How to increase the privacy and the safety of your data on Dropbox

This note is intended mainly for users of a laptop computer to protect their data from the action of thieves.

Privacy

Privacy is the ability to protect your data from being read without your authorization.

A good way to prevent a thief from reading your data is creating an encrypted volume in your Dropbox folder with TrueCrypt, and storing there the data you want to keep secret. See their website for instructions on creating and mounting an encrypted volume.

If you use TrueCrypt, you must unmount the volume before it can be uploaded by Dropbox. You will need to remount (and supply the password again) to view any files in the volume. You should also avoid making changes to the volume on more than one computer at the same time, since Dropbox would be creating a conflicted copy of the entire volume, rather than one single file, if multiple conflicting changes are made at the same time. The security of this approach depends almost entirely on the strength of your passphrase!

On Mac OS X you can also create an encrypted Disk Image (.dmg) using Disk Utility (normally found in /Applications/Utilities). Alternatively, you may encrypt your entire home directory using FileVault (System Preferences -> Security -> FileVault).

Another general (more elegant) solution to an encrypted block device is to use file-by-file encryption. One such solution exists and is called EncFS. This is a plugin for the open source Fuse project for which also a Mac version is available: MacFUSE. The advantages of file-based encryption vs. block-based encryption are related here. Particularly the advantages of this method lends itself very well to the implementation of Dropbox.

Safety

Since Dropbox automatically connects to your account, anyone who can access your user profile (on the OS) is able to access your Dropbox files. They can also access your web interface, so although they cannot lock you out of your own account (Dropbox's password reset needs the current password, which is not compromised), they can inflict significant damage by deleting and purging important files.

The only secure way to prevent this is to encrypt your entire hard drive using something like TrueCrypt, however, these guidelines should be sufficient to protect your computer in your temporary absence.

• disable automatic user login on your computer;

• setting a strong password for your user account;

• make your computer prompt for the user password after waking from screensavers, sleep, or hibernation.

On Windows Vista

Instead of setting a "strong" password which is a pain to remember, it may be more convenient to set a satisfactory password with an account lockout policy. This will, for example, allow 3 incorrect incorrect attempts before denying all login attempts for 15 minutes (12 tries per hour), rendering it virtually impossible for any human to guess the password during your temporary absence.

To do this, run "secpol.msc" then navigate to Security Settings > Account Policies > Account Lockout Policy. Account lockout threshold is the number of incorrect attempts to allow before locking the user. Account lockout duration is the amount of time to maintain the lockout, and Reset account lockout counter after should be the same as Account lockout duration, unless you want some rather interesting effects.

This will, however, be utterly ineffective against erasing the Windows password on boot. Strong passwords are similarly ineffective against such an attack. You can remedy this by disabling booting from removable media in the BIOS. you will also need to set a strong BIOS password to prevent attackers from changing this setting.

The BIOS password is also easily erasable by removing the BIOS battery for a short period, this is extremely easy to do on a desktop, but relatively harder on a laptop. To reiterate a previous point, all of this will only protect your data from your temporary absence. The only way to truly secure your data is to encrypt it. Even disk-wide encryption (on the OS disk, anyways) can be broken into relatively easily compared to encrypted volumes, but it is far more effective than a Windows password.