Google Plus user id representation technique

What kind of technique does use Google Plus to generate users' unique ids?

Example

https://plus.google.com/102766325060234825733/posts开发者_StackOverflow

You can only assume that they are randomly generated ID's that are large enough to be generated non-sequentially with sufficient entropy.

The ID's are too big to be stored in a bigint field which is interesting, again probably due to the required entropy and non-sequential requirement (so that nothing can be inferred by comparing userid's).

A simple encryption of a serially generated number, with a secret key can be used to generate the IDs. It can be a 1 way hash, or a decryptable encryption. The reason for not using serial numbers directly is obvious: You can easily guess userids of other users on the network, which can result in Bots scraping the content of the network.