Re: [Acme] dns-01 challenge limitations

Michael Richardson <> Fri, 11 September 2020 17:06 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id C18033A14CE for <>; Fri, 11 Sep 2020 10:06:48 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -1.899
X-Spam-Status: No, score=-1.899 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id 3X-q2Fts0Xir for <>; Fri, 11 Sep 2020 10:06:47 -0700 (PDT)
Received: from ( []) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 0D8D13A147D for <>; Fri, 11 Sep 2020 10:06:46 -0700 (PDT)
Received: from localhost (localhost []) by (Postfix) with ESMTP id D2B143898F; Fri, 11 Sep 2020 12:45:32 -0400 (EDT)
Received: from ([]) by localhost (localhost []) (amavisd-new, port 10024) with LMTP id kHcnKwZI2UvF; Fri, 11 Sep 2020 12:45:29 -0400 (EDT)
Received: from ( [IPv6:2607:f0b0:f:2::247]) by (Postfix) with ESMTP id 80079389B5; Fri, 11 Sep 2020 12:45:29 -0400 (EDT)
Received: from localhost (localhost [IPv6:::1]) by (Postfix) with ESMTP id EF94575; Fri, 11 Sep 2020 13:06:41 -0400 (EDT)
From: Michael Richardson <>
To: Simon Ser <>
cc: "" <>, "" <>
In-Reply-To: <>
References: <>
X-Mailer: MH-E 8.6+git; nmh 1.7+dev; GNU Emacs 26.1
X-Face: $\n1pF)h^`}$H>Hk{L"x@)JS7<%Az}5RyS@k9X%29-lHB$Ti.V>2bi.~ehC0; <'$9xN5Ub# z!G,p`nR&p7Fz@^UXIn156S8.~^@MJ*mMsD7=QFeq%AL4m<nPbLgmtKK-5dC@#:k
MIME-Version: 1.0
Content-Type: multipart/signed; boundary="=-=-="; micalg="pgp-sha512"; protocol="application/pgp-signature"
Date: Fri, 11 Sep 2020 13:06:41 -0400
Message-ID: <28079.1599844001@localhost>
Archived-At: <>
Subject: Re: [Acme] dns-01 challenge limitations
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Automated Certificate Management Environment <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Fri, 11 Sep 2020 17:06:49 -0000

Simon Ser <> 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 <>   . o O ( IPv6 IøT consulting )
           Sandelman Software Works Inc, Ottawa and Worldwide