arc4.c

Go to the documentation of this file.

/*
 * Cryptographic API
 *
 * ARC4 Cipher Algorithm
 *
 * Jon Oberheide <[email protected]>
 *
 * 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 "rtl_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(void *ctx_arg, const u8 *in_key, unsigned int key_len, u32 *flags)
{
    struct arc4_ctx *ctx = ctx_arg;
    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((unsigned int)++k >= key_len)
            k = 0;
    }

    return 0;
}

static void arc4_crypt(void *ctx_arg, u8 *out, const u8 *in)
{
    struct arc4_ctx *ctx = ctx_arg;

    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 <[email protected]>");