I just implemented phpass into my websites register code and it seemed to work, but it gave me the following warning
Warning: is_readable(): open_basedir restriction in effect. File(/dev/urandom) is not `within the allowed path(s): (/home/u997733154:/usr/lib/php:/tmp) in /home/u997733154/public_html/PasswordHash.php on line 51`
Look at your php.ini file. There is a restriction in place by default concerning what files you can open.
See this link for more details : http://www.php.net/manual/en/ini.core.php#ini.open-basedir