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RE: [ietf-dkim] Deployment Scenario 7: Cryptographic Upgrade andDowngrade Attacks

2007-02-23 19:10:46

[mailto:ietf-dkim-bounces(_at_)mipassoc(_dot_)org] On Behalf Of Dave Crocker

1. If the signer publishes support for multiple algorithms, 
then the publisher supports those algorithms.  If they made 
poor choices, that's their problem.

The term 'poor choice' is POV.

What you mean here is 'poor choice from the practical point of view'. The new 
algorithms is almost certainly going to be a better point of view from the 
cryptographic point of view or why change?

So what you are saing is that if someone wants to migrate from SHA-1 to SHA-256 
or the equivalent then that's the problem for the publisher rather than the 
working group charged with engineering a system here.

That's nonsense.


Doing something that causes a signature to fail is something 
I class as a downgrade.

That is not the security area definition of a downgrade attack. A downgrade 
attack is when the attacker gains a more favorable outcome by causing a party 
to accept a lower degree of security than they should expect.

The only purpose of a security policy mechanism is to prevent a downgrade 
attack.

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