string openssl_random_pseudo_bytes ( int $length [, bool &$crypto_strong ] )
Generates a string of pseudo-random bytes, with the number of bytes determined by the length parameter. It also indicates if a cryptographically strong algorithm was used to produce the pseudo-random bytes, and does this via the optional crypto_strong parameter. It's rare for this to be FALSE, but some systems may be broken or old.
Returns the generated string of bytes on success, or FALSE on failure.