Re: [dnssd] [dnssd-wg/draft-ietf-dnssd-srp] possible non-compliant KEY RR flags field used for example in Appendix C (Issue #24)

[Ted Lemon <[e-mail]>]

Alexander Clouter identified in a recent github issue on
draft-ietf-dnssd-srp that our support for the KEY RR looks like it's based
on RFC2535, but RFC2535 was updated by RFC3445. Unfortunately RFC3445
doesn't explicitly update RFC2931, so we missed this. However, the change
is, I think, purely editorial, so should be fine to do at this stage. I've
updated the example Alexander cites to change the flags value from 513 to
0, and added text in the requestor and registrar sections of
draft-ietf-dnssd-srp pointing to RFC3445's requirement for setting the
flags to 0 (requestor) and not checking the flags (registrar).

On Sun, Mar 3, 2024 at 5:44 AM Alexander Clouter <[e-mail]>
wrote:

> Highlighted on the mailing list
> <https://mailarchive.ietf.org/arch/msg/dnssd/tGLWlkxs-6-IWQv6P8h3cMMGOgE/>,
> RFC3445 section 4 <https://www.rfc-editor.org/rfc/rfc3445.html#section-4>
> states that most of the 'flags' field for the KEY RR should be zero.
>
> The example in Appendix C does not adhere to this (flags is 513):
>
> demo               KEY 513 3 13 (
>                            qweEmaaq0FAWok5//ftuQtZgiZoiFSUsm0srWREdywQU
>                            9dpvtOhrdKWUuPT3uEFF5TZU6B4q1z1I662GdaUwqg==
>                         ); alg = ECDSAP256SHA256 ; key id = 15008
>
> It would be helpful to provide advice on what flags value to use
> <https://mailarchive.ietf.org/arch/msg/dnssd/RXUiWIRiz71pRmtyeTw3_VEBFcY/>,
> the only implementations I am aware of to glean hints from also look to be
> non-RFC3445 compliant:
>
>    - mdnsresponder
>    <https://github.com/Abhayakara/mdnsresponder/blob/d7779d704ef6e4724d0d0fd4a11a91ff9caa4004/ServiceRegistration/towire.c#L410>
>    - openthread
>    <https://github.com/openthread/openthread/blob/41526d5de27d451179276dff082eeb138e839445/src/core/net/srp_client.cpp#L1372-L1373>
>
> My reading of both RFC2535 section 3.1.2
> <https://www.rfc-editor.org/rfc/rfc2535#section-3.1.2> and RFC3445
> section 4 <https://www.rfc-editor.org/rfc/rfc3445.html#section-4>, I
> think the flags field should now be simply zero, someone needs to check
> my homework though...
>
> The original KEY RR flags:
>
>    0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
>    +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
>    |  A/C  | Z | XT| Z | Z | NAMTYP| Z | Z | Z | Z |      SIG      |
>    +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
>
> The new KEY RR flags:
>
>    0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
>    +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
>    | Z | Z | Z | Z | Z | Z | Z | N | Z | Z | Z | Z | Z | Z | Z | Z |
>    +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
>
> Where the 'zone bit' (N, bit 7) is for this use case (SIG(0)) is zero (0).
>
> —
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