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Re: [TLS] raising ceiling vs. floor (was: New Version Notification for draft-moriarty-tls-oldversions-diediedie-00.txt)

Peter Gutmann <pgut001@cs.auckland.ac.nz> Tue, 10 July 2018 14:17 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: "tls@ietf.org" <tls@ietf.org>
Thread-Topic: [TLS] raising ceiling vs. floor (was: New Version Notification for draft-moriarty-tls-oldversions-diediedie-00.txt)
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Date: Tue, 10 Jul 2018 14:16:57 +0000
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Subject: Re: [TLS] raising ceiling vs. floor (was: New Version Notification for draft-moriarty-tls-oldversions-diediedie-00.txt)
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Viktor Dukhovni <ietf-dane@dukhovni.org> writes:

>also the private CAs using SHA-1 will need to switch to SHA-2 to regain
>interoperability, despite no actual risk from SHA-1.

Another problem with moving to SHA-2 is that when you have a lot of gear that
only does SHA-1, you need to run parallel PKIs possibly in perpetuity, one
using SHA-1 and the other SHA-2.  For example if you're signing CRLs then you
have SHA-2-signed ones and SHA-1-signed ones, and then the CA/signing certs in
turn have to be signed with SHA-1 or SHA-2, and the CA certs for those have to
be SHA-1 or SHA-2, and you can see what a headache that ends up being, not
just in terms of running two PKIs but also the fact that you've now got lots
of apparently duplicated certs that differ only in their hash algorithm.  Or
you can use different keys, but now you also need to change the DNs otherwise
sigs on the SHA-1 branch won't verify on the SHA-2 branch.  No matter how you
look at it, you end up with a mess.

(Luckily this sort of thing is Someone Else's Problem, and I don't envy them
for it).

Peter.

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