> On Apr 12, 2017, at 11:59 PM, Phil Pennock <[email protected]>
> wrote:
>
>> I should note that one can of course implement one's SMIMEA deployment
>> in exactly this way, something along the lines of:
>>
>> *._smimecert.example.net. IN SMIMEA 2 1 1
>> e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
>>
>> would associate the same TA public key digest with every user, and would
>> not enable user enumeration.
>
> FWIW, I did something similar to this. Of course, there's a chicken/egg
> problem in _getting_ the CA cert for private CAs, unless you put the
> whole cert into DNS. And wildcards for something that large would be
> cache-unpleasant, but I did the same thing I do for TLSA records: define
> one SMIMEA record and CNAME to it elsewhere. Much more cache friendly.
>
> I never thought I'd see the day that I willingly chose to deploy a
> wildcard CNAME. :^D
>
> $ORIGIN spodhuis.org.
> *._smimecert CNAME _globnix-smimea
> _globnix-smimea SMIMEA ( ; GlobnixCA5 PKIX-less trust anchor
> 02 00 00
> ; SKIP: binary blob for an ECDSA CA
> ; SMIMEA DANE-TA CERT FULL
> )
>
> I can't attest that this _works_. As far as I know, it's entirely
> draft-spec compliant.
Note, that provided your MUA includes the issuing certificate in the
signature block (you can always make it an intermediate CA issued
by a throw-away root whose private key has been destroyed, and then
the MUA should include at least all the intermediates), there's no
need to use "SMIMEA 2 0 0" with the "large" DNS payloads that this
entails. You get the same mileage from "SMIMEA 2 1 1".
That said, ECDSA certificates are often considerably smaller than
is the case with RSA, so "2 0 0" may be sufficient small to avoid
issues with UDP MTUs.
Still, I'd just go with "SMIMEA 2 1 1".
--
Viktor.
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