Things to Know About Full Disk Encryption

You can encrypt only a few files or your entire computer if you want to store files on your local computer safely. The word “full disk encryption” refers to encrypting everything on the hard drive. Encrypting your files one by one is both more difficult and less secure than using full disk encryption.

If you encrypt your files one by one, your computer may create temporary unencrypted copies of these files without your knowledge. Also, some software may keep some unencrypted records about what you do on your computer. Apple OS X, Linux, and newer versions of Windows all come with the full disk encryption feature, but this feature is generally not used by default.

What is Full Disk Encryption?

Full disk encryption is encoding data placed on a disk, including programs that encrypt partitions in operating systems. Some computer users use partitions as a way of partitioning a hard drive’s storage space.

Encryption scrambles the contents of a message or file so that only those with access to the encryption key can read and decode it. The purpose of encrypting data is to prevent unwanted users from accessing data stored on computer drives. Full disk encryption encrypts operating system files and temporary files or all files on the encrypted disk.

See Also: How do I Protect the Stored Payment Cardholder Data?

Because full disk encryption is usually software-based, it excludes the master boot record, usually the first subsection of the hard disk. The master boot record can also be encrypted if hardware-based full disk encryption is used.

Hardware-based disk encryption creates and stores encryption keys and user information in the drive hardware; therefore, this information is kept independent of the operating system and software. This provides greater security against potential threats from attackers who might gain access to the computer memory. Hardware-based encryption is also useful because it can be opened indefinitely, meaning the user does not have to remember to turn it on when needed.

FIPS 140-2 and Common Criteria EAL4 are two security certificates available for software that offers complete disk encryption. The Federal Information Processing Standard, or FIPS 140-2, is a United States government-accredited security standard for applications that use encryption. The Universal Standards EAL4 standard, on the other hand, is an international standard for computer security.

See Also: How can you make unreadable stored PAN information?

For all of their ability to manage security threats, many full disk encryption programs can be attacked with a cold boot attack. In this case, by turning the computer off and on, the encryption keys are stolen and restarts the computer without the proper shutdown procedure. When the memory information or DRAM is thrown into a file, the intruder will access the information.

How Does Full Disk Encryption Work?

Disk encryption is a method of protecting data through translating it into an unreadable code that is difficult to decode by unauthorized individuals. Disk encryption encrypts any bit that passes through a disk or disk volume using disk encryption software or hardware. It is an excellent method to prevent unauthorized access to data storage.

The statements indicate that full disk encryption (FDE) or encryption of the entire disk, everything on the disk is encrypted. Still, the primary boot record (MBR) or similar bootable disk area with code that starts the system, called the operating system boot loader, is not encrypted.

See Also: What Are the PCI DSS Encryption Requirements

Some hardware-based full disk encryption systems can encrypt the entire disk, including MBR. Many software operates in a structure where data is automatically encrypted or decrypted when loaded or saved.

Full disk encryption (FDE) works at a very low level. It is under the file system, which means it is compatible with every file system. It uses an asymmetric encryption algorithm that works on blocks of data. These blocks are automatically encrypted when written and automatically decrypted when requested. The program typically keeps the key in memory.

A typical choice is a 128-bit block size, 256-bit keyed AES block cipher and CBC operating mode. Block ciphers operate on exact size blocks. They take this size as input and give the same size in the output. The operating mode is the rule applied to deal with other block sizes. The simplest model is ECB (electronic codebook).

ECB mode divides the plain text into blocks of the desired size, fills the last message with zeros, and independently applies the password to each block. This is a bad idea as it clearly shows the repetitive patterns.

To encrypt data, the key must be stored on the device. This means the key must be secure. Besides, the key cannot be stored in the machine in plain text, and the key must be prevented from being forced into rough.

What the user memorizes is the password. This password is operated through an encryption hash function to generate the key. Cryptographic processing means it is computationally heavy, as it has to do that calculation every time you unlock your computer.

However, the attacker must also do this. A typical key derivation function is PBKDF2, and a standard cryptographic hash function is SHA-512. Once the key is derived, it is stored securely in memory.

Instead of using a password, you can also give your users a physical token. Or you put the key file on a USB stick. The advantage of these types of tokens is that users cannot give them to others.

None of this is worth it if you have an active keylogger. Hardware keyloggers need extra consideration, but we want to ensure the boot path’s integrity for software keyloggers. This is where TPM can help. The TPM is hardware that provides no tampering with the hardware or critical parts of software, namely the BIOS.

Today, many FDE software and devices used in the corporate structure provide pre-boot authentication with multi-factor authentication and user identity to ensure maximum data protection while at the same time protecting against data theft with encryption.

Operating system providers have created many products by working on this subject. LUKS, which we see in Bitlocker in Windows, FileVault in macOS, and most Linux systems, help us encrypt the entire disk.

What Are the Requirements for PCI DSS Full Disk Encryption?

PCI DSS states that full disk encryption will help protect data in the event of physical loss of a disk. Therefore full disk encryption methods can be implemented for portable devices that store cardholder data.

There is a specific section for FDE in PCI DSS requirement 3.4.1 that states:

Suppose disk encryption is used instead of database encryption at the file or column level. In that case, logical access must be managed separately and independently of local operating system authentication and access control mechanisms. Decryption keys should not be associated with user accounts.

PCI says that besides having strong encryption and proper key management of encryption, there are a few other things to consider for full disk encryption:

  • Logical access must be separate and independent of native operating system authentication.
  • The decryption key should not be associated with the user account.

The keys used to decrypt the drive must be distinct from those used to log in to the operating system. The purpose behind this requirement is to create separation so that if the user’s authentication credentials are compromised, the decrypted data set will not automatically give anyone access to it.

When you have different authentication credentials, Microsoft BitLocker can be configured to do this. Still, the purpose of this particular requirement is to cause segregation, not allowing someone to automatically access the data set if the user’s authentication credentials are compromised.

See Also: Encryption Key Management Essentials

Using full-disk encryption makes it difficult to meet PCI Requirement 3.4 because when you boot the system and plug in the drive, it has transparent data encryption that the end-user can access. Disk-level encryption encrypts the entire disk or partition on a computer and automatically decrypts information when an authorized user requests it.

Many disk encryption solutions block operating systems, reads and writes, and perform the appropriate encryption conversions without any particular user action other than providing a password at system startup or the start of a session.

Based on these disk-level encryption features, it cannot use the same user account authenticator as the operating system to comply with this requirement. It cannot use public network login credentials associated with the system’s local user account database or a decryption key derived from it.

In short, all disk encryption should not rely solely on the operating system’s authentication process.

The best example of this is Microsoft BitLocker. BitLocker has several modes under which it can work. It can integrate with Active Directory (AD), rely on a trusted platform module (TPM) chip on the computer, or operate independently.

In standalone mode, BitLocker requires the user to manually enter the BitLocker key or provision the BitLocker key on a USB device that stores the BitLocker key to start the system. If this key is not provided, the system will not even offer the user to log in. This form of BitLocker satisfies the requests specified in PCI DSS 3.4.1 requirement.

In standalone mode, regarding the requirement that decryption keys should not be associated with user accounts, the BitLocker key also meets PCI DSS requirement 3.4.1 since the BitLocker key is not associated with the user’s credentials.

However, in AD or TPM modes, BitLocker runs in the background, and the end-user never knows that the disk is encrypted, and the user still logs into the system using their Windows credentials as usual.

AD or TPM modes do not meet the independence requirement in PCI DSS requirement 3.4.1 because the only thing that protects the data is the user’s Windows credentials. Also, in the case of AD mode, BitLocker does not meet the requirement to disassociate user credentials because the BitLocker decryption key is dependent on the user’s Windows credentials.

Summary

“Data at rest” means data stored anywhere. The location where this data is stored can be a mobile phone, laptop, server, or an external drive. While information is stored, it is not transferred from one place to another.

One of the ways to protect stored data in an encrypted form is through full disk encryption. Full disk encryption encrypts all of the information stored on the device, protecting it with a passphrase or other authentication method. On a mobile device or a laptop computer, this method usually has the device lock screen image. It would be best to have a passcode, passphrase, or fingerprint to decrypt full disk encryption. However, locking your device does not necessarily mean that full disk encryption is enabled on your device.

Examine how your operating system handles full disk encryption and how it is activated and managed. Full-disk encryption is allowed by default in some operating systems, but this may not be the case in others. The absence of disk encryption means anyone can access your data by entirely bypassing the lock on your device without the hassle of breaking the encryption on their device.

See Also: HSMs for PCI DSS Compliance

Some systems store various information in memory in an unencrypted form, even if you are using full disk encryption on your device. Memory (RAM) is a temporary drive, so it is usually impossible to read the information in memory when your device is powered down. However, it is technically possible for a sophisticated attacker to obtain information in memory with a cold boot attack.

Full disk encryption protects your data from people who have physical access to your device. Full disk encryption is a useful tool if you want to protect your data from housemates, coworkers or boss, family, partner, police, or other law enforcement. Full disk encryption protects your data even if you lose your device or theft.

There are other ways to encrypt stored data. “File encryption,” which encrypts individual files on your computer or another drive, is one such way. Another way is disk encryption, which encrypts a specific storage area on a device.

You can use the aforementioned stored data encryption methods together. Suppose you want to keep your medical documents. You can encrypt these documents individually using file encryption first. You can then use drive encryption to encrypt the partition where these files are located.

Finally, if you have enabled full disk encryption on your device, you can protect all other files on your drive along with your medical documents, including the operating system’s files.

Surkay Baykara
Surkay Baykarahttps://www.pcidssguide.com
A passionate Senior Information Security Consultant working at Cyberwise. Over the past 15+ years my professional career has included several positions beginning as a developer and IT administrator, working my way up to a senior Technical Performance Consultant before joining Biznet back in 2015. I had several different roles at Cyberwise, including Penetration Tester and PCI DSS QSA. In my job as a QSA, I found my passion and worked closely with the Audit and Compliance team. I've been working inside InfoSec for over 15 years, coming from a highly technical background. I have earned several certifications during my professional career including; CEH, CISA, CISSP, and PCI QSA.

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