Ah, I wonder what the motivation was for it being a MUST rather than a SHOULD.

That still leaves open sending a private use value - which would allow you to de-conflict with others uses.


On 04/04/2024 17:11, Jonathan Hoyland wrote:
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=40dennis-jackson...@dmarc.ietf.org> 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=40cloudflare....@dmarc.ietf.org> 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 <mo...@iki.fi> 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
            
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