Seems to be a lot of re-invent-the-wheel being suggested.

If you want unique ids (including generating across different machines) and you want random for "security" because you think they are unguessable - then you need ordinary GUIDs. Your random-unguessable requirement is always going to conflict with index performance (if you use this id as a key).

If you want to avoid the perfromance problems of using GUIDs as keys, and you do your security properly, then use sequential GUIDs which are already built into SQL Server for preciseley this purpose. If you don't want to generate the ids in-database, the same funciton is available on the client, or app layer, in windows api.

SQL: NEWSEQUENTIALID()

Client: UuidCreateSequential()