From: "Hal E. Fulton" <hal9000@...>
Date: 2001-11-13T19:22:37+09:00
Subject: [ruby-talk:25001] Re: Mapping sequential strings to random strings: How would you do this?

----- Original Message -----
From: Niklas Frykholm <niklasf@cs.umu.se>
To: ruby-talk ML <ruby-talk@ruby-lang.org>
Sent: Tuesday, November 13, 2001 3:50 AM
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. ;)

Yes, that works well... thanks very much.

I had quite forgotten that md5 was around... thought it was something I
had to download.

Now, I wonder if there is a way to make the strings shorter? ;)

Hal