  Blockchain creates a secure environment on top of strict cryptographic
assumptions and rigorous security proofs. It permits on-chain interactions to
achieve trustworthy properties such as traceability, transparency, and
accountability. However, current blockchain trustworthiness is only confined to
on-chain, creating a "trust gap" to the physical, off-chain environment. This
is due to the lack of a scheme that can truthfully reflect the physical world
in a real-time and consistent manner. Such an absence hinders further
real-world blockchain applications, especially for security-sensitive ones.
  In this paper, we propose a scheme to extend blockchain trust from on-chain
to off-chain, and take trustworthy vaccine transportation as an example. Our
scheme consists of 1) a Trusted Execution Environment (TEE)-enabled trusted
environment monitoring system built with the Arm Cortex-M33 microcontroller
that continuously senses the inside of a vaccine box through trusted sensors
and generates anti-forgery data; and 2) a consistency protocol to upload the
environment status data from the TEE system to blockchain in a truthful,
real-time consistent, continuous and fault-tolerant fashion. Our security
analysis indicates that no adversary can tamper with the vaccine in any way
without being captured. We carry out an experiment to record the internal
status of a vaccine shipping box during transportation, and the results
indicate that the proposed system incurs an average latency of 84 ms in local
sensing and processing followed by an average latency of 130 ms to have the
sensed data transmitted to and available in the blockchain.
