Establishing Secure Communication Channels Using Remote Attestation with TPM 2.0.

Remote attestation allows a verifier to remotely check the integrity of a trusted computing platform. In recent years a number of attestation protocols based on Trusted Platform Modules (TPMs) have been proposed. These protocols cryptographically verify a trusted platform's state by exchanging TPM-signed quotes. Some of them also establish an encrypted channel to the trusted platform, which allows the verifier to transmit information that only the attested software stack can read. However, many existing attestation protocols are either vulnerable against man-in-the-middle attacks, or depend on outdated TPM specifications. In this work we analyze a recently developed attestation protocol that is being actively used to interconnect highly distributed trusted applications. We find this protocol to be vulnerable against a variant of the classical relay attack. In response to this threat we develop a lightweight remote attestation protocol based on the TPM 2.0 specification that is not vulnerable to this attack. Unlike previous proposals, our protocol relies solely on the TPM to establish a shared key on the attested channel, which significantly reduces its attack surface. Our protocol supports mutual attestation, perfect forward secrecy and is independent of the underlying network stack. We provide a reference implementation of our protocol and compare its performance to previous proposals. We also analyze its security properties using the Tamarin theorem prover.