Remote Attestation (RA) is a security mechanism that allows a centralized trusted entity (Verifier) to check the trustworthiness of a potentially compromised IoT device (Prover). With the tsunami of interconnected IoT devices, the advancement of swarm RA schemes that efficiently attest large IoT networks has become crucial. Recent swarm RA approaches work towards distributing the attestation verification from a centralized Verifier to many Verifiers. However, the assumption of trusted Verifiers in the swarm is not practical in large networks. In addition, the state-of-the-art RA schemes do not establish network-wide decentralized trust among the interacting devices in the swarm. This paper proposes PERMANENT, a Publicly Verifiable Remote Attestation protocol for Internet of Things through Blockchain, which stores the historical attestation results of all devices in a blockchain and allows each interacting device to obtain the attestation result. PERMANENT enables devices to make a trust decision based on the historical attestation results. This feature allows the interaction among trustworthy devices (or with a trust score over a certain threshold) without the computational overhead of attesting every participating device before each interaction. We validate PERMANENT with a proof-of-concept implementation, using Hyperledger Sawtooth as the underlying blockchain. The conducted experiments confirm the feasibility of the PERMANENT protocol
