Secure　data　ownership　management　is　significant　for　realizing　personal　and　private　data　sharing,　which　can　be　widely　used　with　consumer　electronics.　The　notion　of　the　decentralized　privacy　(DP)　is　introduced　by　Zyskind　et　al.,　and　accordingly　the　first　DP　system　is　implemented　through　blockchain　and　off-blockchain　distributed　hashtable.　To　address　the　efficiency　and　overhead　issues,　we　present　a　conceptually　simple　solution　directly　from　smart　contracts　with　cryptographic　primitives.　Our　system　is　called　the　smart　contract-based　decentralized　privacy　(SCDP)　system.　We　propose　the　basic　SCDP　system　as　a　warm-up　to　introduce　the　design　principle　based　on　symmetric　encryption.　Moreover,　the　strong　SCDP　system　is　provided　by　using　ciphertext-policy　attribute-based　encryption　for　supporting　more　flexible　scenarios　of　access　control　and　also　eliminating　some　limitations　of　the　basic　system.　©　2019　IEEE.