I have deleted The GitHub repositories referred to in this post; see Clearing the deck for details.

This post is part of my HOWTO series on Emacs.

There is a tool called ccrypt that uses Rijndael encryption to encrypt and decrypt files. I use this myself to secure my personal journal, and a file containing useful passwords and the like. Normally, I'd use it like this:

$ echo Hello world! > foo.txt
$ ccrypt -e foo.txt
Enter encryption key: pass
Enter encryption key: (repeat) pass
$ cat foo.txt.cpt
��䒨y
u��t4@�6Z?UE�
��[~u50Օ���d����
�
$ ccrypt -d foo.txt.cpt
Enter decryption key: pass
$ cat foo.txt
Hello world!

As you can see, ccrypt -e does the encryption after prompting for a key, renaming foo.txt to foo.txt.cpt in the process. Obviously, ccrypt -d does the decryption. Unfortunately the whole process is a bit convoluted, involving a command prompt and the possibility of forgetting to encrypt the file again afterwards.

Fortunately there's an Emacs plugin for ccrypt that handles all of this for you. Below are instructions on setting this up for Linux and Windows; as usual (nowadays - how things have changed), the Linux installation is quick and easy and the Windows installation awkward.

After the installation instructions, I describe how to use the plugin, and then go on to explain the changes I made to my .emacs file and .emacs.d directory to enable it.

Linux Installation

1. First, install ccrypt with:

   sudo apt-get install ccrypt

2. Next, if you've installed my personal Emacs configuration from GitHub, update it with:
   

   cd ~/duncans_emacs
   git pull

... and you're good to go.

Go and bask in the sun, drink a beer, reflect on how easy that was ... and consider making a donation to the folks who make your Linux Distro (Ubuntu in my case), or the Free Software Foundation who make Emacs.

Windows Installation

1. First, download the Cygwin build of ccrypt from ccrypt-1.7.cygwin-i386.zip.
2. Then, unzip that file into your program files folder, so that you have something like C:\Program Files\ccrypt-1.7.cygwin-i386 containing the following:
   

   AUTHORS
   ccrypt.1
   ccrypt.exe
   ccrypt.html
   ChangeLog
   COPYING
   cygwin1.dll
   cypfaq01.txt
   jka-compr-ccrypt.el
   jka-compr-ccrypt.elc
   NEWS
   README
   README.win

3. Edit your PATH environment variable (instructions for Vista and XP) and add the folder you created in Step 2 above, separating it from the others with a semicolon.
   
   You can test that your new environment variable is set correctly by opening a Command Prompt and typing:
   

   ccrypt --version

   You should see something like:

   ccrypt 1.7. Secure encryption and decryption of files and streams.
   Copyright (C) 2000-2004 Peter Selinger.

   ... in response.

   
   
   
4. Finally, if you've installed my personal Emacs configuration from GitHub, update it with by running Git Bash and entering:
   

   cd ~/duncans_emacs
   git pull
   cd ~
   rm -rf .emacs .emacs.d
   cp -f duncans_emacs/emacs .emacs
   cp -rf duncans_emacs/emacs.d .emacs.d
   

... and don't forget to glare at your Linux-using neighbour who's lazing around outside in the sun at this point :-)

Using It

If you save a buffer with a file extension .cpt, Emacs will automatically prompt you for a key and encrypt the buffer with ccrypt when it saves. If you open a file with the extension .cpt, Emacs will prompt you for a password to decrypt the buffer into memory. That's all there is to it.

If you're a real Emacs newbie and you're sitting there thinking "what does he mean by buffer?" then you should read through the Keyboard Basics section of this excellent Emacs tutorial. All will become clear, I promise ... and if it doesn't, please either post your questions in the comments section, or email me.

Details

In order for Emacs to load the ccrypt plugin we need to do two things in the .emacs file: add the path to the plugin to load-path (the list of paths Emacs checks when instructed to load something), and then actually load the plugin.

This line adds to the path:

(add-to-list 'load-path
             "~/.emacs.d/ccrypt")

And these lines load the plugin (well actually, the first is a comment):

;; allow automagic editing of ccrypt-ed files
(require 'jka-compr-ccrypt "jka-compr-ccrypt.el")