  The recently accentuated features of augmenting conventional wireless
networks with high altitude platform systems (HAPS) have fueled a plethora of
applications, which promise to offer new services to ground users, as well to
enhance the efficiency and pervasion of existing applications. Cloud-enabled
HAPS, which aims to create HAPS-based datacenters that offer cloud services to
users, has particularly emerged as a promising key enabler to provide
large-scale equitable services from the sky. Although offering cloud services
from the HAPS proves to be efficient, its practical deployment at the
stratosphere level still faces many challenges such as high energy
requirements, physical maintenance, and is particularly prone to security
considerations. Safeguarding the cloud-enabled HAPS against various
cyberattacks is a necessity to guarantee its safe operation. This paper
proposes a blockchain model to secure cloud-enabled HAPS networks that contain
a large number of HAPS stations from recurring cyberattacks within the context
of the environment and infrastructure monitoring (EIM) application. To this
end, the paper first presents a detailed blockchain framework, and describes
the ways of integrating the developed framework into the various system
components. We then discuss the details of the system implementation, including
the storing and consuming of cloud transactions, the generation of new blocks,
and the blockchain consensus protocol that is tailored to the EIM requirements.
Finally, we present numerical simulations that illustrate the performance of
the system in terms of throughput, latency, and resilience to attacks.
