Re: [Cfrg] Help with the use of contexts

Tibor Jager <> Fri, 03 February 2017 08:16 UTC

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From: Tibor Jager <>
Date: Fri, 03 Feb 2017 09:16:11 +0100
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Subject: Re: [Cfrg] Help with the use of contexts
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On 30 January 2017 at 12:40, Paterson, Kenny <>

> So: does anyone else want to offer an opinion on the question of contexts?
Contexts are a clean and relatively simple way to prevent cross-protocol
attacks, in particular when implemented in an as simple way as proposed
by Adam and Dan.

The cross-protocol attacks we have seen so far were mostly rather
academic and not too practical. However, with an increasing number of
cryptographic protocols in use the occurrence of practical
cross-protocol attacks becomes much more likely, as the number of
possible combinations grows quadratically. At some point it will become
infeasible to analyze all possible combinations thoroughly enough.

I think at some point in the future we will have to deal with the
prevention of cross-protocol attacks by using contexts, and doing this
as early as possible is a good idea - following the "better safe than
sorry" principle is always a good idea when designing security protocols.