Secure vault — encryption, keys, and auditing

Production vaults use approved algorithms (e.g., AES-256-GCM), hardware security modules, and key rotation—classroom XOR demos are not substitutes.

Audit trails should be append-only with tamper evidence; here they are PHP arrays for illustration only.

Recovery keys and split knowledge (M-of-N) protect against single-admin compromise.

Link two-factor authentication when explaining who may decrypt after authentication.