CCrypt is in most Linux repos. I use it on Crunchbang Statler (Debian Squeeze) to encrypt and decrypt files quickly with nothing more than two commands and a password.
Firstly install Ccrypt:
sudo apt-get install ccrypt
Now create a test file and add some basic text:(I put encrypt decrypt)
Now encrypt the file (it’ll ask for a password twice):
Now open it and it is unreadable:
To decrypt: use the “-d” switch
ccrypt -d encrypt-test.txt