With　the　development　of　the　Internet　of　Things　(IoT)　field,　more　and　more　data　are　generated　by　IoT　devices　and　transferred　over　the　network.　However,　a　large　amount　of　IoT　data　is　sensitive,　and　the　leakage　of　such　data　is　a　privacy　breach.　The　security　of　sensitive　IoT　data　is　a　big　issue,　as　the　data　is　shared　over　an　insecure　network　channel.　Current　solutions　include　symmetric　encryption　and　access　controls　to　secure　the　data　transfer,　but　they　have　some　drawbacks　such　as　a　single　point　of　failure.　Blockchain　is　a　promising　distributed　ledger　technology　that　can　prevent　the　malicious　tampering　of　data,　offering　reliable　data　storage.　This　paper　proposes　a　distributed　access　control　system　based　on　blockchain　technology　to　secure　IoT　data.　The　proposed　mechanism　is　based　on　fog　computing　and　the　concept　of　the　alliance　chain.　This　method　uses　mixed　linear　and　nonlinear　spatiotemporal　chaotic　systems　(MLNCML)　and　the　least　significant　bit　(LSB)　to　encrypt　the　IoT　data　on　an　edge　node　and　then　upload　the　encrypted　data　to　the　cloud.　The　proposed　mechanism　can　solve　the　problem　of　a　single　point　of　failure　of　access　control　by　providing　the　dynamic　and　fine-grained　access　control　for　IoT　data.　The　experimental　results　of　this　method　demonstrated　that　it　can　protect　the　privacy　of　IoT　data　efficiently.