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 #include "basen.h"
  38 #include "mem.h"
  39
  40 static int random_count;
  41 static int random_fd = -1;
  42 static arcfour_context random_ctx[1];
  43
  44 /** @brief Rekey the RNG
  45  *
  46  * Resets the RNG's key to a random one read from /dev/urandom
  47  */
  48 static void random__rekey(void) {
  49   char key[128];
  50   int n;
  51
  52   if(random_fd < 0) {
  53     if((random_fd = open("/dev/urandom", O_RDONLY)) < 0)
  54       fatal(errno, "opening /dev/urandom");
  55   }
  56   if((n = read(random_fd, key, sizeof key)) < 0)
  57     fatal(errno, "reading from /dev/urandom");
  58   if((size_t)n < sizeof key)
  59     fatal(0, "reading from /dev/urandom: short read");
  60   arcfour_setkey(random_ctx, key, sizeof key);
  61   random_count = 8 * 1024 * 1024;
  62 }
  63
  64 /** @brief Get random bytes
  65  * @param ptr Where to put random bytes
  66  * @param bytes How many random bytes to generate
  67  */
  68 void random_get(void *ptr, size_t bytes) {
  69   if(random_count == 0)
  70     random__rekey();
  71   /* Encrypting 0s == just returning the keystream */
  72   memset(ptr, 0, bytes);
  73   arcfour_stream(random_ctx, (char *)ptr, (char *)ptr, bytes);
  74   if(bytes > (size_t)random_count)
  75     random_count = 0;
  76   else
  77     random_count -= bytes;
  78 }
  79
  80 /** @brief Return a random ID string */
  81 char *random_id(void) {
  82   unsigned long words[2];
  83   char id[128];
  84
  85   random_get(words, sizeof words);
  86   basen(words, sizeof words / sizeof *words, id, sizeof id, 62);
  87   return xstrdup(id);
  88 }
  89
  90 /*
  91 Local Variables:
  92 c-basic-offset:2
  93 comment-column:40
  94 fill-column:79
  95 indent-tabs-mode:nil
  96 End:
  97 */