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Disk encryption is a technology which protects information by converting it into unreadable code that cannot be deciphered easily by unauthorized people. Disk encryption uses disk encryption software or hardware to encrypt every bit of data that goes on a
disk Disk or disc may refer to: * Disk (mathematics), a geometric shape * Disk storage Music * Disc (band), an American experimental music band * ''Disk'' (album), a 1995 EP by Moby Other uses * Disk (functional analysis), a subset of a vector sp ...
or disk volume. It is used to prevent unauthorized access to data storage. The expression ''full disk encryption (FDE)'' (or ''whole disk encryption'') signifies that everything on the disk is encrypted, but the
master boot record A master boot record (MBR) is a special type of boot sector at the very beginning of partitioned computer mass storage devices like fixed disks or removable drives intended for use with IBM PC-compatible systems and beyond. The concept of MBR ...
(MBR), or similar area of a bootable disk, with code that starts the operating system loading sequence, is not encrypted. Some hardware-based full disk encryption systems can truly encrypt an entire boot disk, including the MBR.


Transparent encryption

Transparent encryption, also known as real-time encryption and on-the-fly encryption (OTFE), is a method used by some disk encryption software. "Transparent" refers to the fact that data is automatically encrypted or decrypted as it is loaded or saved. With transparent encryption, the files are accessible immediately after the
key Key or The Key may refer to: Common meanings * Key (cryptography), a piece of information that controls the operation of a cryptography algorithm * Key (lock), device used to control access to places or facilities restricted by a lock * Key (map ...
is provided, and the entire volume is typically mounted as if it were a physical drive, making the files just as accessible as any unencrypted ones. No data stored on an encrypted volume can be read (decrypted) without using the correct password/ keyfile(s) or correct encryption keys. The entire
file system In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...
within the volume is encrypted (including file names, folder names, file contents, and other
meta-data Metadata is "data that provides information about other data", but not the content of the data, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive metadata – the descriptive ...
). To be transparent to the end-user, transparent encryption usually requires the use of
device driver In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabling operating systems and ot ...
s to enable the encryption process. Although
administrator Administrator or admin may refer to: Job roles Computing and internet * Database administrator, a person who is responsible for the environmental aspects of a database * Forum administrator, one who oversees discussions on an Internet forum * N ...
access rights are normally required to install such drivers, encrypted volumes can typically be used by normal users without these rights. In general, every method in which data is seamlessly encrypted on write and decrypted on read, in such a way that the user and/or application software remains unaware of the process, can be called transparent encryption.


Disk encryption vs. filesystem-level encryption

Disk encryption does not replace file encryption in all situations. Disk encryption is sometimes used in conjunction with filesystem-level encryption with the intention of providing a more secure implementation. Since disk encryption generally uses the same key for encrypting the whole drive, all of the data can be decrypted when the system runs. However, some disk encryption solutions use multiple keys for encrypting different volumes. If an attacker gains access to the computer at run-time, the attacker has access to all files. Conventional file and folder encryption instead allows different keys for different portions of the disk. Thus an attacker cannot extract information from still-encrypted files and folders. Unlike disk encryption, filesystem-level encryption does not typically encrypt filesystem metadata, such as the directory structure, file names, modification timestamps or sizes.


Disk encryption and Trusted Platform Module

Trusted Platform Module (TPM) is a secure cryptoprocessor embedded in the
motherboard A motherboard (also called mainboard, main circuit board, mb, mboard, backplane board, base board, system board, logic board (only in Apple computers) or mobo) is the main printed circuit board (PCB) in general-purpose computers and other expand ...
that can be used to authenticate a hardware device. Since each TPM chip is unique to a particular device, it is capable of performing platform authentication. It can be used to verify that the system seeking the access is the expected system. A limited number of disk encryption solutions have support for TPM. These implementations can wrap the decryption key using the TPM, thus tying the hard disk drive (HDD) to a particular device. If the HDD is removed from that particular device and placed in another, the decryption process will fail. Recovery is possible with the decryption password or
token Token may refer to: Arts, entertainment, and media * Token, a game piece or counter, used in some games * The Tokens, a vocal music group * Tolkien Black, a recurring character on the animated television series ''South Park,'' formerly known as ...
. Although this has the advantage that the disk cannot be removed from the device, it might create a single point of failure in the encryption. For example, if something happens to the TPM or the
motherboard A motherboard (also called mainboard, main circuit board, mb, mboard, backplane board, base board, system board, logic board (only in Apple computers) or mobo) is the main printed circuit board (PCB) in general-purpose computers and other expand ...
, a user would not be able to access the data by connecting the hard drive to another computer, unless that user has a separate recovery key.


Implementations

There are multiple tools available in the market that allow for disk encryption. However, they vary greatly in features and security. They are divided into three main categories: software-based, hardware-based within the storage device, and hardware-based elsewhere (such as
CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ...
or host bus adaptor). Hardware-based full disk encryption within the storage device are called self-encrypting drives and have no impact on performance whatsoever. Furthermore, the media-encryption key never leaves the device itself and is therefore not available to any virus in the operating system. The Trusted Computing Group
Opal Storage Specification The Opal Storage Specification is a set of specifications for features of data storage devices (such as hard disk drives and solid state drives) that enhance their security. For example, it defines a way of encrypting the stored data so that an u ...
provides industry accepted standardization for self-encrypting drives. External hardware is considerably faster than the software-based solutions, although CPU versions may still have a performance impact, and the media encryption keys are not as well protected. All solutions for the boot drive require a
pre-boot authentication Pre-boot authentication (PBA) or power-on authentication (POA) serves as an extension of the BIOS, UEFI or boot firmware and guarantees a secure, tamper-proof environment external to the operating system as a trusted authentication layer. The PB ...
component which is available for all types of solutions from a number of vendors. It is important in all cases that the authentication credentials are usually a major potential weakness since the
symmetric cryptography Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both the encryption of plaintext and the decryption of ciphertext. The keys may be identical, or there may be a simple transformation to go between th ...
is usually strong.


Password/data recovery mechanism

Secure and safe recovery mechanisms are essential to the large-scale deployment of any disk encryption solutions in an enterprise. The solution must provide an easy but secure way to recover passwords (most importantly data) in case the user leaves the company without notice or forgets the password.


Challenge–response password recovery mechanism

Challenge–response password recovery mechanism allows the password to be recovered in a secure manner. It is offered by a limited number of disk encryption solutions. Some benefits of challenge–response password recovery: # No need for the user to carry a disc with recovery encryption key. # No secret data is exchanged during the recovery process. # No information can be sniffed. # Does not require a network connection, i.e. it works for users that are at a remote location.


Emergency recovery information (ERI)-file password recovery mechanism

An emergency recovery information (ERI) file provides an alternative for recovery if a challenge–response mechanism is unfeasible due to the cost of helpdesk operatives for small companies or implementation challenges. Some benefits of ERI-file recovery: # Small companies can use it without implementation difficulties. # No secret data is exchanged during the recovery process. # No information can be sniffed. # Does not require a network connection, i.e. it works for users that are at a remote location.


Security concerns

Most full disk encryption schemes are vulnerable to a cold boot attack, whereby encryption
keys Key or The Key may refer to: Common meanings * Key (cryptography), a piece of information that controls the operation of a cryptography algorithm * Key (lock), device used to control access to places or facilities restricted by a lock * Key (map ...
can be stolen by cold-booting a machine already running an operating system, then dumping the contents of memory before the data disappears. The attack relies on the data remanence property of computer memory, whereby data bits can take up to several minutes to degrade after power has been removed. Even a Trusted Platform Module (TPM) is not effective against the attack, as the operating system needs to hold the decryption keys in memory in order to access the disk. Full disk encryption is also vulnerable when a computer is stolen when suspended. As wake-up does not involve a
BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...
boot sequence, it typically does not ask for the FDE password. Hibernation, in contrast goes via a BIOS boot sequence, and is safe. All software-based encryption systems are vulnerable to various side channel attacks such as acoustic cryptanalysis and hardware keyloggers. In contrast, self-encrypting drives are not vulnerable to these attacks since the hardware encryption key never leaves the disk controller. Also, most of full disk encryption schemes don't protect from data tampering (or silent data corruption, i.e. bitrot). That means they only provide privacy, but not integrity. Block cipher-based encryption modes used for full disk encryption are not authenticated encryption themselves because of concerns of the storage overhead needed for authentication tags. Thus, if tampering would be done to data on the disk, the data would be decrypted to garbled random data when read and hopefully errors may be indicated depending on which data is tampered with (for the case of OS metadata – by the file system; and for the case of file data – by the corresponding program that would process the file). One of the ways to mitigate these concerns, is to use file systems with full data integrity checks via checksums (like Btrfs or
ZFS ZFS (previously: Zettabyte File System) is a file system with volume management capabilities. It began as part of the Sun Microsystems Solaris operating system in 2001. Large parts of Solaris – including ZFS – were published under an open ...
) on top of full disk encryption. However, cryptsetup started experimentally to support authenticated encryption


Full disk encryption


Benefits

Full disk encryption has several benefits compared to regular file or folder encryption, or encrypted vaults. The following are some benefits of disk encryption: # Nearly everything including the
swap space In computer operating systems, memory paging is a memory management scheme by which a computer stores and retrieves data from secondary storage for use in main memory. In this scheme, the operating system retrieves data from secondary storage ...
and the
temporary file A temporary file is a file created to store information temporarily, either for a program's intermediate use or for transfer to a permanent file when complete. It may be created by computer programs for a variety of purposes, such as when a program ...
s is encrypted. Encrypting these files is important, as they can reveal important confidential data. With a software implementation, the bootstrapping code cannot be encrypted however. For example, BitLocker Drive Encryption leaves an unencrypted volume to
boot A boot is a type of footwear. Most boots mainly cover the foot and the ankle, while some also cover some part of the lower calf. Some boots extend up the leg, sometimes as far as the knee or even the hip. Most boots have a heel that is cle ...
from, while the volume containing the operating system is fully encrypted. # With full disk encryption, the decision of which individual files to encrypt is not left up to users' discretion. This is important for situations in which users might not want or might forget to encrypt sensitive files. # Immediate data destruction, such as simply destroying the cryptographic keys ( crypto-shredding), renders the contained data useless. However, if security towards future attacks is a concern,
purging A purge is the forcible removal of undesirable people from political activity, etc. Purge or The Purge may also refer to: * Purge (occupied Japan), the forcible removal of undesirable Japanese from public service during occupation of Japan * G ...
or physical destruction is advised.


The boot key problem

One issue to address in full disk encryption is that the blocks where the operating system is stored must be decrypted before the OS can boot, meaning that the key has to be available before there is a user interface to ask for a password. Most Full Disk Encryption solutions utilize
Pre-Boot Authentication Pre-boot authentication (PBA) or power-on authentication (POA) serves as an extension of the BIOS, UEFI or boot firmware and guarantees a secure, tamper-proof environment external to the operating system as a trusted authentication layer. The PB ...
by loading a small, highly secure operating system which is strictly locked down and hashed versus system variables to check for the integrity of the Pre-Boot kernel. Some implementations such as BitLocker Drive Encryption can make use of hardware such as a Trusted Platform Module to ensure the integrity of the boot environment, and thereby frustrate attacks that target the boot loader by replacing it with a modified version. This ensures that authentication can take place in a controlled environment without the possibility of a bootkit being used to subvert the pre-boot decryption. With a
pre-boot authentication Pre-boot authentication (PBA) or power-on authentication (POA) serves as an extension of the BIOS, UEFI or boot firmware and guarantees a secure, tamper-proof environment external to the operating system as a trusted authentication layer. The PB ...
environment, the key used to encrypt the data is not decrypted until an external key is input into the system. Solutions for storing the external key include: * Username / password * Using a smartcard in combination with a PIN * Using a
biometric authentication Biometrics are body measurements and calculations related to human characteristics. Biometric authentication (or realistic authentication) is used in computer science as a form of identification and access control. It is also used to identify in ...
method such as a fingerprint * Using a
dongle A dongle is a small piece of computer hardware that connects to a port on another device to provide it with additional functionality, or enable a pass-through to such a device that adds functionality. In computing, the term was initially synonym ...
to store the key, assuming that the user will not allow the dongle to be stolen with the laptop or that the dongle is encrypted as well * Using a boot-time driver that can ask for a password from the user * Using a network interchange to recover the key, for instance as part of a
PXE PXE may refer to: * Preboot Execution Environment, booting computers via a network * Proof and Experimental Establishment, an Indian defense laboratory * Pseudoxanthoma elasticum, a genetic disease * Pentium Extreme Edition, a variant of Pentium D ...
boot * Using a TPM to store the decryption key, preventing unauthorized access of the decryption key or subversion of the boot loader * Using a combination of the above All these possibilities have varying degrees of security; however, most are better than an unencrypted disk.


See also

* Comparison of disk encryption software * Digital forensics *
Disk encryption hardware Hardware-based full disk encryption (FDE) is available from many hard disk drive (HDD/ SSD) vendors, including: ClevX, Hitachi, Integral Memory, iStorage Limited, Micron, Seagate Technology, Samsung, Toshiba, Viasat UK, Western Digital. The ...
* Disk encryption software * Disk encryption theory * Encryption * Filesystem-level encryption * Hardware-based full disk encryption *'' In re Boucher'' * Single sign-on


References


Further reading

*{{cite journal , last=Casey , first=Eoghan , author2=Stellatos, Gerasimos J. , year=2008 , title=The impact of full disk encryption on digital forensics , journal=Operating Systems Review , volume=42 , issue=3 , pages=93–98 , doi=10.1145/1368506.1368519 , s2cid=5793873


External links


Presidential Mandate requiring data encryption on US government agency laptops

On-The-Fly Encryption: A Comparison
– Reviews and lists the different features of disk encryption systems (archived version from January 2013)

– covers the use of dm-crypt/LUKS on Linux, starting with theory and ending with many practical examples about its usage (archived version from September 2015).

– Overview of full-disk encryption, how it works, and how it differs from file-level encryption, plus an overview of leading full-disk encryption software.