lib/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/arc4.h>
  11 #include <linux/module.h>
  12
  13 int arc4_setkey(struct arc4_ctx *ctx, const u8 *in_key, unsigned int key_len)
  14 {
  15         int i, j = 0, k = 0;
  16
  17         ctx->x = 1;
  18         ctx->y = 0;
  19
  20         for (i = 0; i < 256; i++)
  21                 ctx->S[i] = i;
  22
  23         for (i = 0; i < 256; i++) {
  24                 u32 a = ctx->S[i];
  25
  26                 j = (j + in_key[k] + a) & 0xff;
  27                 ctx->S[i] = ctx->S[j];
  28                 ctx->S[j] = a;
  29                 if (++k >= key_len)
  30                         k = 0;
  31         }
  32
  33         return 0;
  34 }
  35 EXPORT_SYMBOL(arc4_setkey);
  36
  37 void arc4_crypt(struct arc4_ctx *ctx, u8 *out, const u8 *in, unsigned int len)
  38 {
  39         u32 *const S = ctx->S;
  40         u32 x, y, a, b;
  41         u32 ty, ta, tb;
  42
  43         if (len == 0)
  44                 return;
  45
  46         x = ctx->x;
  47         y = ctx->y;
  48
  49         a = S[x];
  50         y = (y + a) & 0xff;
  51         b = S[y];
  52
  53         do {
  54                 S[y] = a;
  55                 a = (a + b) & 0xff;
  56                 S[x] = b;
  57                 x = (x + 1) & 0xff;
  58                 ta = S[x];
  59                 ty = (y + ta) & 0xff;
  60                 tb = S[ty];
  61                 *out++ = *in++ ^ S[a];
  62                 if (--len == 0)
  63                         break;
  64                 y = ty;
  65                 a = ta;
  66                 b = tb;
  67         } while (true);
  68
  69         ctx->x = x;
  70         ctx->y = y;
  71 }
  72 EXPORT_SYMBOL(arc4_crypt);
  73
  74 MODULE_LICENSE("GPL");