Re: Determining the inverse function operation from a function definition

nmm1@cus.cam.ac.uk (Nick Maclaren)
30 Apr 2005 10:56:55 -0400

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From: nmm1@cus.cam.ac.uk (Nick Maclaren)
Newsgroups: comp.compilers
Date: 30 Apr 2005 10:56:55 -0400
Organization: University of Cambridge, England
References: 05-04-067 05-04-086
Keywords: theory
Posted-Date: 30 Apr 2005 10:56:55 EDT

SM Ryan <wyrmwif@tsoft.org> wrote:
>
>Some function inversions are thought to be inherently difficult;
>cryptography is based on this assumption. For example DES is an
>invertible function that is intentionally hard to invert.


Yes. One then gets onto the interesting difference of whether a
function has an efficient inverse and whether there is an efficient
method of find one of its better inverses. And, in both cases, the
state can be yes, no or unknown.




Regards,
Nick Maclaren.


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