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What is meant by encryption at rest?

Encryption at rest refers to the encryption of data that is stored physically in any digital form. This data can include files, databases, backups, archives, and more. The main goal of encryption at rest is to protect data that is not actively moving between systems or networks from unauthorized access or use while at rest. Some key things to know about encryption at rest:

Why is encryption at rest important?

Encryption at rest is a critical security measure for a few key reasons:

  • Protects sensitive data – Encryption at rest helps protect confidential or sensitive data like financial records, healthcare data, personal information, intellectual property, etc. from attackers even if they gain physical access to the storage media.
  • Compliance with regulations – Many regulations like HIPAA, PCI DSS, and GDPR require encryption of sensitive data at rest as part of compliance obligations.
  • Mitigates data breaches – Encryption at rest makes stolen or lost data unreadable and unusable for attackers, limiting the impact of data breaches.
  • Defense-in-depth – Encryption at rest provides an added layer of security on top of access controls and other measures as part of a defense-in-depth strategy.

When is data at rest encrypted?

Here are some of the most common examples of data at rest that organizations encrypt:

  • Files/folders – Encrypting files and folders protects data stored on laptops, desktops, servers, external media, network shares, cloud storage, archives, backups, etc.
  • Databases – Database encryption protects structured data like financial transactions, customer information, intellectual property, etc. Common methods include TDE and field-level encryption.
  • Backups – Encrypting backups protects data in long-term archives and stored backup media against unauthorized restoration.
  • Mobile devices – Encrypting data on smartphones, tablets, and other mobile devices protects against device theft or loss.
  • Cloud services – Encryption applied to data stored with cloud service providers like SaaS applications, IaaS storage, PaaS databases, etc.

Where does encryption at rest take place?

Encryption at rest can take place at different levels within an IT infrastructure:

  • Application-level – Encryption built into software applications like document editors, email clients, ERP systems, etc. to encrypt specific files.
  • Database-level – Encryption applied to an entire database (TDE) or specific columns/fields via database encryption features.
  • Filesystem-level – Encryption enforced at the filesystem level to encrypt all files written to specific volumes, drives, directories, etc.
  • Disk/drive-level – Full disk encryption solutions that encrypt at the hardware level on servers, laptops, external drives, etc.
  • Cloud service-level – Encryption applied to data by cloud providers such as SaaS apps, IaaS storage, PaaS databases, etc.

How does encryption at rest work?

Encryption at rest works by using an encryption algorithm and encryption key to transform plaintext data into cipher text when writing it to physical storage. The decryption key is then required to decrypt this cipher text back into usable plaintext when reading it. Here is a simple overview of the process:

  1. Plaintext data is passed to the encryption algorithm as input.
  2. The algorithm uses a randomly generated encryption key to transform the plaintext into encrypted cipher text.
  3. The cipher text is stored in place of the plaintext on disk, backup media, etc.
  4. To access the plaintext again, the decryption key is used by the algorithm to decrypt the cipher text.
  5. The original plaintext data is returned and readable again.

This protects confidentiality of data at rest because attackers who gain access to the storage media will only see unreadable cipher text without the encryption keys.

What encryption algorithms are used?

Some common encryption algorithms used for encryption at rest include:

  • AES (Advanced Encryption Standard) – Symmetric encryption standard used widely for files, databases, etc. Common key lengths are 128, 192 and 256 bit.
  • RSA – Asymmetric/public key algorithm often used for encryption key storage, key exchange, signatures, etc.
  • Blowfish, Twofish, Serpent – Symmetric algorithms used less commonly than AES.
  • 3DES – Legacy symmetric algorithm that is being replaced by AES.
  • Elliptic curve cryptography – Used for asymmetric encryption and digital signatures. May offer performance benefits over RSA.

Additionally, algorithms are often combined in modes of operation like CBC, XTS, GCM to provide additional cryptographic operations.

What are the methods of encryption at rest?

There are a few common methods used to implement encryption at rest in various products and solutions:

  • Transparent encryption – Encryption is handled transparently without user interaction e.g. at filesystem, disk, cloud service levels.
  • File/folder encryption – Users selectively encrypt specific files and folders via application features.
  • Full disk encryption – Entire volumes or disks are encrypted at the block level transparently.
  • Field-level encryption – Specific fields or columns in a database are encrypted transparently.
  • Application encryption – Applications encrypt specific files, data objects, backups, communications, etc.

The methods used depend on the specific data to be protected and system architectures involved. A hybrid approach using multiple methods is common.

What are best practices for encryption at rest?

Some best practices to follow for implementing encryption at rest include:

  • Encrypt data rather than focusing just on encrypting devices or media that store it.
  • Align encryption with classification policies based on data sensitivity and risk.
  • Use strong, industry-tested encryption algorithms and sufficient key lengths.
  • Properly generate, protect and rotate encryption keys.
  • Enforce encryption broadly across multiple layers like app, database, filesystem, network.
  • Manage encryption centrally where possible through Enterprise Key Management (EKM).
  • Document detailed encryption configurations, policies and procedures.
  • Monitor for unauthorized decryption, key changes, and other tampering.

Following these best practices allows organizations to apply encryption at rest in a secure, controlled, auditable manner.

What are the challenges with implementing encryption at rest?

Some potential challenges with adoption of encryption at rest include:

  • Performance impacts – Encryption/decryption operations can reduce performance of applications and storage systems.
  • Key management – Securely generating, distributing, rotating and storing keys adds overhead.
  • Cost – Encryption software, hardware, Cloud KMS services, etc. add licensing, deployment and management costs.
  • Complexity – Designing, implementing and maintaining encryption across diverse environments with varied data can be complex.
  • Legacy compatibility – Older systems may not work with newer encryption protocols and algorithms.
  • Lack of native support – Some applications and platforms still lack built-in encryption capabilities.

These challenges can be mitigated through careful assessment, testing, project planning and working with encryption vendors and service providers where needed.


Encryption at rest is a vital security control for protecting data confidentiality and supporting compliance obligations. Organizations should evaluate their data security risks and requirements to determine where implementing strong encryption at rest provides the most value. With proper key management and careful rollout, encryption at rest can be deployed both widely and efficiently to become a fundamental component of a defense-in-depth data security strategy.