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nbase_rnd.c

/***************************************************************************
 * nbase_rnd.c -- Some simple routines for obtaining random numbers for    *
 * casual use.  These are pretty secure on systems with /dev/urandom, but  *
 * falls back to poor entropy on systems without such support.             *
 *                                                                         *
 ***********************IMPORTANT NMAP LICENSE TERMS************************
 *                                                                         *
 * The Nmap Security Scanner is (C) 1996-2006 Insecure.Com LLC. Nmap is    *
 * also a registered trademark of Insecure.Com LLC.  This program is free  *
 * software; you may redistribute and/or modify it under the terms of the  *
 * GNU General Public License as published by the Free Software            *
 * Foundation; Version 2 with the clarifications and exceptions described  *
 * below.  This guarantees your right to use, modify, and redistribute     *
 * this software under certain conditions.  If you wish to embed Nmap      *
 * technology into proprietary software, we sell alternative licenses      *
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 * detection, and version detection.                                       *
 *                                                                         *
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 * following:                                                              *
 * o Integrates source code from Nmap                                      *
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 *   not derivative works.)                                                * 
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 *                                                                         *
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 *                                                                         *
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 * OpenSSL library which is distributed under a license identical to that  *
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 * but you are not obligated to do so.                                     *
 *                                                                         *
 * If you received these files with a written license agreement or         *
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 *                                                                         *
 * Source is provided to this software because we believe users have a     *
 * right to know exactly what a program is going to do before they run it. *
 * This also allows you to audit the software for security holes (none     *
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 *                                                                         *
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 *                                                                         *
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 * General Public License for more details at                              *
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 * with Nmap.                                                              *
 *                                                                         *
 ***************************************************************************/

/* $Id: nbase_rnd.c 3899 2006-08-29 05:42:35Z fyodor $ */

#include "nbase.h"
#include <string.h>
#include <stdio.h>
#if HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

int get_random_bytes(void *buf, int numbytes) {
  static char bytebuf[2048];
  static char badrandomwarning = 0;
  static int bytesleft = 0;
  int tmp;
  int res;
  struct timeval tv;
  FILE *fp = NULL;
  unsigned int i;
  short *iptr;
  
  if (numbytes < 0 || numbytes > 0xFFFF) return -1;
  
  if (bytesleft == 0) {
    fp = fopen("/dev/arandom", "r");
    if (!fp) fp = fopen("/dev/urandom", "r");
    if (!fp) fp = fopen("/dev/random", "r");
    if (fp) {
      res = (int) fread(bytebuf, 1, sizeof(bytebuf), fp);
      if (res != sizeof(bytebuf)) {    
      fprintf(stderr, "Failed to read from /dev/urandom or /dev/random\n");
      fclose(fp);
      fp = NULL;
      }      
      bytesleft = sizeof(bytebuf);
    }
    if (!fp) {  
      if (badrandomwarning == 0) {
      badrandomwarning++;
      /*      error("WARNING: your system apparently does not offer /dev/urandom or /dev/random.  Reverting to less secure version."); */
      
      /* Seed our random generator */
      gettimeofday(&tv, NULL);
      srand((tv.tv_sec ^ tv.tv_usec) ^ getpid());
      }
      
      for(i=0; i < sizeof(bytebuf) / sizeof(short); i++) {
      iptr = (short *) ((char *)bytebuf + i * sizeof(short));
      *iptr = rand();
      }
      bytesleft = (sizeof(bytebuf) / sizeof(short)) * sizeof(short);
      /*    ^^^^^^^^^^^^^^^not as meaningless as it looks  */
    } else fclose(fp);
  }
  
  if (numbytes <= bytesleft) { /* we can cover it */
    memcpy(buf, bytebuf + (sizeof(bytebuf) - bytesleft), numbytes);
    bytesleft -= numbytes;
    return 0;
  }
  
  /* We don't have enough */
  memcpy(buf, bytebuf + (sizeof(bytebuf) - bytesleft), bytesleft);
  tmp = bytesleft;
  bytesleft = 0;
  return get_random_bytes((char *)buf + tmp, numbytes - tmp);
}

int get_random_int() {
  int i;
  get_random_bytes(&i, sizeof(int));
  return i;
}

unsigned int get_random_uint() {
  unsigned int i;
  get_random_bytes(&i, sizeof(unsigned int));
  return i;
}

u32 get_random_u32() {
  u32 i;
  get_random_bytes(&i, sizeof(i));
  return i;
}

u16 get_random_u16() {
  u16 i;
  get_random_bytes(&i, sizeof(i));
  return i;
}

u8 get_random_u8() {
  u8 i;
  get_random_bytes(&i, sizeof(i));
  return i;
}

unsigned short get_random_ushort() {
  unsigned short s;
  get_random_bytes(&s, sizeof(unsigned short));
  return s;
}

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