Você procurou por: guid(globally unique identifier) (Coreano - Inglês)

guid(globally unique identifier)
globally-unique identifier

uuid(universally unique identifier)
universally unique identifier

if you need a unique identifier or token and you intend to give out that token to the user via the network (i.e. session cookies), it is recommended that you use something along the lines of
$token = md5( uniqid("")); / / no prefix $better_token = md5(uniqid(rand(),1)); / / better, difficult to guess

uniqid() returns a prefixed unique identifier based on the current time in microseconds. the prefix can be useful for instance if you generate identifiers simultaneously on several hosts that might happen to generate the identifier at the same microsecond. prefix can be up to 114 characters long.
the prefix can be useful for instance if you generate identifiers simultaneously on several hosts that might happen to generate the identifier at the same microsecond.