Encryption and key management

Design an encryption-at-rest and key-management system for a platform storing billions of customer records, where each customer wants their own encryption key (so you can cryptographically delete a customer by destroying their key), keys must rotate without re-encrypting petabytes of data, and a compromised key must be revocable. Throughput: 200K encrypt/decrypt ops/sec. Walk through the key hierarchy, how rotation works without rewriting all data, and how per-customer 'crypto-shredding' deletion works.