root/crypto/arc4.c

DEFINITIONS

1. arc4_set_key
2. arc4_crypt
3. arc4_init
4. arc4_exit

/* 
 * 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>");