  The vast areas of applications for IoTs in future smart cities, smart
transportation systems, and so on represent a thriving surface for several
security attacks with economic, environmental and societal impacts. This survey
paper presents a review of the security challenges of emerging IoT networks and
discusses some of the attacks and their countermeasures based on different
domains in IoT networks. Most conventional solutions for IoT networks are
adopted from communication networks while noting the particular characteristics
of IoT networks such as the nodes quantity, heterogeneity, and the limited
resources of the nodes, these conventional security methods are not adequate.
One challenge toward utilizing common secret key-based cryptographic methods in
large-scale IoTs is the problem of secret key generation, distribution, and
storage and protecting these secret keys from physical attacks. Physically
unclonable functions (PUFs) can be utilized as a possible hardware remedy for
identification and authentication in IoTs. Since PUFs extract the unique
hardware characteristics, they potentially offer an affordable and practical
solution for secret key generation. However, several barriers limit the PUFs'
applications for key generation purposes. We discuss the advantages of
PUF-based key generation methods, and we present a survey of state-of-the-art
techniques in this domain. We also present a proof-of-concept PUF-based
solution for secret key generation using resistive random-access memories
(ReRAM) embedded in IoTs.
