git.sur5r.net Git - openldap/blob - libraries/liblutil/entropy.c

   1 /* $OpenLDAP$ */
   2 /*
   3  * Copyright 1998-1999 The OpenLDAP Foundation, All Rights Reserved.
   4  * COPYING RESTRICTIONS APPLY, see COPYRIGHT file
   5  */
   6
   7 #include "portable.h"
   8
   9 #include <fcntl.h>
  10
  11 #include <lutil.h>
  12 #include <lutil_md5.h>
  13
  14 /*
  15  * lutil_entropy() provides nbytes of entropy in buf.
  16  * Quality offerred is suitable for one-time uses, such as "once" keys.
  17  */
  18 int lutil_entropy( char *buf, int nbytes )
  19 {
  20         if( nbytes < 0 ) return -1;
  21         if( nbytes == 0 ) return 0;
  22
  23 #undef URANDOM_DEVICE
  24 #ifdef URANDOM_DEVICE
  25         /* Linux and *BSD offer a urandom device */
  26         {
  27                 int rc, fd;
  28
  29                 fd = open( URANDOM_DEVICE, O_RDONLY );
  30
  31                 if( fd < 0 ) return -1;
  32
  33                 rc = read( fd, buf, nbytes );
  34                 close(fd);
  35
  36                 /* should return nbytes */
  37                 if( rc < nbytes ) return -1;
  38
  39                 return 0;
  40         }
  41 #else
  42         {
  43                 /* based upon Phil Karn's "practical randomness" idea
  44                  * but implementation 100% OpenLDAP.  So don't blame Phil. */
  45                 /* worse case is this is a MD5 hash of a counter, if
  46                  *      MD5 is a strong cryptographic hash, this should
  47                  *      be fairly resisant to attack
  48                  */
  49                 static int initialized = 0;
  50                 int n;
  51
  52                 struct {
  53                         pid_t   pid;
  54
  55 #ifdef HAVE_GETTIMEOFDAY
  56                         struct timeval *tv;
  57 #else
  58                         time_t  time;
  59 #endif
  60                         unsigned long   junk;
  61                 } rdata;
  62
  63                 if( !initialized ) {
  64                         initialized++;
  65
  66                         rdata.pid = getpid();
  67                 }
  68
  69                 for( n = 0; n < nbytes; n += 16 ) {
  70                         struct lutil_MD5Context ctx;
  71                         char digest[16];
  72
  73 #ifdef HAVE_GETTIMEOFDAY
  74                         (void) gettimeofday( &rdata.tv, sizeof( rdata.tv ) );
  75 #else
  76                         (void) time( &rdata.time );
  77 #endif
  78
  79                         rdata.pid++;
  80                         rdata.junk++;
  81
  82                         lutil_MD5Init( &ctx );
  83                         lutil_MD5Update( &ctx, (char *) &rdata, sizeof( rdata ) );
  84                         lutil_MD5Final( digest, &ctx );
  85
  86                         memcpy( &buf[n], digest,
  87                                 nbytes - n > 16 ? 16 : nbytes - n );
  88                 }
  89
  90                 return 0;
  91         }
  92 #endif
  93         return -1;
  94 }