A Key to Embedded System Security: Locking and Unlocking Secrets with a Trusted Platform Module.

Security hardware modules were designed to provide a viable solution that can empower Embedded Systems (ES) with state-of-the-art cryptographic and security capabilities. They can execute cryptographic operations, securely store sensitive information, or provide measurements for attestation. A key element in designing and implementing security solutions on top of a security hardware, such as the Trusted Platform Module (TPM), is secure secret storage. The work at hand addresses the problem of secret protection by showcasing how the TPM standard can serve as a vault in protecting sensitive information in ES. This is accomplished as follows. Secrets are locked in the TPM according to Platform Configuration Register (PCR) policies created on top of the system state and sealing. In contrast, unlocking is achieved through TPM unsealing. In both cases, secure and authenticated sessions are enforced while communicating with the TPM. Furthermore, our work goes a step further and presents a simple TPM attestation protocol, destined to verify the system state and TPM application. Lastly, a series of experiments were conducted on a reference hardware, with two different TPM configurations, to measure execution times of TPM operations.