AES-256 (Advanced Encryption Standard with 256-bit key length) is the gold standard for symmetric encryption, approved by NIST in 2001. Used by the US government for top-secret data, it provides 2^256 possible key combinations — computationally infeasible to brute-force. AES-256-GCM is the most common authenticated implementation used across password managers, cloud storage, and secure messaging apps.
| Standard | NIST FIPS 197 |
| Key Length | 256-bit |
| Block Size | 128-bit |
| Mode | GCM (Galois/Counter Mode) — most common |
| Security | Computationally infeasible to brute-force |
| Approved By | NSA, NIST, ISO/IEC 18033-3 |
| Performance Impact | Negligible on modern hardware with AES-NI |