Since PGP has a long history and there are a number of PGP implementations available today, the function which each one has differs considerably. For example, if you are using GnuPG, you know you can select cipher algorithm from 3DES, CAST5, BLOWFISH, and so on, but on the other hand the version 2 of PGP only supports IDEA.
Which implementation is used is controlled by the pgg-scheme
variable. If it is nil (the default), the value of the
pgg-default-scheme variable will be used instead.
Force specify the scheme of PGP implementation. The value can be set to
gpg, pgp, and pgp5. The default is nil.
The default scheme of PGP implementation. The value should be one of
gpg, pgp, and pgp5. The default is gpg.