I'm not at all up on "encryption" algorithms, but it seems that what you want is a two-way algorithm that (a) isn't computationally expensive and (b) yields 'encrypted' data that's encoded in filesystem-friendly strings. It's the last that's got me stumped. Just that thinking "encryption" might give you some ideas for other searches.

How about an alternate scheme: instead of backing things up one file to a node, write out all the user's nodes into a standard format (XML, anybody?): 

<node>
 <title>How I learned to stop worrying and Love the NodeReaper</title>
 <time>December 31, 2001 : 24:00:00</time>
 <node_content>He got rid of those nasty nodes.  nuff said</node_conte
+nt>
</node>

[download]

Then gzip the whole thing, and there's your backup.

Philosophy can be made out of anything. Or less -- Jerry A. Fodor

In reply to Re: Portably transforming a string to a valid filename by arturo
in thread Portably transforming a string to a valid filename by Anonymous Monk

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