The latest addition to the mutt CVS tree is PKA support via gpgme. While trying to figure out how that works in mutt (I haven't yet...) I configured my DNS server for PKA and CERT records.

PKA

PKA (public key association) puts a pointer where to obtain a key into a TXT record. At the same time that can be used to verify that a key belongs to a mail address. The documentation is at the g10code website (only in German so far). I put the following into the df7cb.de zone:

cb._pka IN TXT "v=pka1;fpr=D224C8B07E63A6946DA32E07C5AF774A58510B5A;uri=finger:cb@df7cb.de"

$ host -t TXT cb.pka.df7cb.de
cb.pka.df7cb.de descriptive text "v=pka1\;fpr=D224C8B07E63A6946DA32E07C5AF774A58510B5A\;uri=finger:cb@df7cb.de"

Now gpg can be told to use PKA to find the key:

$ echo foo | gpg --auto-key-locate pka --recipient cb@df7cb.de --encrypt -a
gpg: no keyserver known (use option --keyserver)
gpg: requesting key 58510B5A from finger:cb@df7cb.de
gpg: key 58510B5A: public key "Christoph Berg cb@df7cb.de" imported
gpg: Total number processed: 1
gpg:               imported: 1
gpg: automatically retrieved `cb@df7cb.de' via PKA

CERT

CERT records work similarly. Records are generated by make-dns-cert (from the tools directory in the gnupg source). cb.gpg is a stripped-down gpg keyring (created with pgp-clean -s and converting from .asc to .gpg).

$ ./make-dns-cert -f D224C8B07E63A6946DA32E07C5AF774A58510B5A -n cb
cb      TYPE37  # 26 0006 0000 00 14 D224C8B07E63A6946DA32E07C5AF774A58510B5A
$ ./make-dns-cert -k cb.gpg -n cb
cb      TYPE37  # 1338 0003 0000 00 9901A20440 [...] 509C96D4BFF17B7

With a new bind and host (backports.org!) the format looks a bit nicer, that's also what I copied into the zone file:

$ host -t CERT cb.df7cb.de
;; Truncated, retrying in TCP mode.
cb.df7cb.de has CERT record PGP 0 0 mQGiBECBGdAR [...] UDlCcltS/8Xtw==
cb.df7cb.de has CERT record 6 0 0 FNIkyLB+Y6aUbaMuB8Wvd0pYUQta

Again, gpg can be told to use that:

$ echo foo | gpg --auto-key-locate cert --recipient cb@df7cb.de --encrypt -a
gpg: key 58510B5A: public key "Christoph Berg cb@df7cb.de" imported
gpg: Total number processed: 1
gpg:               imported: 1
gpg: automatically retrieved `cb@df7cb.de' via DNS CERT

Thanks to weasel for some hints on using CERT.

SSHFP

I'm also mentioning SSHFP records here since it fits in the topic - I have been using them for some months now:

$ host -t SSHFP tesla.df7cb.de
tesla.df7cb.de has SSHFP record 1 1 EE49B803541293656C33B86ECD781BD8F1D78AB5
tesla.df7cb.de has SSHFP record 2 1 3E82FB5EE8AA0205305F0D0186F94D6FB3E0E744
$ ssh -o 'VerifyHostKeyDNS yes' tesla.df7cb.de
The authenticity of host 'tesla.df7cb.de (88.198.227.218)' can't be established.
RSA key fingerprint is 5a:c9:38:ca:c0:2b:11:c1:c8:fb:f1:ad:73:a1:9c:8b.
Matching host key fingerprint found in DNS.
Are you sure you want to continue connecting (yes/no)?

The records are generated with ssh-keygen -r.