CFS Howto

(How to use cryptographic file systems)

© (2004) Pablo Arés, pablo /at/ math.tifr.res.in

Basics on cfs

The idea of cfs (Cryptographic Filesystem) is to have an utility that allows the user to save files in an encrypted way, to protect it from being read/modified by other users. The setting of permissions of a file can prevent other "regular" users from reading (modifying) your files, but that is no prevention against the superuser (root). Or in case some one can guess your password, or some other security breach. So, cfs allows you to encrypt files with some other key (it could be your password, but for obvious reasons you should choose another key).
Below you will find the basic way cfs works.

Using cfs

First you will have to create the directory where you will store the files. Let's say you call it crypt-dir. This directory is not made in the regular way, but with the following command:
```
   cmkdir crypt-dir
```
You will be asked for a key; enter something long (but easy to remember).
Now, to create/write files in that directory, you will have to make it available to the cfs system. Choose some name that is likely to be unique, for example username-number, where username is your logging name, and number is a random number. For example, you co do
```
   cattach crypt-dir pablo-3897123
```
The directory is now available for working on it, as a regular directory. You change to it with the following command:
```
   cd /var/cfs/pablo-3897123
```
and work in it as you do in any other directory.
When you finish storing whatever files you want, you will have to "get out" of that directory and save it in encrypted way. Here is what you need to do
```
   cd
   cdetach pablo-3897123
```

Now your files are save in your crypt-dir in an encrypted way. Follow the steps above (cattach and cdetach) to work again in the directory.

Warnings

If you forget your key, there is no way you can recover your files (unless you break the encrpytion, which is not so easy). Not even the superuser will be able to get them (remember, cfs also protect your files from the superuser!).