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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>");