crypto/arc4.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Cryptographic API
   4  *
   5  * ARC4 Cipher Algorithm
   6  *
   7  * Jon Oberheide <jon@oberheide.org>
   8  */
   9
  10 #include <crypto/algapi.h>
  11 #include <crypto/arc4.h>
  12 #include <crypto/internal/skcipher.h>
  13 #include <linux/init.h>
  14 #include <linux/module.h>
  15
  16 struct arc4_ctx {
  17         u32 S[256];
  18         u32 x, y;
  19 };
  20
  21 static int arc4_set_key(struct crypto_tfm *tfm, const u8 *in_key,
  22                         unsigned int key_len)
  23 {
  24         struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
  25         int i, j = 0, k = 0;
  26
  27         ctx->x = 1;
  28         ctx->y = 0;
  29
  30         for (i = 0; i < 256; i++)
  31                 ctx->S[i] = i;
  32
  33         for (i = 0; i < 256; i++) {
  34                 u32 a = ctx->S[i];
  35                 j = (j + in_key[k] + a) & 0xff;
  36                 ctx->S[i] = ctx->S[j];
  37                 ctx->S[j] = a;
  38                 if (++k >= key_len)
  39                         k = 0;
  40         }
  41
  42         return 0;
  43 }
  44
  45 static int arc4_set_key_skcipher(struct crypto_skcipher *tfm, const u8 *in_key,
  46                                  unsigned int key_len)
  47 {
  48         return arc4_set_key(&tfm->base, in_key, key_len);
  49 }
  50
  51 static void arc4_crypt(struct arc4_ctx *ctx, u8 *out, const u8 *in,
  52                        unsigned int len)
  53 {
  54         u32 *const S = ctx->S;
  55         u32 x, y, a, b;
  56         u32 ty, ta, tb;
  57
  58         if (len == 0)
  59                 return;
  60
  61         x = ctx->x;
  62         y = ctx->y;
  63
  64         a = S[x];
  65         y = (y + a) & 0xff;
  66         b = S[y];
  67
  68         do {
  69                 S[y] = a;
  70                 a = (a + b) & 0xff;
  71                 S[x] = b;
  72                 x = (x + 1) & 0xff;
  73                 ta = S[x];
  74                 ty = (y + ta) & 0xff;
  75                 tb = S[ty];
  76                 *out++ = *in++ ^ S[a];
  77                 if (--len == 0)
  78                         break;
  79                 y = ty;
  80                 a = ta;
  81                 b = tb;
  82         } while (true);
  83
  84         ctx->x = x;
  85         ctx->y = y;
  86 }
  87
  88 static void arc4_crypt_one(struct crypto_tfm *tfm, u8 *out, const u8 *in)
  89 {
  90         arc4_crypt(crypto_tfm_ctx(tfm), out, in, 1);
  91 }
  92
  93 static int ecb_arc4_crypt(struct skcipher_request *req)
  94 {
  95         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  96         struct arc4_ctx *ctx = crypto_skcipher_ctx(tfm);
  97         struct skcipher_walk walk;
  98         int err;
  99
 100         err = skcipher_walk_virt(&walk, req, false);
 101
 102         while (walk.nbytes > 0) {
 103                 arc4_crypt(ctx, walk.dst.virt.addr, walk.src.virt.addr,
 104                            walk.nbytes);
 105                 err = skcipher_walk_done(&walk, 0);
 106         }
 107
 108         return err;
 109 }
 110
 111 static struct crypto_alg arc4_cipher = {
 112         .cra_name               =       "arc4",
 113         .cra_flags              =       CRYPTO_ALG_TYPE_CIPHER,
 114         .cra_blocksize          =       ARC4_BLOCK_SIZE,
 115         .cra_ctxsize            =       sizeof(struct arc4_ctx),
 116         .cra_module             =       THIS_MODULE,
 117         .cra_u                  =       {
 118                 .cipher = {
 119                         .cia_min_keysize        =       ARC4_MIN_KEY_SIZE,
 120                         .cia_max_keysize        =       ARC4_MAX_KEY_SIZE,
 121                         .cia_setkey             =       arc4_set_key,
 122                         .cia_encrypt            =       arc4_crypt_one,
 123                         .cia_decrypt            =       arc4_crypt_one,
 124                 },
 125         },
 126 };
 127
 128 static struct skcipher_alg arc4_skcipher = {
 129         .base.cra_name          =       "ecb(arc4)",
 130         .base.cra_priority      =       100,
 131         .base.cra_blocksize     =       ARC4_BLOCK_SIZE,
 132         .base.cra_ctxsize       =       sizeof(struct arc4_ctx),
 133         .base.cra_module        =       THIS_MODULE,
 134         .min_keysize            =       ARC4_MIN_KEY_SIZE,
 135         .max_keysize            =       ARC4_MAX_KEY_SIZE,
 136         .setkey                 =       arc4_set_key_skcipher,
 137         .encrypt                =       ecb_arc4_crypt,
 138         .decrypt                =       ecb_arc4_crypt,
 139 };
 140
 141 static int __init arc4_init(void)
 142 {
 143         int err;
 144
 145         err = crypto_register_alg(&arc4_cipher);
 146         if (err)
 147                 return err;
 148
 149         err = crypto_register_skcipher(&arc4_skcipher);
 150         if (err)
 151                 crypto_unregister_alg(&arc4_cipher);
 152         return err;
 153 }
 154
 155 static void __exit arc4_exit(void)
 156 {
 157         crypto_unregister_alg(&arc4_cipher);
 158         crypto_unregister_skcipher(&arc4_skcipher);
 159 }
 160
 161 subsys_initcall(arc4_init);
 162 module_exit(arc4_exit);
 163
 164 MODULE_LICENSE("GPL");
 165 MODULE_DESCRIPTION("ARC4 Cipher Algorithm");
 166 MODULE_AUTHOR("Jon Oberheide <jon@oberheide.org>");
 167 MODULE_ALIAS_CRYPTO("arc4");