  This paper studies device to device (D2D) coded-caching with information
theoretic security guarantees. A broadcast network consisting of a server,
which has a library of files, and end users equipped with cache memories, is
considered. Information theoretic security guarantees for confidentiality are
imposed upon the files. The server populates the end user caches, after which
D2D communications enable the delivery of the requested files. Accordingly, we
require that a user must not have access to files it did not request, i.e.,
secure caching. First, a centralized coded caching scheme is provided by
jointly optimizing the cache placement and delivery policies. Next, a
decentralized coded caching scheme is developed that does not require the
knowledge of the number of active users during the caching phase. Both schemes
utilize non-perfect secret sharing and one-time pad keying, to guarantee secure
caching. Furthermore, the proposed schemes provide secure delivery as a side
benefit, i.e., any external entity which overhears the transmitted signals
during the delivery phase cannot obtain any information about the database
files. The proposed schemes provide the achievable upper bound on the minimum
delivery sum rate. Lower bounds on the required transmission sum rate are also
derived using cut-set arguments indicating the multiplicative gap between the
lower and upper bounds. Numerical results indicate that the gap vanishes with
increasing memory size. Overall, the work demonstrates the effectiveness of D2D
communications in cache-aided systems even when confidentiality constraints are
imposed at the participating nodes and against external eavesdroppers.
