The netpgp library is a BSD-licensed library for managing PGP keys.

On top of the library, the netpgp command can digitally sign files and
verify that the signatures attached to files were signed by a given
user identifier.  netpgp can also encrypt files using the public or
private keys of users and, in the same manner, decrypt files which
were encrypted.

The netpgpkeys utility can also be used to generate a new key-pair for
a user.  This key is in two parts, the public key (which can be used
by other people) and a private key.

In addition to these primary uses, the third way of using netpgp is to
maintain keyrings.  Keyrings are collections of public keys belonging
to other users.  By using other means of identification, it is
possible to establish the bona fides of other users.  Once trust has
been established, the public key of the other user will be signed.
The other user's public key can be added to our keyring.  The other
user will add our public key to their keyring.