openbsd-compat/bsd-arc4random.c

   1 /*
   2  * Copyright (c) 1999,2000,2004 Damien Miller <djm@mindrot.org>
   3  *
   4  * Permission to use, copy, modify, and distribute this software for any
   5  * purpose with or without fee is hereby granted, provided that the above
   6  * copyright notice and this permission notice appear in all copies.
   7  *
   8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  15  */
  16
  17 #include "includes.h"
  18 #include "log.h"
  19
  20 RCSID("$Id: bsd-arc4random.c,v 1.10 2005/02/16 02:01:28 djm Exp $");
  21
  22 #ifndef HAVE_ARC4RANDOM
  23
  24 #include <openssl/rand.h>
  25 #include <openssl/rc4.h>
  26 #include <openssl/err.h>
  27
  28 /* Size of key to use */
  29 #define SEED_SIZE 20
  30
  31 /* Number of bytes to reseed after */
  32 #define REKEY_BYTES     (1 << 24)
  33
  34 static int rc4_ready = 0;
  35 static RC4_KEY rc4;
  36
  37 unsigned int
  38 arc4random(void)
  39 {
  40         unsigned int r = 0;
  41         static int first_time = 1;
  42
  43         if (rc4_ready <= 0) {
  44                 if (first_time)
  45                         seed_rng();
  46                 first_time = 0;
  47                 arc4random_stir();
  48         }
  49
  50         RC4(&rc4, sizeof(r), (unsigned char *)&r, (unsigned char *)&r);
  51
  52         rc4_ready -= sizeof(r);
  53
  54         return(r);
  55 }
  56
  57 void
  58 arc4random_stir(void)
  59 {
  60         unsigned char rand_buf[SEED_SIZE];
  61         int i;
  62
  63         memset(&rc4, 0, sizeof(rc4));
  64         if (RAND_bytes(rand_buf, sizeof(rand_buf)) <= 0)
  65                 fatal("Couldn't obtain random bytes (error %ld)",
  66                     ERR_get_error());
  67         RC4_set_key(&rc4, sizeof(rand_buf), rand_buf);
  68
  69         /*
  70          * Discard early keystream, as per recommendations in:
  71          * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
  72          */
  73         for(i = 0; i <= 256; i += sizeof(rand_buf))
  74                 RC4(&rc4, sizeof(rand_buf), rand_buf, rand_buf);
  75
  76         memset(rand_buf, 0, sizeof(rand_buf));
  77
  78         rc4_ready = REKEY_BYTES;
  79 }
  80 #endif /* !HAVE_ARC4RANDOM */