I was looking for a lightweight, transparent encryption solution for
use with emacs that was not dependent on GnuPG, and came across
ccrypt [0]. I think it exemplifies the Unix tradition of doing one
thing well, that being encryption/decryption. It is small and
compiles easily on most Linux and BSD's, and comes with an elisp
interface. I compiled it from source, then copied the
emacs/ps-ccrypt.el and emacs/ps-ccrypt.elc into one of the
directories in my load-path, and added the following to my ~/.emacs:

    (require 'ps-ccrypt "ps-ccrypt.el")

After that, I was able to transparently load, save or edit *.cpt
files in emacs and they were encrypted/decrypted as needed, with the
password prompt shown on initial load or save only. The password
prompt is always shown in the emacs modeline or terminal, unlike
with GnuPG, where newer versions have defaulted to displaying a
popup, graphical password prompt (yuck). The cipher used is
Rijndael, which is used in AES, but ccrypt uses a larger block
size. There are Debian packages available also (ccrypt and
elpa-ps-ccrypt).

[0]: https://ccrypt.sourceforge.net