  Traceability and integrity are major challenges for the increasingly complex
supply chains of today's world. Although blockchain technology has the
potential to address these challenges through providing a tamper-proof audit
trail of supply chain events and data associated with a product life-cycle, it
does not solve the trust problem associated with the data itself. Reputation
systems are an effective approach to solve this trust problem. However, current
reputation systems are not suited to the blockchain based supply chain
applications as they are based on limited observations, they lack granularity
and automation, and their overhead has not been explored. In this work, we
propose TrustChain, as a three-layered trust management framework which uses a
consortium blockchain to track interactions among supply chain participants and
to dynamically assign trust and reputation scores based on these interactions.
The novelty of TrustChain stems from: (a) the reputation model that evaluates
the quality of commodities, and the trustworthiness of entities based on
multiple observations of supply chain events, (b) its support for reputation
scores that separate between a supply chain participant and products, enabling
the assignment of product-specific reputations for the same participant, (c)
the use of smart contracts for transparent, efficient, secure, and automated
calculation of reputation scores, and (d) its minimal overhead in terms of
latency and throughput when compared to a simple blockchain based supply chain
model.
