Keyserver doesn't honour signature removal

[David Shaw]

On Apr 21, 2009, at 1:31 AM, Sven Radde wrote:

> Hi!
>
> David Shaw schrieb:
>>> With PKA, you can even get automatic key retrieval without a  
>>> keyserver.
>>
>> That's not quite right.  PKA records in DNS can point to a keyserver,
>> but you still need the keyserver in the mix somewhere (though, like  
>> the
>> "preferred keyserver" feature, that "keyserver" might be a key  
>> stored on
>> a web server).
>
> True, you still need some kind of server (one might argue that even
> using CERT, you have a 'keyserver' - the DNS server itself).
> The notable difference, however, is that a web server presents my key
> exactly as *I* desire, allowing for removed signatures, replacing the
> key by a new one etc.
> PKA is the way to get somebody to use my web server already for  
> initial
> key retrieval (although this might not be the primary purpose of  
> PKA) so
> that the (synchronizing merge-only) keyserver network is avoided.

Absolutely.  I do the same thing, just using CERT.  CERT has two  
modes: "PGP" (where the whole key lives in DNS), and "IPGP" for  
Indirect PGP, where you give a URL as in PKA.  IPGP and PKA are  
basically the same thing from the find-a-key perspective.

It's sort of questionable how practical PGP mode is, with the whole  
key stuffed in to DNS.  You'd get into DNS over TCP fairly quickly,  
and then (poor) firewalls can start being cranky.  GnuPG does support  
getting keys this way, and I suppose it could be useful with a  
stripped down key (no 3rd party signatures, or even the output of  
"minimize") and expect that people will eventually learn the rest of  
the key info from a full keyserver.  I suspect the basic idea is more  
useful for distributing other OpenPGP objects like revocations, as  
they are quite small and the DNS check for a revocation is quite cheap.

IPGP, though, is very handy.

>> CERT is a standardized way (RFC-4398) to put OpenPGP keys in DNS.
>
> Unfortunately, my provider does not allow me to set CERT type DNS
> records. TXT is possible (for, e.g., SPF and PKA).
> I will ask whether they can do it (since it appears to be natively
> supported in BIND 9, right?)

Ugh, that's a problem.  CERT has been supported since mid BIND 8 (and  
arguably longer since you can do stuff like "TYPE37" and raw  
encoding), but if your provider doesn't let you set arbitrary records,  
then you're stuck.  I've seen providers that do DNS through a web GUI  
with a drop-down menu that allows you to choose A, CNAME, or TXT.  I  
suppose we should be grateful they at least allow TXT!

David