I welcome signed and encrypted mail, although I may take longer to
reply to it because I have not yet implemented decent support for it
in my mail client.  I welcome both OpenPGP and CMS / S/MIME messages.
Here are the relevant files:

. riastradh.pgp (key id BD2D02B0)
  (Key fingerprint: BDC7 C20D 793B 0AEE 7CCA  15A3 0635 0580 BD2D 02B0)

  My current OpenPGP certificate.  This contains only my public key,
  user id, and self-signature packets.  If you want other signatures,
  look for them at a public key server.

. riastradh.pem
  (SHA-1 fingerprint: 520E 30DD 6728 DA77 D598  F87F ECBC 333B D33B BE87)

  My current x.509 certificate from CSAIL.  Unless you are affiliated
  with CSAIL, you probably do not have a root CA certificate with any
  chain to this certificate, so that verifying this one will fail.
  You can find CSAIL's CA certificates at <http://ca.csail.mit.edu/>
  if you want.

. riastradh.pem.p7s

  A signature on my current x.509 certificate created with my last
  (now expired) x.509 certificate.  If you have that x.509 certificate
  in a PEM file named <certificate>, you can verify this one with

    openssl smime -verify -noverify -nointern -inform PEM
      -certfile <certificate> -content riastradh.pem
      -in riastradh.pem.p7s -out /dev/null

  Yes, I really meant to write `-verify -noverify'.  If verification
  succeeds, OpenSSL will proceed to print `Verification successful' to
  standard error (and the content of riastradh.pem to /dev/null).  If
  verification fails, OpenSSL will barf.

These files are mirrored at

<http://mumble.net/~campbell/>
<http://people.csail.mit.edu/riastradh/>