source/lib/genrand.c

   1 /*
   2    Unix SMB/Netbios implementation.
   3    Version 1.9.
   4
   5    Functions to create reasonable random numbers for crypto use.
   6
   7    Copyright (C) Jeremy Allison 1998
   8
   9    This program is free software; you can redistribute it and/or modify
  10    it under the terms of the GNU General Public License as published by
  11    the Free Software Foundation; either version 2 of the License, or
  12    (at your option) any later version.
  13
  14    This program is distributed in the hope that it will be useful,
  15    but WITHOUT ANY WARRANTY; without even the implied warranty of
  16    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17    GNU General Public License for more details.
  18
  19    You should have received a copy of the GNU General Public License
  20    along with this program; if not, write to the Free Software
  21    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  22 */
  23
  24 #include "includes.h"
  25
  26 extern int DEBUGLEVEL;
  27 static uint32 counter = 0;
  28
  29 /****************************************************************
  30 get a 16 byte hash from the contents of a file
  31 Note that the hash is not initialised.
  32 *****************************************************************/
  33 static void do_filehash(char *fname, unsigned char *hash)
  34 {
  35         unsigned char buf[1011]; /* deliberate weird size */
  36         unsigned char tmp_md4[16];
  37         int fd, n;
  38
  39         fd = sys_open(fname,O_RDONLY,0);
  40         if (fd == -1) return;
  41
  42         while ((n = read(fd, (char *)buf, sizeof(buf))) > 0) {
  43                 mdfour(tmp_md4, buf, n);
  44                 for (n=0;n<16;n++)
  45                         hash[n] ^= tmp_md4[n];
  46         }
  47         close(fd);
  48 }
  49
  50
  51
  52 /****************************************************************
  53  Try and get a seed by looking at the atimes of files in a given
  54  directory. XOR them into the buf array.
  55 *****************************************************************/
  56
  57 static void do_dirrand(char *name, unsigned char *buf, int buf_len)
  58 {
  59   DIR *dp = opendir(name);
  60   pstring fullname;
  61   int len_left;
  62   int fullname_len;
  63   char *pos;
  64
  65   pstrcpy(fullname, name);
  66   fullname_len = strlen(fullname);
  67
  68   if(fullname_len + 2 > sizeof(pstring))
  69     return;
  70
  71   if(fullname[fullname_len] != '/') {
  72     fullname[fullname_len] = '/';
  73     fullname[fullname_len+1] = '\0';
  74     fullname_len = strlen(fullname);
  75   }
  76
  77   len_left = sizeof(pstring) - fullname_len - 1;
  78   pos = &fullname[fullname_len];
  79
  80   if(dp != NULL) {
  81     char *p;
  82
  83     while ((p = readdirname(dp))) {
  84       SMB_STRUCT_STAT st;
  85
  86       if(strlen(p) <= len_left)
  87         pstrcpy(pos, p);
  88
  89       if(sys_stat(fullname,&st) == 0) {
  90         SIVAL(buf, ((counter * 4)%(buf_len-4)),
  91               IVAL(buf,((counter * 4)%(buf_len-4))) ^ st.st_atime);
  92         counter++;
  93         DEBUG(10,("do_dirrand: value from file %s.\n", fullname));
  94       }
  95     }
  96     closedir(dp);
  97   }
  98 }
  99
 100 /**************************************************************
 101  Try and get a good random number seed. Try a number of
 102  different factors. Firstly, try /dev/urandom and try and
 103  read from this. If this fails iterate through /tmp and
 104  /dev and XOR all the file timestamps. Next add in
 105  a hash of the contents of /etc/shadow and the smb passwd
 106  file and a combination of pid and time of day (yes I know this
 107  sucks :-). Finally md4 the result.
 108
 109  We use /dev/urandom as a read of /dev/random can block if
 110  the entropy pool dries up. This leads clients to timeout
 111  or be very slow on connect.
 112
 113  The result goes in a 16 byte buffer passed from the caller
 114 **************************************************************/
 115
 116 static uint32 do_reseed(unsigned char *md4_outbuf)
 117 {
 118   unsigned char md4_inbuf[40];
 119   BOOL got_random = False;
 120   uint32 v1, v2, ret;
 121   int fd;
 122   struct timeval tval;
 123   pid_t mypid;
 124   struct passwd *pw;
 125
 126   memset(md4_inbuf, '\0', sizeof(md4_inbuf));
 127
 128   fd = sys_open( "/dev/urandom", O_RDONLY,0);
 129   if(fd >= 0) {
 130     /*
 131      * We can use /dev/urandom !
 132      */
 133     if(read(fd, md4_inbuf, 40) == 40) {
 134       got_random = True;
 135       DEBUG(10,("do_reseed: got 40 bytes from /dev/urandom.\n"));
 136     }
 137     close(fd);
 138   }
 139
 140   if(!got_random) {
 141     /*
 142      * /dev/urandom failed - try /dev for timestamps.
 143      */
 144     do_dirrand("/dev", md4_inbuf, sizeof(md4_inbuf));
 145   }
 146
 147   /* possibly add in some secret file contents */
 148   do_filehash("/etc/shadow", &md4_inbuf[0]);
 149   do_filehash(lp_smb_passwd_file(), &md4_inbuf[16]);
 150
 151   /* add in the root encrypted password. On any system where security is taken
 152      seriously this will be secret */
 153   pw = sys_getpwnam("root");
 154   if (pw && pw->pw_passwd) {
 155           int i;
 156           unsigned char md4_tmp[16];
 157           mdfour(md4_tmp, (unsigned char *)pw->pw_passwd, strlen(pw->pw_passwd));
 158           for (i=0;i<16;i++)
 159                   md4_inbuf[8+i] ^= md4_tmp[i];
 160   }
 161
 162   /*
 163    * Finally add the counter, time of day, and pid.
 164    */
 165   GetTimeOfDay(&tval);
 166   mypid = getpid();
 167   v1 = (counter++) + mypid + tval.tv_sec;
 168   v2 = (counter++) * mypid + tval.tv_usec;
 169
 170   SIVAL(md4_inbuf, 32, v1 ^ IVAL(md4_inbuf, 32));
 171   SIVAL(md4_inbuf, 36, v2 ^ IVAL(md4_inbuf, 36));
 172
 173   mdfour(md4_outbuf, md4_inbuf, sizeof(md4_inbuf));
 174
 175   /*
 176    * Return a 32 bit int created from XORing the
 177    * 16 bit return buffer.
 178    */
 179
 180   ret = IVAL(md4_outbuf, 0);
 181   ret ^= IVAL(md4_outbuf, 4);
 182   ret ^= IVAL(md4_outbuf, 8);
 183   return (ret ^ IVAL(md4_outbuf, 12));
 184 }
 185
 186 /*******************************************************************
 187  Interface to the (hopefully) good crypto random number generator.
 188 ********************************************************************/
 189
 190 void generate_random_buffer( unsigned char *out, int len, BOOL re_seed)
 191 {
 192   static BOOL done_reseed = False;
 193   static unsigned char md4_buf[16];
 194   unsigned char tmp_buf[16];
 195   unsigned char *p;
 196
 197   if(!done_reseed || re_seed) {
 198           sys_srandom(do_reseed(md4_buf));
 199           done_reseed = True;
 200   }
 201
 202   /*
 203    * Generate random numbers in chunks of 64 bytes,
 204    * then md4 them & copy to the output buffer.
 205    * Added XOR with output from random, seeded
 206    * by the original md4_buf. This is to stop the
 207    * output from this function being the previous
 208    * md4_buf md4'ed. The output from this function
 209    * is often output onto the wire, and so it should
 210    * not be possible to guess the next output from
 211    * this function based on the previous output.
 212    * XORing in the output from random(), seeded by
 213    * the original md4 hash should stop this. JRA.
 214    */
 215
 216   p = out;
 217   while(len > 0) {
 218     int i;
 219     int copy_len = len > 16 ? 16 : len;
 220     mdfour(tmp_buf, md4_buf, sizeof(md4_buf));
 221     memcpy(md4_buf, tmp_buf, sizeof(md4_buf));
 222     /* XOR in output from random(). */
 223     for(i = 0; i < 4; i++)
 224       SIVAL(tmp_buf, i*4, (IVAL(tmp_buf, i*4) ^ (uint32)sys_random()));
 225     memcpy(p, tmp_buf, copy_len);
 226     p += copy_len;
 227     len -= copy_len;
 228   }
 229 }