  Many applications, e.g., digital twins, rely on sensing data from Internet of
Things (IoT) networks, which is used to infer event(s) and initiate actions to
affect an environment. This gives rise to concerns relating to data integrity
and provenance. One possible solution to address these concerns is to employ
blockchain. However, blockchain has high resource requirements, thereby making
it unsuitable for use on resource-constrained IoT devices. To this end, this
paper proposes a novel approach, called two-layer directed acyclic graph
(2LDAG), whereby IoT devices only store a digital fingerprint of data generated
by their neighbors. Further, it proposes a novel proof-of-path (PoP) protocol
that allows an operator or digital twin to verify data in an on-demand manner.
The simulation results show 2LDAG has storage and communication cost that is
respectively two and three orders of magnitude lower than traditional
blockchain and also blockchains that use a DAG structure. Moreover, 2LDAG
achieves consensus even when 49\% of nodes are malicious.
