diff options
Diffstat (limited to 'unix.c')
| -rw-r--r-- | unix.c | 67 |
1 files changed, 67 insertions, 0 deletions
@@ -224,3 +224,70 @@ double gettime() gettimeofday( time, 0 ); return( (double) time->tv_sec + (double) time->tv_usec / 1000000 ); } + +/* A pretty reliable random number generator. Tries to use the /dev/random + devices first, and falls back to the random number generator from libc + when it fails. Opens randomizer devices with O_NONBLOCK to make sure a + lack of entropy won't halt BitlBee. */ +void random_bytes( unsigned char *buf, int count ) +{ + static int use_dev = -1; + + /* Actually this probing code isn't really necessary, is it? */ + if( use_dev == -1 ) + { + if( access( "/dev/random", R_OK ) == 0 || access( "/dev/urandom", R_OK ) == 0 ) + use_dev = 1; + else + { + use_dev = 0; + srand( ( getpid() << 16 ) ^ time( NULL ) ); + } + } + + if( use_dev ) + { + int fd; + + /* At least on Linux, /dev/random can block if there's not + enough entropy. We really don't want that, so if it can't + give anything, use /dev/urandom instead. */ + if( ( fd = open( "/dev/random", O_RDONLY | O_NONBLOCK ) ) >= 0 ) + if( read( fd, buf, count ) == count ) + { + close( fd ); + return; + } + close( fd ); + + /* urandom isn't supposed to block at all, but just to be + sure. If it blocks, we'll disable use_dev and use the libc + randomizer instead. */ + if( ( fd = open( "/dev/urandom", O_RDONLY | O_NONBLOCK ) ) >= 0 ) + if( read( fd, buf, count ) == count ) + { + close( fd ); + return; + } + close( fd ); + + /* If /dev/random blocks once, we'll still try to use it + again next time. If /dev/urandom also fails for some + reason, stick with libc during this session. */ + + use_dev = 0; + srand( ( getpid() << 16 ) ^ time( NULL ) ); + } + + if( !use_dev ) + { + int i; + + /* Possibly the LSB of rand() isn't very random on some + platforms. Seems okay on at least Linux and OSX though. */ + for( i = 0; i < count; i ++ ) + buf[i] = rand() & 0xff; + } +} + + |