  In IoT, smart sensors enable data collection, real-time monitoring,
decision-making, and automation, but their proliferation exposes them to
cybersecurity threats. Zero Trust Architecture enhances IoT security by
challenging conventional trust models and emphasizing continuous trust
verification in the overall \$875.0 billion IoT market projected by 2025. This
paper presents a new zero-trust real-time lightweight access control protocol
for Cloud-centric dynamic IoT sensor networks. This protocol empowers data
owners, referred to as sensor coordinators, to define intricate access
policies, blending recipient identifiers and data-related attributes for data
encryption. Additionally, the protocol incorporates efficient cryptographic
primitives, eliminating the need for reliance on a trusted party. Furthermore,
it ensures real-time data access while preserving data confidentiality and user
privacy through seamless data upload to the cloud and the offloading of
computationally intensive tasks from resource-constrained data owners and
sensors. The protocol utilizes Merkle Trees for lightweight, ongoing trust
measurement of sensors, ensuring efficient trust assessment by sensor
coordinators. Simultaneously, the cloud conducts thorough trust evaluations for
network entities including users. Comprehensive security analysis and
performance evaluation highlight the protocol's effectiveness in tackling the
multifaceted security challenges of IoT ecosystems while ensuring scalability
and high availability.
