Re: [TLS] Adoption call for TLS Flag - Request mTLS

[Jonathan Hoyland <[e-mail]>]

Hi all,

Thanks for the feedback here.

With respect to RFC 7250, as I mentioned earlier on list, there seen to be
two issues. First it changes the semantics of the extension slightly, and
second the RFC explicitly excludes x.509 certs.

IIUC the semantics of the extension are "I have a weird client cert", not
"I have a client cert".

With respect to whether this needs to be a working group item, I'm not
particularly averse to this being an independent document if that's where
the WG thinks it should go.
In my opinion, however, there are two things that it would be good to get
input from the TLS WG on.

One, this is a change from all previous versions of TLS in which the client
cannot induce auth, does enabling this break anyone's assumptions?

Two, I'd like a low flag number because it saves bytes on the wire, but
there is a discussion to be had as to how common this flag will be versus
other flags.
(Non-attack) Bot traffic is very common, but it's not the majority of
traffic by any means.

Regards,

Jonathan



On Thu, 4 Apr 2024, 01:17 Christopher Patton, <cpatton=
[e-mail]> wrote:

> It would be great to here from Jonathan (the author) if RFC 7250 is
> already sufficient for this use case.
>
> On Tue, Apr 2, 2024 at 10:23 PM Mohit Sethi <[e-mail]> wrote:
>
>> Please see my earlier comment regarding this draft:
>> https://mailarchive.ietf.org/arch/msg/tls/g3tImSVXO8AEmPH1UlwRB1c1TLs/
>>
>> In summary: the functionality of this draft is already achievable by
>> using the client_certificate_type extension defined in RFC 7250:
>> https://datatracker.ietf.org/doc/html/rfc7250 with certificate type
>> value = 0:
>>
>> https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values.xhtml#tls-extensiontype-values-3
>> .
>>
>> The table in section 4.2 of RFC8446 even mentions that the extension can
>> be included in the ClientHello:
>> https://datatracker.ietf.org/doc/html/rfc8446#section-4.2, thereby
>> ensuring that the server sends a CertificateRequest message in response
>> to the ClientHello received.
>>
>> OpenSSL already implements this extension since it was needed for
>> support raw public keys (RPKs).
>>
>> As stated earlier: if it is indeed the case that the
>> client_certificate_type extension is suitable for the use-case, then
>> perhaps it is preferable to not have a separate flag. Otherwise, it
>> would make the state machine at the server more complicated (for
>> example: handling a ClientHello with both the mTLS flag and the
>> client_certificate_type extension.
>>
>> Therefore, like Ekr, I am mildly negative on adopting this document but
>> for different reasons.
>>
>> --Mohit
>>
>> On 4/3/24 00:52, Sean Turner wrote:
>> > At the IETF 119 TLS session there was some interest in the mTLS Flag
>> I-D (
>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fdraft-jhoyla-req-mtls-flag%2F&data=05%7C02%7Cmohit.sethi%40aalto.fi%7C42877de6d3d64135e49e08dc534a463b%7Cae1a772440414462a6dc538cb199707e%7C1%7C0%7C638476825681199391%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=ERzWFcuBlAfobNyGCcgKDhCl9wex9LOQ%2F3yPYC7idfU%3D&reserved=0);
>> also, see previous list discussions at [0]. This message is to judge
>> consensus on whether there is sufficient support to adopt this I-D.  If you
>> support adoption and are willing to review and contribute text, please send
>> a message to the list.  If you do not support adoption of this I-D, please
>> send a message to the list and indicate why.  This call will close on 16
>> April 2024.
>> >
>> > Thanks,
>> > Deirdre, Joe, and Sean
>> >
>> > [0]
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