linux/crypto/arc4.c
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   1/* 
   2 * Cryptographic API
   3 *
   4 * ARC4 Cipher Algorithm
   5 *
   6 * Jon Oberheide <jon@oberheide.org>
   7 *
   8 * This program is free software; you can redistribute it and/or modify
   9 * it under the terms of the GNU General Public License as published by
  10 * the Free Software Foundation; either version 2 of the License, or
  11 * (at your option) any later version.
  12 *
  13 */
  14#include <linux/module.h>
  15#include <linux/init.h>
  16#include <linux/crypto.h>
  17
  18#define ARC4_MIN_KEY_SIZE       1
  19#define ARC4_MAX_KEY_SIZE       256
  20#define ARC4_BLOCK_SIZE         1
  21
  22struct arc4_ctx {
  23        u8 S[256];
  24        u8 x, y;
  25};
  26
  27static int arc4_set_key(struct crypto_tfm *tfm, const u8 *in_key,
  28                        unsigned int key_len)
  29{
  30        struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
  31        int i, j = 0, k = 0;
  32
  33        ctx->x = 1;
  34        ctx->y = 0;
  35
  36        for(i = 0; i < 256; i++)
  37                ctx->S[i] = i;
  38
  39        for(i = 0; i < 256; i++)
  40        {
  41                u8 a = ctx->S[i];
  42                j = (j + in_key[k] + a) & 0xff;
  43                ctx->S[i] = ctx->S[j];
  44                ctx->S[j] = a;
  45                if(++k >= key_len)
  46                        k = 0;
  47        }
  48
  49        return 0;
  50}
  51
  52static void arc4_crypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
  53{
  54        struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
  55
  56        u8 *const S = ctx->S;
  57        u8 x = ctx->x;
  58        u8 y = ctx->y;
  59        u8 a, b;
  60
  61        a = S[x];
  62        y = (y + a) & 0xff;
  63        b = S[y];
  64        S[x] = b;
  65        S[y] = a;
  66        x = (x + 1) & 0xff;
  67        *out++ = *in ^ S[(a + b) & 0xff];
  68
  69        ctx->x = x;
  70        ctx->y = y;
  71}
  72
  73static struct crypto_alg arc4_alg = {
  74        .cra_name               =       "arc4",
  75        .cra_flags              =       CRYPTO_ALG_TYPE_CIPHER,
  76        .cra_blocksize          =       ARC4_BLOCK_SIZE,
  77        .cra_ctxsize            =       sizeof(struct arc4_ctx),
  78        .cra_module             =       THIS_MODULE,
  79        .cra_list               =       LIST_HEAD_INIT(arc4_alg.cra_list),
  80        .cra_u                  =       { .cipher = {
  81        .cia_min_keysize        =       ARC4_MIN_KEY_SIZE,
  82        .cia_max_keysize        =       ARC4_MAX_KEY_SIZE,
  83        .cia_setkey             =       arc4_set_key,
  84        .cia_encrypt            =       arc4_crypt,
  85        .cia_decrypt            =       arc4_crypt } }
  86};
  87
  88static int __init arc4_init(void)
  89{
  90        return crypto_register_alg(&arc4_alg);
  91}
  92
  93
  94static void __exit arc4_exit(void)
  95{
  96        crypto_unregister_alg(&arc4_alg);
  97}
  98
  99module_init(arc4_init);
 100module_exit(arc4_exit);
 101
 102MODULE_LICENSE("GPL");
 103MODULE_DESCRIPTION("ARC4 Cipher Algorithm");
 104MODULE_AUTHOR("Jon Oberheide <jon@oberheide.org>");
 105
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