crypto/arc4.c

   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
  15 #include <crypto/algapi.h>
  16 #include <crypto/arc4.h>
  17 #include <crypto/internal/skcipher.h>
  18 #include <linux/init.h>
  19 #include <linux/module.h>
  20
  21 struct arc4_ctx {
  22         u32 S[256];
  23         u32 x, y;
  24 };
  25
  26 static int arc4_set_key(struct crypto_tfm *tfm, const u8 *in_key,
  27                         unsigned int key_len)
  28 {
  29         struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
  30         int i, j = 0, k = 0;
  31
  32         ctx->x = 1;
  33         ctx->y = 0;
  34
  35         for (i = 0; i < 256; i++)
  36                 ctx->S[i] = i;
  37
  38         for (i = 0; i < 256; i++) {
  39                 u32 a = ctx->S[i];
  40                 j = (j + in_key[k] + a) & 0xff;
  41                 ctx->S[i] = ctx->S[j];
  42                 ctx->S[j] = a;
  43                 if (++k >= key_len)
  44                         k = 0;
  45         }
  46
  47         return 0;
  48 }
  49
  50 static int arc4_set_key_skcipher(struct crypto_skcipher *tfm, const u8 *in_key,
  51                                  unsigned int key_len)
  52 {
  53         return arc4_set_key(&tfm->base, in_key, key_len);
  54 }
  55
  56 static void arc4_crypt(struct arc4_ctx *ctx, u8 *out, const u8 *in,
  57                        unsigned int len)
  58 {
  59         u32 *const S = ctx->S;
  60         u32 x, y, a, b;
  61         u32 ty, ta, tb;
  62
  63         if (len == 0)
  64                 return;
  65
  66         x = ctx->x;
  67         y = ctx->y;
  68
  69         a = S[x];
  70         y = (y + a) & 0xff;
  71         b = S[y];
  72
  73         do {
  74                 S[y] = a;
  75                 a = (a + b) & 0xff;
  76                 S[x] = b;
  77                 x = (x + 1) & 0xff;
  78                 ta = S[x];
  79                 ty = (y + ta) & 0xff;
  80                 tb = S[ty];
  81                 *out++ = *in++ ^ S[a];
  82                 if (--len == 0)
  83                         break;
  84                 y = ty;
  85                 a = ta;
  86                 b = tb;
  87         } while (true);
  88
  89         ctx->x = x;
  90         ctx->y = y;
  91 }
  92
  93 static void arc4_crypt_one(struct crypto_tfm *tfm, u8 *out, const u8 *in)
  94 {
  95         arc4_crypt(crypto_tfm_ctx(tfm), out, in, 1);
  96 }
  97
  98 static int ecb_arc4_crypt(struct skcipher_request *req)
  99 {
 100         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 101         struct arc4_ctx *ctx = crypto_skcipher_ctx(tfm);
 102         struct skcipher_walk walk;
 103         int err;
 104
 105         err = skcipher_walk_virt(&walk, req, false);
 106
 107         while (walk.nbytes > 0) {
 108                 arc4_crypt(ctx, walk.dst.virt.addr, walk.src.virt.addr,
 109                            walk.nbytes);
 110                 err = skcipher_walk_done(&walk, 0);
 111         }
 112
 113         return err;
 114 }
 115
 116 static struct crypto_alg arc4_cipher = {
 117         .cra_name               =       "arc4",
 118         .cra_flags              =       CRYPTO_ALG_TYPE_CIPHER,
 119         .cra_blocksize          =       ARC4_BLOCK_SIZE,
 120         .cra_ctxsize            =       sizeof(struct arc4_ctx),
 121         .cra_module             =       THIS_MODULE,
 122         .cra_u                  =       {
 123                 .cipher = {
 124                         .cia_min_keysize        =       ARC4_MIN_KEY_SIZE,
 125                         .cia_max_keysize        =       ARC4_MAX_KEY_SIZE,
 126                         .cia_setkey             =       arc4_set_key,
 127                         .cia_encrypt            =       arc4_crypt_one,
 128                         .cia_decrypt            =       arc4_crypt_one,
 129                 },
 130         },
 131 };
 132
 133 static struct skcipher_alg arc4_skcipher = {
 134         .base.cra_name          =       "ecb(arc4)",
 135         .base.cra_priority      =       100,
 136         .base.cra_blocksize     =       ARC4_BLOCK_SIZE,
 137         .base.cra_ctxsize       =       sizeof(struct arc4_ctx),
 138         .base.cra_module        =       THIS_MODULE,
 139         .min_keysize            =       ARC4_MIN_KEY_SIZE,
 140         .max_keysize            =       ARC4_MAX_KEY_SIZE,
 141         .setkey                 =       arc4_set_key_skcipher,
 142         .encrypt                =       ecb_arc4_crypt,
 143         .decrypt                =       ecb_arc4_crypt,
 144 };
 145
 146 static int __init arc4_init(void)
 147 {
 148         int err;
 149
 150         err = crypto_register_alg(&arc4_cipher);
 151         if (err)
 152                 return err;
 153
 154         err = crypto_register_skcipher(&arc4_skcipher);
 155         if (err)
 156                 crypto_unregister_alg(&arc4_cipher);
 157         return err;
 158 }
 159
 160 static void __exit arc4_exit(void)
 161 {
 162         crypto_unregister_alg(&arc4_cipher);
 163         crypto_unregister_skcipher(&arc4_skcipher);
 164 }
 165
 166 module_init(arc4_init);
 167 module_exit(arc4_exit);
 168
 169 MODULE_LICENSE("GPL");
 170 MODULE_DESCRIPTION("ARC4 Cipher Algorithm");
 171 MODULE_AUTHOR("Jon Oberheide <jon@oberheide.org>");
 172 MODULE_ALIAS_CRYPTO("arc4");