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This paper considers a two-hop network architecture known as a combinationnetwork, 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 employcaches in addition to the end users. First, a new centralized coded cachingscheme is developed that utilizes maximum distance separable (MDS) coding,jointly optimizes cache placement and delivery phase, and enables decomposingthe combination network into a set virtual multicast sub-networks. It is shownthat if the sum of the memory of an end user and its connected relay nodes issufficient to store the database, then the server can disengage in the deliveryphase and all the end users' requests can be satisfied by the caches in thenetwork. Lower bounds on the normalized delivery load using genie-aided cut-setarguments are presented along with second hop optimality. Next recognizing theinformation security concerns of coded caching, this new model is studied underthree different secrecy settings: 1) secure delivery where we require anexternal entity must not gain any information about the database files byobserving the transmitted signals over the network links, 2) secure caching,where we impose the constraint that end users must not be able to obtain anyinformation about files that they did not request, and 3) both secure deliveryand secure caching, simultaneously. We demonstrate how network topology affectsthe system performance under these secrecy requirements. Finally, we providenumerical results demonstrating the system performance in each of the settingsconsidered.

Combination Networks with or without Secrecy Constraints: The Impact of Caching Relays