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.