Symmetric encryption uses a single key shared between parties. It processes data faster but requires secure key distribution before communication begins. Asymmetric methods use paired keys—public for encryption, private for decryption. This eliminates the distribution problem but runs slower on identical hardware.

AES-256 remains the industry standard for file encryption in 2024. It balances proven security with practical performance on modern processors. Avoid deprecated methods like DES or RC4 regardless of compatibility concerns—those vulnerabilities are well-documented and actively exploited.

Technically possible but defeats the purpose. If an attacker gains database access, they retrieve both keys and data in one breach. Store keys in separate infrastructure—hardware security modules for sensitive systems, environment variables with restricted access for typical applications, or dedicated key management services.

Rotation frequency depends on data sensitivity and regulatory requirements. Financial services typically rotate quarterly. Healthcare systems follow annual schedules unless compromise is suspected. Design your architecture to support rotation without service interruption—versioned keys let you decrypt old data while encrypting new content with updated credentials.

Data becomes permanently inaccessible. Strong encryption offers no backdoor recovery method by design. Implement secure backup procedures—split keys across multiple secure locations, use threshold schemes requiring partial keys from different administrators, or maintain encrypted key escrow systems with strict access controls.

Transport encryption protects data moving between systems but leaves it exposed at rest. Comprehensive protection requires encryption at every stage—in transit over networks, at rest in databases and backups, and in memory during processing when feasible. Each layer addresses different attack vectors.