Ciphertext　retrieval　under　heterogeneous　data　sets　is　a　critical　concern　in　the　cloud-assisted　Internet　of　Things　(IoT).　Previous　ciphertext　retrieval　schemes　eliminate　computation　burden　and　security　concerns　to　some　extent,　but　cannot　support　the　encrypted　heterogeneous　data　sets.　To　solve　this　problem,　in　this　article　we　propose　a　transparent　ciphertext　retrieval　system　regardless　of　programming　language,　accessible　platforms,　and　heterogeneity　of　data　sets.　The　retrieval　system　is　a　novel　combination　of　the　proposed　access　and　integration　middleware　with　a　current　encrypted　cloud　database　system.　The　middleware　enables　cross-language　and　cross-platform　queries　over　various　database　systems,　besides,　it　schedules　the　designed　data　integration　method　in　heterogeneous　databases　to　realize　cross-database　queries　over　the　encrypted　cloud　data　sets.　The　proposed　ciphertext　retrieval　system　achieves　efficient　data　sharing　among　different　IoT　applications　with　various　database　systems.　We　prove　that　the　system　guarantees　data　security　by　avoiding　malicious　hackers.　Extensive　experiments　show　that　our　design　is　efficient　and　feasible　in　practice.