[jandrewrogers]

There have been many cases of UUIDv4 collisions because an RNG wasn’t as random as expected, due to broken RNG or developer error. It is one of those cases where practice is not as reliable as theory, and it is banned in some places as a consequence.

It depends on how paranoid you need to be.

[MichaelZuo]

NIST standards on RNG are not as random as expected?

Or do you mean certain folks intentionally chose substandard implementations for some reason?

[jandrewrogers]

A significant number of implementers roll their own UUIDv4. It seems so easy so why not? Most UUIDs are used in contexts where the devs are not that sophisticated so it isn’t that surprising that naive mistakes happen. If you are using it for distributed UUID generation, it just takes one person making a mistake to create havoc.

UUIDv4 is banned in many high security environments primarily because it is easy for people to screw up in practice and it is difficult to detect when those mistakes are made. 128-bits doesn’t leave much room for mistakes using probabilistic uniqueness.

[polynomial]

Facts.