Encryption at Rest

Encryption at rest protects data while it is stored, as opposed to while it moves across a network. It ensures that if storage media, backups, or database files are stolen or improperly accessed, the contents remain unreadable without the encryption keys.

How It Works

Data at rest is encrypted using strong symmetric algorithms, most commonly AES-256. Encryption can happen at several layers: full-disk encryption protects entire volumes, file-level encryption protects individual files, and database or column-level encryption protects specific fields such as payment data.

Key management is the critical part. Data encryption keys (DEKs) encrypt the actual data, and key encryption keys (KEKs) protect the DEKs. A dedicated key management service (KMS) or hardware security module (HSM) stores and rotates keys safely. Cloud providers offer managed KMS services, and many storage systems enable encryption at rest by default.

Envelope encryption is a common pattern: the KMS encrypts a per-object DEK, which is stored alongside the ciphertext, reducing exposure of the master key.

Why It Matters

Physical theft, decommissioned drives, and misconfigured storage buckets are real threats. Encryption at rest renders such exposed data useless to an attacker who lacks the keys.

Many regulations and standards, including GDPR, HIPAA, and PCI DSS, expect or require encryption of sensitive stored data. It is also a standard layer in defense in depth.

Encryption at rest alone is not enough; it protects against storage compromise but not against an attacker who already has valid application access. It must be paired with encryption in transit, access controls, and sound key management.

Related Terms

Encryption at rest complements encryption in transit and relies on symmetric encryption and disciplined secrets management. Public key infrastructure often protects the keys.