Re: [TLS] Adoption call for draft-davidben-tls13-pkcs1

Hubert Kario <hkario@redhat.com> Thu, 12 December 2019 11:51 UTC

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From: Hubert Kario <hkario@redhat.com>
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Date: Thu, 12 Dec 2019 12:51:24 +0100
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Subject: Re: [TLS] Adoption call for draft-davidben-tls13-pkcs1
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On Wednesday, 11 December 2019 18:06:19 CET, David Benjamin wrote:
> On Wed, Dec 11, 2019 at 9:22 AM Ilari Liusvaara <ilariliusvaara@welho.com>
> wrote:
>
>> On Wed, Dec 11, 2019 at 02:21:48PM +0100, Hubert Kario wrote:
>>> On Saturday, 7 December 2019 11:20:17 CET, Ilari Liusvaara wrote:
>>>> 
>>>> One test I just tried:
>>>> 
>>>> - Smartcard capable of raw RSA.
>>>> - OpenSC PKCS#11 drivers.
>>>> - Firefox ESR 68
>>>> - Server supports TLS 1.3 (Accept RSA PKCS#1v1.5 client signatures is
>>>>   enabled[2]).
>>>> 
>>>> Result: Failed. Client hits internal error code
>>>> SEC_ERROR_LIBRARY_FAILURE
>>>> [3].
>>> 
>>> That doesn't match my understanding of how NSS works – AFAIK, NSS (and as
>>> such, Firefox), will try both raw RSA and rsa-pss signatures with the
>>> token,
>>> depending on what kind of algorithms the token advertises.
>>> 
>>> I think the issue was the old version of OpenSC, new versions can do
>>> rsa-pss
>>> with rsa-raw:
>>> https://bugzilla.redhat.com/show_bug.cgi?id=1595626
>>> https://github.com/OpenSC/OpenSC/pull/1435
>> 
>> Ok, upgrading the OpenSC to git master (0.20.0-rc34-2-gee78b0b8) makes
>> client certificates in TLS 1.3 in Firefox work with that card (works even
>> if accept RSA PKCS#1v1.5 client signatures is disabled on server side).
>> 
>> There is apparently no release with the fix. One needs 0.20-rcX or recent
>> git master.
>> 
>
> Chrome likewise tries to polyfill PSS support out of raw RSA when the
> underlying keys support it, but PSS support is still a problem. In
> particular, I believe TPM 1.2 can neither do RSA-PSS nor polyfill it with
> raw padding. (Oddly, the spec does reference OAEP, but signing is only
> PKCS#1 v1.5.) TPM 2.0 can do PSS, but hardware lifecycles are long. Between
> the negotiation ordering and the client certificate privacy flaw fixed in
> TLS 1.3, simply saying "no TLS 1.3 for those keys" is problematic. Thus,
> the draft. It's true that it adds some transitionary codepoints to TLS 1.3,
> but the point of TLS 1.3 was not switching to PSS. That's a minor bonus on
> top of *much* more important changes.
>
> Most properties negotiated by TLS can be unilaterally updated by the
> TLS-related components of a system. This is great because it means we can
> deploy TLS 1.3's improvements. The long-term credentials are one of the big
> exceptions here and, indeed, we didn't just make TLS 1.3 mandate Ed25519.
> We wanted to maintain continuity with existing RSA keys, but since it was
> possible to switch them to RSA-PSS we went ahead and did that. Sadly, it
> appears that last point can be more true for server keys than client keys.
> :-(

If TLS 1.2 was looking insecure, I would be with you on this one. But given
that TLS 1.2 can be configured to be as secure as TLS 1.3, I think 
introducing
weak points to TLS 1.3, weak points we will have to live with for the next
decade, if not two, is counter-productive and will only delay deployemnt of 
RSA-PSS capable HSMs. Not allowing PKCS#1 v1.5 in TLS 1.3 puts actual 
pressure
to replace that obsolete hardware, without exposing users to unnecessary 
risk.
-- 
Regards,
Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purkyňova 115, 612 00  Brno, Czech Republic