arc4.c
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/*
* Cryptographic API
*
* ARC4 Cipher Algorithm
*
* Jon Oberheide <jon@oberheide.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
*/
#include <linux/module.h>
#include <linux/init.h>
#include <linux/crypto.h>
#define ARC4_MIN_KEY_SIZE 1
#define ARC4_MAX_KEY_SIZE 256
#define ARC4_BLOCK_SIZE 1
struct arc4_ctx {
u8 S[256];
u8 x, y;
};
static int arc4_set_key(struct crypto_tfm *tfm, const u8 *in_key,
unsigned int key_len)
{
struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
int i, j = 0, k = 0;
ctx->x = 1;
ctx->y = 0;
for(i = 0; i < 256; i++)
ctx->S[i] = i;
for(i = 0; i < 256; i++)
{
u8 a = ctx->S[i];
j = (j + in_key[k] + a) & 0xff;
ctx->S[i] = ctx->S[j];
ctx->S[j] = a;
if(++k >= key_len)
k = 0;
}
return 0;
}
static void arc4_crypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
{
struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
u8 *const S = ctx->S;
u8 x = ctx->x;
u8 y = ctx->y;
u8 a, b;
a = S[x];
y = (y + a) & 0xff;
b = S[y];
S[x] = b;
S[y] = a;
x = (x + 1) & 0xff;
*out++ = *in ^ S[(a + b) & 0xff];
ctx->x = x;
ctx->y = y;
}
static struct crypto_alg arc4_alg = {
.cra_name = "arc4",
.cra_flags = CRYPTO_ALG_TYPE_CIPHER,
.cra_blocksize = ARC4_BLOCK_SIZE,
.cra_ctxsize = sizeof(struct arc4_ctx),
.cra_module = THIS_MODULE,
.cra_list = LIST_HEAD_INIT(arc4_alg.cra_list),
.cra_u = { .cipher = {
.cia_min_keysize = ARC4_MIN_KEY_SIZE,
.cia_max_keysize = ARC4_MAX_KEY_SIZE,
.cia_setkey = arc4_set_key,
.cia_encrypt = arc4_crypt,
.cia_decrypt = arc4_crypt } }
};
static int __init arc4_init(void)
{
return crypto_register_alg(&arc4_alg);
}
static void __exit arc4_exit(void)
{
crypto_unregister_alg(&arc4_alg);
}
module_init(arc4_init);
module_exit(arc4_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("ARC4 Cipher Algorithm");
MODULE_AUTHOR("Jon Oberheide <jon@oberheide.org>");