  Flexible resources in built environments are seen as a low-cost opportunity
for delivering grid management services. Consequently, the centralised
aggregator model, where the aggregator is used to bundle demand flexibility
from flexible resources and deliver it to flexibility customers such as
Distributed/Transmission System Operator (DSO/TSO) in flexibility markets, has
been adopted. However, the aggregator role introduces various security and
trust challenges. In this work, we propose a blockchain-based flexibility
trading framework dubbed PlexiChain to address the security and trust
challenges the aggregator poses in the centralised aggregator model. The
security evaluations performed using a real-world dataset show that PlexiChain
is robust against known security attacks, such as MadIoT and False Data
Injection attacks. Additionally, the performance evaluations show that
PlexiChain has lower computation and communication costs than other
blockchain-based applications in resource-constrained environments.
