  Prior to provisioning sensor data to smart contracts, a pre-processing of the
data on intermediate off-chain nodes is often necessary. When doing so,
originally constructed cryptographic signatures cannot be verified on-chain
anymore. This exposes an opportunity for undetected manipulation and presents a
problem for applications in the Internet of Things where trustworthy sensor
data is required on-chain. In this paper, we propose trustworthy pre-processing
as enabler for end-to-end sensor data integrity in data on-chaining workflows.
We define requirements for trustworthy pre-processing, present a model and
common workflow for data on-chaining, select off-chain computation utilizing
Zero-knowledge Proofs (ZKPs) and Trusted Execution Environments (TEEs) as
promising solution approaches, and discuss both our proof-of-concept
implementations and initial experimental, comparative evaluation results. The
importance of trustworthy pre-processing and principle solution approaches are
presented, addressing the major problem of end-to-end sensor data integrity in
blockchain-based IoT applications.
