to install GPG on FreeBSD:
cd /usr/ports/security/gnupg/ make install clean
Ensure to do this as root. From the install options, select at least CURL.
GNUPG 2.x on FreeBSD by default uses gpg-agent and pinentry for password entry - and for me pinentry was not auto-installed with GPG. To install:
cd /usr/ports/security/pinentry make install clean
Do NOT install pinentry with the default options, unless you want to install a 120Mb X11 package of some description - NCURSES only is fine if you use the FreeBSD machine in terminal mode/text mode/SSH.
gpg --import alice.key
gpg --sign-key Alice
gpg -e -r Alice filename
(where Alice is the userID of the public key to encrypt to, and filename is the name of the file to encrypt)
gpg --verbose --verbose sig.asc
(on Windows, if this is redirected to a tempfile, if the signature does not verify, tempfile will not be created - as yet untested on FreeBSD)
gpg --verify putty.zip.dsa putty.zip
(the public key of the signer must be on the local keyring before the signature can be verified)