truecrypt

TrueCrypt is a software system for establishing and maintaining an on-the-fly-encrypted
volume (data storage device).

On-the-fly encryption means that data is automatically encrypted or decrypted
right before it is loaded or saved, without any user intervention.
No data stored on an encrypted volume can be read (decrypted) without using
the correct password/keyfile(s) or correct encryption keys.

Entire file system is encrypted (i.e., file names, folder names, contents of
every file, and free space).

Reminder: Mount volumes with '-m nokernelcrypto' option if you encounter error like "Error: device-mapper: reload ioctl on truecrypt1 failed: No such file or directory"

Example:

#  truecrypt /root/test.txt /root/encrypted  -m nokernelcrypto

will mount the encrypted file /rootroot.txt in folder /root/encrypted