Encrypted Watermarks and Linux Laptop Security

The most common way to implement full-disk encryption (as opposed to encrypted file systems) in the GNU/Linux operating system is using the encrypted loop device, known as CryptoLoop. We demonstrate clear weaknesses in the current CBC-based implementation of CryptoLoop, perhaps the most surprising being a very simple attack which allows specially watermarked files to be identified on an encrypted hard disk without knowledge of the secret encryption key. We take a look into the practical problems of securely booting, authenticating, and keying full-disk encryption. We propose simple improvements to the current CryptoLoop implementation based on the notions of tweakable encryption algorithms and enciphering modes. We also discuss sector-level authentication codes. The new methods have been implemented as a set of patches to the Linux Kernel series 2.6 and the relevant system tools.

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