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 <linux/module.h>
  16 #include <linux/init.h>
  17 #include <linux/crypto.h>
  18 #include <crypto/algapi.h>
  19
  20 #define ARC4_MIN_KEY_SIZE       1
  21 #define ARC4_MAX_KEY_SIZE       256
  22 #define ARC4_BLOCK_SIZE         1
  23
  24 struct arc4_ctx {
  25         u32 S[256];
  26         u32 x, y;
  27 };
  28
  29 static int arc4_set_key(struct crypto_tfm *tfm, const u8 *in_key,
  30                         unsigned int key_len)
  31 {
  32         struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
  33         int i, j = 0, k = 0;
  34
  35         ctx->x = 1;
  36         ctx->y = 0;
  37
  38         for (i = 0; i < 256; i++)
  39                 ctx->S[i] = i;
  40
  41         for (i = 0; i < 256; i++) {
  42                 u32 a = ctx->S[i];
  43                 j = (j + in_key[k] + a) & 0xff;
  44                 ctx->S[i] = ctx->S[j];
  45                 ctx->S[j] = a;
  46                 if (++k >= key_len)
  47                         k = 0;
  48         }
  49
  50         return 0;
  51 }
  52
  53 static void arc4_crypt(struct arc4_ctx *ctx, u8 *out, const u8 *in,
  54                        unsigned int len)
  55 {
  56         u32 *const S = ctx->S;
  57         u32 x, y, a, b;
  58         u32 ty, ta, tb;
  59
  60         if (len == 0)
  61                 return;
  62
  63         x = ctx->x;
  64         y = ctx->y;
  65
  66         a = S[x];
  67         y = (y + a) & 0xff;
  68         b = S[y];
  69
  70         do {
  71                 S[y] = a;
  72                 a = (a + b) & 0xff;
  73                 S[x] = b;
  74                 x = (x + 1) & 0xff;
  75                 ta = S[x];
  76                 ty = (y + ta) & 0xff;
  77                 tb = S[ty];
  78                 *out++ = *in++ ^ S[a];
  79                 if (--len == 0)
  80                         break;
  81                 y = ty;
  82                 a = ta;
  83                 b = tb;
  84         } while (true);
  85
  86         ctx->x = x;
  87         ctx->y = y;
  88 }
  89
  90 static void arc4_crypt_one(struct crypto_tfm *tfm, u8 *out, const u8 *in)
  91 {
  92         arc4_crypt(crypto_tfm_ctx(tfm), out, in, 1);
  93 }
  94
  95 static int ecb_arc4_crypt(struct blkcipher_desc *desc, struct scatterlist *dst,
  96                           struct scatterlist *src, unsigned int nbytes)
  97 {
  98         struct arc4_ctx *ctx = crypto_blkcipher_ctx(desc->tfm);
  99         struct blkcipher_walk walk;
 100         int err;
 101
 102         blkcipher_walk_init(&walk, dst, src, nbytes);
 103
 104         err = blkcipher_walk_virt(desc, &walk);
 105
 106         while (walk.nbytes > 0) {
 107                 u8 *wsrc = walk.src.virt.addr;
 108                 u8 *wdst = walk.dst.virt.addr;
 109
 110                 arc4_crypt(ctx, wdst, wsrc, walk.nbytes);
 111
 112                 err = blkcipher_walk_done(desc, &walk, 0);
 113         }
 114
 115         return err;
 116 }
 117
 118 static struct crypto_alg arc4_algs[2] = { {
 119         .cra_name               =       "arc4",
 120         .cra_flags              =       CRYPTO_ALG_TYPE_CIPHER,
 121         .cra_blocksize          =       ARC4_BLOCK_SIZE,
 122         .cra_ctxsize            =       sizeof(struct arc4_ctx),
 123         .cra_module             =       THIS_MODULE,
 124         .cra_u                  =       {
 125                 .cipher = {
 126                         .cia_min_keysize        =       ARC4_MIN_KEY_SIZE,
 127                         .cia_max_keysize        =       ARC4_MAX_KEY_SIZE,
 128                         .cia_setkey             =       arc4_set_key,
 129                         .cia_encrypt            =       arc4_crypt_one,
 130                         .cia_decrypt            =       arc4_crypt_one,
 131                 },
 132         },
 133 }, {
 134         .cra_name               =       "ecb(arc4)",
 135         .cra_priority           =       100,
 136         .cra_flags              =       CRYPTO_ALG_TYPE_BLKCIPHER,
 137         .cra_blocksize          =       ARC4_BLOCK_SIZE,
 138         .cra_ctxsize            =       sizeof(struct arc4_ctx),
 139         .cra_alignmask          =       0,
 140         .cra_type               =       &crypto_blkcipher_type,
 141         .cra_module             =       THIS_MODULE,
 142         .cra_u                  =       {
 143                 .blkcipher = {
 144                         .min_keysize    =       ARC4_MIN_KEY_SIZE,
 145                         .max_keysize    =       ARC4_MAX_KEY_SIZE,
 146                         .setkey         =       arc4_set_key,
 147                         .encrypt        =       ecb_arc4_crypt,
 148                         .decrypt        =       ecb_arc4_crypt,
 149                 },
 150         },
 151 } };
 152
 153 static int __init arc4_init(void)
 154 {
 155         return crypto_register_algs(arc4_algs, ARRAY_SIZE(arc4_algs));
 156 }
 157
 158 static void __exit arc4_exit(void)
 159 {
 160         crypto_unregister_algs(arc4_algs, ARRAY_SIZE(arc4_algs));
 161 }
 162
 163 module_init(arc4_init);
 164 module_exit(arc4_exit);
 165
 166 MODULE_LICENSE("GPL");
 167 MODULE_DESCRIPTION("ARC4 Cipher Algorithm");
 168 MODULE_AUTHOR("Jon Oberheide <jon@oberheide.org>");