LXR linux/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
  13int 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}
  35EXPORT_SYMBOL(arc4_setkey);
  36
  37void 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}
  72EXPORT_SYMBOL(arc4_crypt);
  73
  74MODULE_LICENSE("GPL");
  75