  Fog computing is a paradigm for distributed computing that enables sharing of
resources such as computing, storage and network services. Unlike cloud
computing, fog computing platforms primarily support {\em non-functional
properties} such as location awareness, mobility and reduced latency. This
emerging paradigm has many potential applications in domains such as smart
grids, smart cities, and transport management.
  Most of these domains collect and monitor personal information through edge
devices to offer personalized services. A {\em centralized} server either at
the level of cloud or fog, has been found ineffective to provide a high degree
of security and privacy-preserving services.
  Blockchain technology supports the development of {\em decentralized}
applications designed around the principles of immutability, cryptography,
consistency preserving consensus protocols and smart contracts. Hence
blockchain technology has emerged as a preferred technology in recent times to
build trustworthy distributed applications.
  The chapter describes the potential of blockchain technology to realize
security services such as authentication, secured communication, availability,
privacy and trust management to support the development of dependable fog
services.
