Truecrypt is a handy cross-platform application to create and use encrypted file containers and disks. What this means is that you can
- create an encrypted file, which acts as a virtual disk (you can mount it) where you can store files
- encrypt a whole physical disk or disk partition on storage device – even USB disk
- encrypt Windows boot partition
This encryption and decryption is transparent when disk is mounted. This means that unmounted disk (and everything stored in it’s filesystem) is unreadable garbage to outsider. He might be able to see that there may be some data, but he cannot read it. When you mount the disk with Truecrypt application and with a proper password/keyfile, the disk can be accessed just like any other unencrypted storage media. When you write something on the disk Truecrypt encrypts it on the fly, and when you read something, that also is decrypted on the fly.
Truecrypt disk is like a box where lid is either open or closed. You cannot open it without proper password, and it is then impossible to access anything that is in the box. When you give the proper password, the lid is opened and you can access anything that is in the box. If you read a file (which is in the box), it stays in the box, but you can read it. Only if you specifically copy or move it out from the box, then it is not encrypted anymore, even if you close the box. If you put something in the box, it is encrypted and will be inaccessible when you close the lid (unmount the disk). That is why it is called a file container.
Encrypted file containers are handy, since you can move them just like any other file. You can even send them as an email attachment. But remember, that you have to format the file container in such a format, that can be used on any platform. If you are using the disk only on one platform, then it does not matter – you can use what ever format makes your fancy.
Installation packages are on Truecrypt website. Be sure to download a package that is appropriate to your operating system and architecture. In Linux you can use both command line and GUI application. Installation is very easy, just follow the included instructions.