AES-256 (Advanced Encryption Standard with a 256-bit key) is a symmetric encryption algorithm and one of the strongest widely available standards. It is recommended by BSI, NIST, and most national cybersecurity agencies.
In an ISMS context, AES-256 is the de facto standard for encrypting data at rest and frequently used within TLS for data in transit. ISO 27001 Annex A control A.8.24 (Use of Cryptography) requires a documented cryptography policy — this is where you define which algorithms and key lengths are permitted in your organization. AES-256 meets this requirement reliably. Pay attention to the cipher mode: GCM provides authenticated encryption, while CBC requires a separate integrity check.