Subject: [dmarc-ietf] SHA1 and short keys, threat or menace

From: "John Levine" <[email-masked]>
Date: 13 Dec 2017 14:10:53 -0500

I am working on yet another ARC library and am wondering what to do
about SHA1 signatures and 512 bit keys.  The DCRUP working group has
sent a DKIM update to the RFC editor which finally kills SHA1 hashes
and RSA keys shorter than 1024 bits.  It's in the queue and will be
published when they get around to it, probably next month.

On the assumption that ARC signatures track DKIM, what should I do?
At the moment I have a "strict" option in the verifier which when set
rejects SHA1 hashes and short keys.  I suppose it should be on by
default, but a couple of the tests in the YANG test suite have SHA1
signatures.  There's also a test that 512 bit signatures are rejected,
so depending on the setting currently I can either fail the SHA1
signatures or I can fail the short key signature.

Suggestions?

Signed,
Uncertain

PS: Coming soon to DKIM, ed25519 signatures, but since the underlying
library code isn't in OpenSSL yet, I'm not yet worrying about it.

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From: "Peter M. Goldstein" <[email-masked]>
Date: Wed, 13 Dec 2017 11:37:10 -0800

So my thought here is that now that DCRUP is due imminently, we should
update the YANG test suite to reject SHA-1 hashes.

Thoughts?

Best,

Peter

On Wed, Dec 13, 2017 at 11:10 AM, John Levine <[email-masked]> wrote:

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From: "John R Levine" <[email-masked]>
Date: 13 Dec 2017 14:40:54 -0500

> update the YANG test suite to reject SHA-1 hashes.

That's what I would do.  Given how new ARC is and the absence of legacy 
code, I don't see any reason to allow them.

R's,
John

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From: "Kurt Andersen (b)" <[email-masked]>
Date: Wed, 13 Dec 2017 19:55:42 +0000

> code, I don't see any reason to allow them.

I agree too. We had that debate about forcing the DCRUP "upleveling" by
writing it into the ARC spec but solved that problem by doing DCRUP
instead. No need to keep legacy support.

--Kurt

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From: "Peter M. Goldstein" <[email-masked]>
Date: Wed, 13 Dec 2017 11:57:52 -0800

Great.  If there's group consensus I can take updating the test suite as an
action item.  Any objections?

Thanks.

Best,

Peter

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From: "Kurt Andersen (b)" <[email-masked]>
Date: Wed, 13 Dec 2017 20:06:16 +0000

On Wed, Dec 13, 2017 at 7:57 PM, Peter M. Goldstein <
[email-masked]> wrote:

> Great.  If there's group consensus I can take updating the test suite as
> an action item.  Any objections?
>

Make it so :-)