Daily Archives: 2012-04-05

Three Paper Thursday: full disk encryption

Information is often an important asset and today’s information is commonly stored as digital data (bytes). We store this data in our computers local hard disks and in our laptops disks. Many organisations wish to keep the data stored in their computers and laptops confidential. Therefore a natural desire is that a stolen disk or laptop should not be readable by an external person (an attacker in general terms). For this reason we use encryption.

A hard disk is commonly logically organised in multiple sections, often referred to as either partitions or volumes. These volumes can be used for various purposes, and they are often structured according to a file system format (e.g. NTFS, FAT, HFS, etc.). It is possible to have a single disk with 3 volumes, where the first volume is formatted with NTFS and contains a Windows operating system, the second volume is formatted with EXT3 file system and contains an installation of a Linux distribution, while the third volume is formatted with FAT file system and only contains data (no operating system).

Volume encryption is a mechanism used to encrypt the contents of an entire volume. This is sometimes referred as “full disk encryption”, which is misleading, since a physical disk can actually contain multiple volumes, each encrypted independently.  However, since the term has become very popular, I will continue to refer to this kind of encryption as “full disk encryption” but the reader should keep the above distinction in mind.

There are several products that offer full disk encryption, e.g. PGP Whole Disk Encryption, TrueCrypt, Sophos SafeGuard, or Check Point FDE. Bitlocker is the full disk encryption integrated with the Windows OS and Apple has recently introduced FileVault 2 as full disk encryption from MAC OS X 10.7.

There are several limitations that affect the encryption of an entire disk. These have to do with 3 important aspects among others: a) encryption must be fast (a user should not notice any extra latency); b) the operating system is encrypted as well (so there must be some way of bootstrapping the decryption process when the computer boots)  c) the encryption mechanism should not reduce the available storage space noticeable (that is, we cannot use an extra block of data for every few encrypted blocks).

The following 3 papers explain in detail these limitations. Two of them relate to currently deployed full disk encryption systems.

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