Re: [Cfrg] matching AES security

Watson Ladd <watsonbladd@gmail.com> Fri, 01 August 2014 03:00 UTC

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Date: Thu, 31 Jul 2014 20:00:22 -0700
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From: Watson Ladd <watsonbladd@gmail.com>
To: Peter Gutmann <pgut001@cs.auckland.ac.nz>
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Subject: Re: [Cfrg] matching AES security
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On Thu, Jul 31, 2014 at 7:13 PM, Peter Gutmann
<pgut001@cs.auckland.ac.nz> wrote:
> Johannes Merkle <johannes.merkle@secunet.com> writes:
>>The attack is very simple:
>>- Gather a list of 2^N cipher texts resulting from the _same_ plain text
>>encrypted under 2^N random keys.
>>- For 2^(128-N) randomly chosen (different) keys, encrypt the known plain
>>text and check if the resulting cipher text matches one of the gathered
>>cipher texts
>
> That attack is *conceptually* very simple, in the same way that getting humans
> to Mars is conceptually very simple:
>
> - Build a rocket capable of travelling to Mars and back.
> - Board rocket and fly to Mars.
>
> Practically, though, some of the steps are a bit tricky.

Except that the issue isn't doing 2^128 calculations: it's what you
have when you have only done 2^70 or so calculations.
The relevant paper is http://cr.yp.to/snuffle/bruteforce-20050425.pdf.

Sincerely,
Watson Ladd

>
> Peter.
>
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