[TLS] OpSec WGLC for draft-ietf-opsec-ns-impact

Nick Lamb <njl@tlrmx.org> Mon, 17 August 2020 15:39 UTC

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Date: Mon, 17 Aug 2020 16:39:38 +0100
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From: Nick Lamb <njl@tlrmx.org>
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Cc: opsec@ietf.org
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Subject: [TLS] OpSec WGLC for draft-ietf-opsec-ns-impact
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I am not very familiar with IETF working group practices, however it
strikes me as surely unusual to have a document enter Last Call
(supposedly believed by its owners to be ready for publication) and yet
immediately then be revised showing it was in fact not ready at all.

However this seems to be what happened to draft-ietf-opsec-ns-impact.
The below comments concern draft-ietf-opsec-ns-impact-02, the newer
document.

Section 4.1 Perfect Forward Secrecy ends:

> TLS session data.ss

I think this is a typographical error and the trailing "ss" should be
removed from the document. If not it should be explained.



Section 4.2 Encrypted Server Certificate describes a practice which is
inherently unsound. Passive inspection of the Certificate message from
TLS 1.2 or earlier isn't a reliable source of information because a
passive eavesdropper isn't able to discern whether the X.509 document
presented corresponds to this server or not. The Client can confirm
this using the TLS protocol but an eavesdropper can't. So the change in
TLS 1.3 does not impact the practical security policy available, only an
appearance is altered.

Passive systems described throughout Section 5.1 fall to this same
error, using the phrase "reduced effectiveness" which the document
defines as not being "as effective on TLS 1.3 traffic" but in fact
since this practice didn't work, it will remain exactly as effective
(not at all) as before.

A related consequence passes into Section 5.2. Since the Certificate
message is only reliable for a Client, it has in fact always been
necessary to fully proxy the TLS session in order to rely on this data,
so this is not in fact an impact from TLS 1.3 but (if it wasn't done
previously for all versions) a vulnerability in such products.


As it stands then, this document is misleading.

Nick.