This is a hack to address a short-term problem.
We needed to quickly append some unique suffixes to some strings to resist hostile "guessing" or predicting of them.
I started with a fork of Sweelix\guid for PHP.
Sweelix\guid is a PHP 5.3+ library for creating GUIDs.
I added entropy by feeding a v4 UUID into the generation all 3 UUID types.
I also attempted to add additional entropy to the UUID generation for v3 & v5 UUIDs by building another large input using repeated calls to mt_rand() along with a temporal component from microtime() as a nod to the rfc.
If the context of this challenge had been on a Linux server, we may have just used:
cat /proc/sys/kernel/random/uuid
REFERENCES:
GUID/UUID Guidance https://www.ietf.org/rfc/rfc4122.txt
https://en.wikipedia.org/wiki/Universally_unique_identifier
and https://en.wikipedia.org/wiki/Globally_unique_identifier.
Requires class Guid.php from https://github.com/pgaultier/guid.