If you're like me, you're occasionally forced to mail some pretty sensitive things around. When that happens, it's not enough to say "Well, I deleted the message." The message is still in your trash, on a server's disk, etc, etc. You need to assume someone WILL get ahold of it and take measures to prevent them from doing anything with it.
My personal favorite (since it can be used in any situation) is the openssl file encryption capability. The openssl package is almost universally installed by default in distros these days, so you should just be able to jump straight to the commands.
In this case, I've got a file called "spreadsheet.xls" that I want to password encrypt. The syntax is simply this:
openssl aes-256-cbc -a -salt -in spreadsheet.xls -out spreadsheet.xls.enc
Then just supply the password you want to use.
And when you want to decrypt it, just add the '-d' switch and flip the filenames:
openssl aes-256-cbc -d -a -in spreadsheet.xls.enc -out spreadsheet.xls
And use your password.
Just like that, you've got munition-grade encryption from the command-line.
Enjoy
