Summary

Really globally unique IDs in flash and/or javascript clients. Can I do this with an RNG available in current browsers/flash or must I build a composite ID with server-side randomness?

Details

I need to generate globally unique identifiers for objects. I have multiple server-side "systems" written in java that need to be able to exchange ids; each of these systems also has a set of flex/javascript clients that actually generate the IDs for new objects. I need to guarantee global uniqueness across the set of unrelated systems; for instance I need to be able to merge/sync the databases of two independent systems. I must guarantee that there is never a collision between these ids and that I never need to change the id of an object once created. I need to be able to generate ids in flash and javascript clients without contacting the server for every id. A solution that relies on some server provided seed or system id is fine as long as the server isn't contacted too often. A solution that works completely disconnected is preferable. Similarly a solution that requires no upfront registration of systems is preferable to one that relies on a central authority (like the OUI in a MAC address).

I know the obvious solution is "use a UUID generator," such as UIDUtil in flash. This function specifically disclaims global uniqueness. In general, I'm concerned about relying on a PRNG to guarantee global uniqueness.

Proposed solutions

Rely entirely on a secure random number generator in the client.

Flash 11+ has flash.crypto.generateRandomBytes; Javascript has window.crypto but it's pretty new and not supported in IE. There are solutions like