Re: Idea for a slow block cipher with adjustable block length

From: Antti Louko (alo_at_iki.fi.invalid)
Date: 03/31/05 

Date: 31 Mar 2005 02:20:44 +0300

Paul Rubin <http://phr.cx@NOSPAM.invalid> writes:
> Antti Louko <alo@iki.fi.invalid> writes:

> This is fine and I've done things like it in Python several times.
> You only need 4 rounds, not 20, if the F function is pseudorandom like
> SHA-1 (approximately) is.

Thank you.

> > I think this could be used to implement usable mappings with
> > relatively short block lengths (24 bits). After all, this cipher is
> > not intended to be used in any other mode that pure ECB.

> Such short block lengths are subject to codebook attacks.

In this case the only requirement is that if any number of mappings
are revealed, this doesn't make arbitrary reverse (or direct) mappings
easy to find.

In practice the weaker parts are going to be elsewhere in the system.
If I will get permission, I will describe later what my friend is
trying to accomplish.