From: Niklas Frykholm <niklasf@...>
Date: 2001-11-13T18:50:48+09:00
Subject: [ruby-talk:24995] Re: Mapping sequential strings to random strings: How would you do this?

[Hal E. Fulton]
> But I don't want the names to be "guessable" -- i.e., 
> doc001.html, doc002.html, and so on.
> 
> I'm thinking of keeping some kind of mapping between the
> original names and "scrambled" file names. For example,
> the files might be named xjhfkros.html, 7glcm3lg.html, and
> so on.
...
> Constraints I'd like to see are:
> 1. Fixed-length scrambled strings;
> 2. True one-to-one mapping
> 3. "Reasonable" (printable) characters only
> 4. Non-obvious mapping

What about

	require 'md5'
	secret = 'aljfaweru923jfjkasfljas'

	MD5.md5('doc001.html' + secret).hexdigest + '.html'

Replace the value of secret with some random string known only to you.
It fulfills 1, 2, 3 and 4. (Well it doesn't fulfill 2 in theory, but
collisions are extremely rare. In fact, if you would find a collision,
you would have 'broken' MD5. You could publish it and become famous. ;)

// Niklas