Shorter GUIDs than hashing a user id?

Posted by Alex Mcp on Stack Overflow See other posts from Stack Overflow or by Alex Mcp
Published on 2011-01-11T03:41:20Z Indexed on 2011/01/11 4:53 UTC
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php

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guid

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user-management

I'm wondering how Instapaper (bookmarklet that saves text) might generate URLs for their bookmarklet.

Mine has a script src of something similar to www.instapaper.com/j/AnJHrfoDTRia

The quality of these URLs is that they need to never collide, and not be really guessable (so other people can't save to your account).

I know a simple approach might be to MD5 their email address (presumed to have been checked on signup for uniqueness), but then I'd end up with a super long string. This isn't a huge issue, but I'm wondering what techniques there are for shorter GUIDs that won't collide too often (this is obviously the tradeoff, but 12 characters above is pretty short in my opinion)

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