Changeset 1a57b893 for unix.c


Ignore:
Timestamp:
2008-04-02T15:12:26Z (12 years ago)
Author:
Jelmer Vernooij <jelmer@…>
Branches:
master
Children:
e46e077
Parents:
0a14b8c (diff), 5be87b2 (diff)
Note: this is a merge changeset, the changes displayed below correspond to the merge itself.
Use the (diff) links above to see all the changes relative to each parent.
Message:

Merge move of random_bytes().

File:
1 edited

Legend:

Unmodified
Added
Removed
  • unix.c

    r0a14b8c r1a57b893  
    225225        return( (double) time->tv_sec + (double) time->tv_usec / 1000000 );
    226226}
     227
     228/* A pretty reliable random number generator. Tries to use the /dev/random
     229   devices first, and falls back to the random number generator from libc
     230   when it fails. Opens randomizer devices with O_NONBLOCK to make sure a
     231   lack of entropy won't halt BitlBee. */
     232void random_bytes( unsigned char *buf, int count )
     233{
     234        static int use_dev = -1;
     235       
     236        /* Actually this probing code isn't really necessary, is it? */
     237        if( use_dev == -1 )
     238        {
     239                if( access( "/dev/random", R_OK ) == 0 || access( "/dev/urandom", R_OK ) == 0 )
     240                        use_dev = 1;
     241                else
     242                {
     243                        use_dev = 0;
     244                        srand( ( getpid() << 16 ) ^ time( NULL ) );
     245                }
     246        }
     247       
     248        if( use_dev )
     249        {
     250                int fd;
     251               
     252                /* At least on Linux, /dev/random can block if there's not
     253                   enough entropy. We really don't want that, so if it can't
     254                   give anything, use /dev/urandom instead. */
     255                if( ( fd = open( "/dev/random", O_RDONLY | O_NONBLOCK ) ) >= 0 )
     256                        if( read( fd, buf, count ) == count )
     257                        {
     258                                close( fd );
     259                                return;
     260                        }
     261                close( fd );
     262               
     263                /* urandom isn't supposed to block at all, but just to be
     264                   sure. If it blocks, we'll disable use_dev and use the libc
     265                   randomizer instead. */
     266                if( ( fd = open( "/dev/urandom", O_RDONLY | O_NONBLOCK ) ) >= 0 )
     267                        if( read( fd, buf, count ) == count )
     268                        {
     269                                close( fd );
     270                                return;
     271                        }
     272                close( fd );
     273               
     274                /* If /dev/random blocks once, we'll still try to use it
     275                   again next time. If /dev/urandom also fails for some
     276                   reason, stick with libc during this session. */
     277               
     278                use_dev = 0;
     279                srand( ( getpid() << 16 ) ^ time( NULL ) );
     280        }
     281       
     282        if( !use_dev )
     283        {
     284                int i;
     285               
     286                /* Possibly the LSB of rand() isn't very random on some
     287                   platforms. Seems okay on at least Linux and OSX though. */
     288                for( i = 0; i < count; i ++ )
     289                        buf[i] = rand() & 0xff;
     290        }
     291}
     292
     293
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