Relational database encryption protects sensitive data by converting it into unreadable ciphertext using cryptographic algorithms. This process ensures that even if unauthorized users access the database files or backups, they cannot interpret the data without the correct decryption keys. Encryption can be applied at different levels: entire databases, specific tables, columns, or individual fields. The choice depends on security requirements and performance trade-offs. For example, encrypting a “credit_card” column ensures card numbers are secure, while leaving non-sensitive data like product descriptions unencrypted maintains query efficiency.
There are two primary encryption methods: application-level and database-level. In application-level encryption, data is encrypted before being sent to the database, giving developers full control over algorithms and keys. For instance, a payment service might use AES-256 in their code to encrypt customer Social Security numbers before storing them. Database-level encryption, such as Transparent Data Encryption (TDE), is handled by the database engine itself. TDE automatically encrypts data at rest (e.g., on disk) without requiring changes to applications. While convenient, TDE doesn’t protect against attacks where an attacker gains direct database access through valid credentials, as the database decrypts data for authorized users automatically. Some systems also support column-specific encryption, allowing granular control—like encrypting a “password” column with a function like ENCRYPTBYKEY() in SQL Server.
Key management is critical. Encryption keys must be stored separately from the data they protect, often using a dedicated key management service (KMS) or hardware security modules (HSMs). For example, AWS RDS integrates with AWS KMS to manage keys for TDE. Access controls (e.g., database roles) determine who can decrypt data, ensuring only authorized applications or users have key access. A common pitfall is neglecting key rotation or backup strategies, which can lead to data loss if keys are compromised. While encryption adds overhead—such as slower queries for encrypted columns—it’s a foundational layer that works alongside other security measures like network encryption (TLS for data in transit) and role-based access controls.