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Re: [Acme] dns-01 challenge limitations

Michael Richardson <mcr+ietf@sandelman.ca> Fri, 11 September 2020 17:06 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Simon Ser <contact@emersion.fr>
cc: "acme@ietf.org" <acme@ietf.org>, "Matthew.Holt@gmail.com" <Matthew.Holt@gmail.com>
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Date: Fri, 11 Sep 2020 13:06:41 -0400
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Subject: Re: [Acme] dns-01 challenge limitations
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Simon Ser <contact@emersion.fr> wrote:
    > dns-01 requires the ACME client to complete the challenge by updating a DNS
    > record. This is bothersome because this often requires interacting with the
    > DNS registry operator. This is typically done via vendor-specific APIs, with
    > access control handled via vendor-specific means (tokens, public keys,
    > etc).

I guess if you've hosted your zone with the registrar, then that might be
true.  my opinion: Don't do that.

Host your own zone, and/or use Dynamic DNS update (RFC3007), which is mature technology.
There are some annoyances with TSIG until you realize that the key name
really matters.

    > For instance, it would be possible to require users to add a short public key
    > in a DNS TXT record, then ask the ACME client to sign challenges with that key.
    > Something like this would significantly ease the development of ACME
    > clients.

So, this would be be a client key challenge.
This would not be dns-01.  It could certainly work, but it would be a new effort.
Maybe we could use SIG(0), I'm not sure.
The question would be whether or not it would get implemented.

    > Are there specific reasons why dns-01 requires updating a DNS record?

Yes, because it proves you control the zone.

--
Michael Richardson <mcr+IETF@sandelman.ca>   . o O ( IPv6 IøT consulting )
           Sandelman Software Works Inc, Ottawa and Worldwide

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