  This work investigates a system where each user aims to retrieve a scalar
linear function of the files of a library, which are Maximum Distance Separable
coded and stored at multiple distributed servers. The system needs to guarantee
robust decoding in the sense that each user must decode its demanded function
with signals received from any subset of servers whose cardinality exceeds a
threshold. In addition, (a) the content of the library must be kept secure from
a wiretapper who obtains all the signals from the servers;(b) any subset of
users together can not obtain any information about the demands of the
remaining users; and (c) the users' demands must be kept private against all
the servers even if they collude. Achievable schemes are derived by modifying
existing Placement Delivery Array (PDA) constructions, originally proposed for
single-server single-file retrieval coded caching systems without any privacy
or security or robustness constraints. It is shown that the PDAs describing the
original Maddah-Ali and Niesen's coded caching scheme result in a load-memory
tradeoff that is optimal to within a constant multiplicative gap, except for
the small memory regime when the number of file is smaller than the number of
users. As by-products, improved order optimality results are derived for three
less restrictive systems in all parameter regimes.
