mdw@git.distorted.org.uk Git - disorder/blob - lib/random.c

   1 /*
   2  * This file is part of DisOrder
   3  * Copyright (C) 2008 Richard Kettlewell
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful, but
  11  * WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
  18  * USA
  19  */
  20
  21 /** @file lib/random.c
  22  * @brief Random number generator
  23  *
  24  */
  25
  26 #include <config.h>
  27 #include "types.h"
  28
  29 #include <fcntl.h>
  30 #include <unistd.h>
  31 #include <errno.h>
  32 #include <string.h>
  33
  34 #include "random.h"
  35 #include "log.h"
  36 #include "arcfour.h"
  37
  38 static int random_count;
  39 static int random_fd = -1;
  40 static arcfour_context random_ctx[1];
  41
  42 /** @brief Rekey the RNG
  43  *
  44  * Resets the RNG's key to a random one read from /dev/urandom
  45  */
  46 static void random__rekey(void) {
  47   char key[128];
  48   int n;
  49
  50   if(random_fd < 0) {
  51     if((random_fd = open("/dev/urandom", O_RDONLY)) < 0)
  52       fatal(errno, "opening /dev/urandom");
  53   }
  54   if((n = read(random_fd, key, sizeof key)) < 0)
  55     fatal(errno, "reading from /dev/urandom");
  56   if((size_t)n < sizeof key)
  57     fatal(0, "reading from /dev/urandom: short read");
  58   arcfour_setkey(random_ctx, key, sizeof key);
  59   random_count = 8 * 1024 * 1024;
  60 }
  61
  62 /** @brief Get random bytes
  63  * @param ptr Where to put random bytes
  64  * @param bytes How many random bytes to generate
  65  */
  66 void random_get(uint8_t *ptr, size_t bytes) {
  67   if(random_count == 0)
  68     random__rekey();
  69   /* Encrypting 0s == just returning the keystream */
  70   memset(ptr, 0, bytes);
  71   arcfour_stream(random_ctx, (char *)ptr, (char *)ptr, bytes);
  72   if(bytes > (size_t)random_count)
  73     random_count = 0;
  74   else
  75     random_count -= bytes;
  76 }
  77
  78 /*
  79 Local Variables:
  80 c-basic-offset:2
  81 comment-column:40
  82 fill-column:79
  83 indent-tabs-mode:nil
  84 End:
  85 */