It is not hard to make Pine read and send GPG-encrypted or -signed messages. Several tools are available that glue gpg and pine together, and I use Pine Privacy Guard (PPG). This is a small Perl script that does all the hard work.

• Install Pine Privacy Guard on your computer:

  wget http://quantumlab.net/pine_privacy_guard/pinepg-1.02.tgz
  tar -C /usr/local -zxvf pinepg-1.02.tgz 
  cd /usr/local/
  chown -R root:root /usr/local/pinepg-1.02
  ln -s pinepg-1.02 pinepg
  chmod 755 /usr/local/pinepg/pine_privacy_guard.pl 

  If you install PPG in another place than /usr/local/pinepg, make certain that you adapt the pathnames that are used further down in the Pine configuration.

• Uncomment the line default-recipient-self in your ~/.gnupg/gpg.conf file to encrypt to self so you can are able read your own encrypted sent messages later on:

  #default-key 0xYourKeyID
  default-recipient-self

• Configure Pine's display-filters and sending-filters
  either edit your ~/.pinerc directly and make sure that the relevant bits look like this:

  # This variable takes a list of programs that message text is piped into
  # after MIME decoding, prior to display.
  display-filters=_LEADING("-----BEGIN PGP MESSAGE-----")_ /usr/local/pinepg/decrypt _RESULTFILE_ _DATAFILE_ _PREPENDKEY_,
          _LEADING("-----BEGIN PGP SIGNED MESSAGE-----")_ /usr/local/pinepg/verify _TMPFILE_ _RESULTFILE_
  
  # This defines a program that message text is piped into before MIME
  # encoding, prior to sending
  sending-filters=/usr/local/pinepg/clearsign _RESULTFILE_ _DATAFILE_ _PREPENDKEY_,
          /usr/local/pinepg/encrypt _RECIPIENTS_ _RESULTFILE_ _DATAFILE_ _PREPENDKEY_

  or configure this from within Pine: (Setup > Config > Whereis > display-filters and add the two values shown above. Same for sending-filters)

• (Optionally - looks cool) add these custom X-Headers to each email you send with pine:

  # Add these customized headers (and possible default values) when composing
  customized-hdrs=X-GPG-PUBLIC_KEY: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xA7
  5CBDA0,
          X-GPG-FINGRPRINT: F2CE 1B92 EE1F 2C0C E97E 581E 5E56 AAAF A75C BDA0

  You can edit ~/.pinerc directly (look for the customized-hdrs= line) or configure from within pine (Setup > Config > Whereis > customized-hdrs)
  Of course, the example GPG fingerprint and key-URL are mine, and you should substitute your own.