
57		S[x] = b;
58		x = (x + 1) & 0xff;
59		ta = S[x];
60		ty = (y + ta) & 0xff;
61		tb = S[ty];
62		*out++ = *in++ ^ S[a];
63		if (--len == 0)
64			break;
65		y = ty;
66		a = ta;
67		b = tb;
68	} while (true);
69
70	ctx->x = x;
71	ctx->y = y;
72}
73EXPORT_SYMBOL(arc4_crypt);
74
75MODULE_DESCRIPTION("ARC4 Cipher Algorithm");
76MODULE_LICENSE("GPL");