

The 32-bit cryptographically strong unique ID based on the counter. - acqq
http://www.quora.com/How-do-you-symmetrically-encrypt-32-bit-auto-increment-IDs-to-avoid-using-64-bit-UUIDs-to-conceal-the-size-and-order-of-a-database-table/answers/23925

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kristianp
This is interesting:

"Primary keys are exposed everywhere on the Internet (e.g. Reddit, Quora,
Facebook, etc). I've written numerous crawlers myself and know that this is an
issue. You'll be surprised what these IDs reveal about a company."

