ircd/random.c

   1 /*
   2  * IRC - Internet Relay Chat, ircd/random.c
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 1, or (at your option)
   7  * any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  17  */
  18 /** @file
  19  * @brief 32-bit pseudo-random number generator implementation.
  20  * @version $Id: random.c,v 1.8 2004/10/06 00:22:09 entrope Exp $
  21  */
  22 #include "config.h"
  23
  24 #include "random.h"
  25 #include "client.h"
  26 #include "ircd_log.h"
  27 #include "ircd_md5.h"
  28 #include "ircd_reply.h"
  29 #include "send.h"
  30
  31 #include <string.h>
  32 #include <sys/time.h>
  33
  34 /** Pseudo-random number generator state. */
  35 static struct MD5Context localkey;
  36 /** Next byte position in #localkey to insert at. */
  37 static unsigned int localkey_pos;
  38
  39 /** Add bytes to #localkey.
  40  * This should be fairly resistant to adding non-random bytes, but the
  41  * more random the bytes are, the harder it is for an attacker to
  42  * guess the internal state.
  43  * @param[in] buf Buffer of bytes to add.
  44  * @param[in] count Number of bytes to add.
  45  */
  46 static void
  47 random_add_entropy(const char *buf, unsigned int count)
  48 {
  49   while (count--) {
  50     localkey.in[localkey_pos++] ^= *buf++;
  51     if (localkey_pos >= sizeof(localkey.in))
  52       localkey_pos = 0;
  53   }
  54 }
  55
  56 /** Seed the PRNG with a string.
  57  * @param[in] from Client setting the seed (may be NULL).
  58  * @param[in] fields Input arguments (fields[0] is used).
  59  * @param[in] count Number of input arguments.
  60  * @return Non-zero on success, zero on error.
  61  */
  62 int
  63 random_seed_set(struct Client* from, const char* const* fields, int count)
  64 {
  65   if (count < 1) {
  66     if (from) /* send an error */
  67       return need_more_params(from, "SET");
  68     else {
  69       log_write(LS_CONFIG, L_ERROR, 0, "Not enough fields in F line");
  70       return 0;
  71     }
  72   }
  73
  74   random_add_entropy(fields[0], strlen(fields[0]));
  75   return 1;
  76 }
  77
  78 /** Generate a pseudo-random number.
  79  * This uses the #localkey structure plus current time as input to
  80  * MD5, feeding most of the MD5 output back to #localkey and using one
  81  * output words as the pseudo-random output.
  82  * @return A 32-bit pseudo-random number.
  83  */
  84 unsigned int ircrandom(void)
  85 {
  86   struct timeval tv;
  87   char usec[3];
  88
  89   /* Add some randomness to the pool. */
  90   gettimeofday(&tv, 0);
  91   usec[0] = tv.tv_usec;
  92   usec[1] = tv.tv_usec >> 8;
  93   usec[2] = tv.tv_usec >> 16;
  94   random_add_entropy(usec, 3);
  95
  96   /* Perform MD5 step. */
  97   localkey.buf[0] = 0x67452301;
  98   localkey.buf[1] = 0xefcdab89;
  99   localkey.buf[2] = 0x98badcfe;
 100   localkey.buf[3] = 0x10325476;
 101   MD5Transform(localkey.buf, (uint32*)localkey.in);
 102
 103   /* Feed back 12 bytes of hash value into randomness pool. */
 104   random_add_entropy((char*)localkey.buf, 12);
 105
 106   /* Return the final word of hash, which should not provide any
 107    * useful insight into current pool contents. */
 108   return localkey.buf[3];
 109 }