/*

   * 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>");