Device attestation
Design a device-attestation system that lets a backend verify that a connecting client is running on genuine, unmodified hardware/software before granting access to sensitive APIs — covering 30M mobile and IoT devices. Threat model: rooted/jailbroken devices, emulators, replayed attestation tokens, and cloned device identities. Hardware capabilities vary: some devices have a TPM/secure enclave, many cheap IoT devices have none. The verification must add under 200ms to a session handshake and survive a key-extraction attempt on any single device without compromising the fleet. Cover the attestation protocol, the trust root, replay protection, and how you handle devices with no secure hardware.
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.