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

[Jonathan Hoyland <[e-mail]>]

Hi Dennis,

RFC 7250 Section 4.1 says:

If the client has no remaining certificate types to send in
   the client hello, other than the default X.509 type, it MUST omit the
   client_certificate_type extension in the client hello.


That seems to explicitly exclude sending the single entry 0 to me.


Regards,


Jonathan



On Thu, 4 Apr 2024, 16:43 Dennis Jackson, <ietf=
[e-mail]> wrote:

> Hi Jonathan,
>
> My reading of RFC 7250 is the same as Mohits. Although the RFC talks about
> raw public keys and a new codepoint for them, it is building on RFC 6091
> which defined a similar extension and the X509 codepoint.
>
> It seems fine for you to send the client_certificate_type extension with
> the single entry 0 (X509). You also have the option of using a value
> assigned for private use (224 and up) for your specific use case of
> indicating a search engine crawler willing to provide a client cert.
>
> Best,
> Dennis
> On 04/04/2024 11:17, Jonathan Hoyland wrote:
>
> 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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