  This paper considers a two-hop network architecture known as a combination
network, where a layer of relay nodes connects a server to a set of end users.
In particular, a new model is investigated where the intermediate relays employ
caches in addition to the end users. First, a new centralized coded caching
scheme is developed that utilizes maximum distance separable (MDS) coding,
jointly optimizes cache placement and delivery phase, and enables decomposing
the combination network into a set virtual multicast sub-networks. It is shown
that if the sum of the memory of an end user and its connected relay nodes is
sufficient to store the database, then the server can disengage in the delivery
phase and all the end users' requests can be satisfied by the caches in the
network. Lower bounds on the normalized delivery load using genie-aided cut-set
arguments are presented along with second hop optimality. Next recognizing the
information security concerns of coded caching, this new model is studied under
three different secrecy settings: 1) secure delivery where we require an
external entity must not gain any information about the database files by
observing the transmitted signals over the network links, 2) secure caching,
where we impose the constraint that end users must not be able to obtain any
information about files that they did not request, and 3) both secure delivery
and secure caching, simultaneously. We demonstrate how network topology affects
the system performance under these secrecy requirements. Finally, we provide
numerical results demonstrating the system performance in each of the settings
considered.
