Re: [Acme] tls-sni-01 validation compromise

Martin Thomson <martin.thomson@gmail.com> Fri, 22 January 2016 04:09 UTC

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Date: Fri, 22 Jan 2016 15:09:25 +1100
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From: Martin Thomson <martin.thomson@gmail.com>
To: Jehiah Czebotar <jehiah@gmail.com>
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Subject: Re: [Acme] tls-sni-01 validation compromise
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Thinking more about this, if the intent is to make the tls-sni-xx
challenge analogous to the http-xx one, then the request would encode
the token (not a hash of the key authorization) and the response to
that challenge would include the key authorization (as I suggest
below).

On 22 January 2016 at 14:03, Martin Thomson <martin.thomson@gmail.com> wrote:
> On 22 January 2016 at 13:38, Jehiah Czebotar <jehiah@gmail.com> wrote:
>> 1) Change the requirement that the self signed cert have one DNSName,
>> and require the response to have TWO DNS names. One that matches the
>> requested hostname, and a second that is secret which proves it can
>> only be created by the appropriate party initiating validation
>> 2) Remove reliance on SNI matching, and make the challenge `tls-01`
>> and fulfill the same HTTP response requirements as `http-01` where the
>> Hostname, and request path are untrusted, but the response body with
>> full keyAuthorization proves the connection to the requestor. This
>> opens up the possibility of TLS validation against the $domain being
>> validated instead of relying on a .acme.invalid hostname.
>
> I think that the suggestion that the challenge response include
> something unique to the challenge (as http-01 already does) is a fine
> suggestion.  I don't think that it matters much how that is done.  If
> the intent is to verify that the requester exercises control over the
> TLS server, having this restricted to things that are part of the TLS
> server configuration is probably advisable.
>
> To that end, adding a key authorization to the certificate would seem
> to be the best option.  Whether that is done as a second
> subjectAltName or as a separate extension probably doesn't matter
> much.
>
> Following through with a challenge like http-01 would work, but it
> means playing with the configuration of the server in two places.