Encryption at Rest

Encryption at rest encrypts data while it is stored, so leaked media remain unreadable; it requires accompanying key management.

Purpose

To protect the confidentiality of data on storage media (disks, backups, SSDs) against physical theft.

Mechanism

Data is encrypted before being written to storage and decrypted on read, transparent to the application (implemented by the storage layer or OS). Key management is critical: a KMS (key management service) holds the master key, and data keys encrypt the data. Common examples: LUKS (Linux full disk), FileVault (macOS), TDE (databases).

Use cases

Database TDE
Cloud storage encryption (S3 SSE)
Full-disk encryption (LUKS/BitLocker)
Backup encryption

Examples

Input
```
Disk data + KMS key
```
Output
```
Encrypted storage
```
Keys separated from data

Common errors

Storing keys alongside the data: Keep keys in KMS/HSM, separated from encrypted data

Related terms

The Advanced Encryption Standard (AES) is the symmetric block cipher NIST standardized in 2001, supporting 128/192/256-bit keys, and is the de facto standard of modern encryption.

Key derivation is the process of generating encryption keys from low-entropy passwords or high-entropy master keys, using KDFs (e.g., PBKDF2, scrypt, Argon2) to raise the cost of brute force.

X.509 Certificate

An X.509 certificate binds a public key to an identity, signed by a CA for verification, containing validity, issuer, subject, and extension fields.

References