As　the　next　generation　of　digital　microfluidic　biochips　(DMFBs)　platform,　Micro-electrode-dot-array　(MEDA)　has　sea-of-micro-electrodes　that　support　fine-grained　control　of　the　droplet　and　constant　real-time　monitoring　of　droplet　paths.　As　MEDA　biochips　are　expected　to　be　had　a　booming　market　in　the　near　future,　their　security,　especially　the　protection　of　intellectual　property　(IP),　has　become　the　focus　of　the　academic　community.　In　this　paper,　we　first　propose　a　logic　encryption-based　IP　protection　scheme　for　MEDA　biochips,　called　MEDASec,　which　is　without　modifying　the　structure.　Our　scheme　aims　to　hide　the　droplet　mix-split　operation　in　bioassay,　making　the　IP　akin　to　a　black-box　in　the　manufacturing　process.　Besides,　increasing　computing　power　has　facilitated　the　threat　of　brute　force　attacks　on　the　secret　key.　In　response　to　the　brute　force　attack,　we　propose　security　metrics　for　the　first　time,　called　RRA,　to　evaluate　the　ratio　of　reagents　that　result　from　biochemical　reactions.　Experimental　results　on　multiple　bioassays　demonstrate　the　effectiveness　of　the　proposed　logical　encryption　strategy　against　the　brute　force　attack.　©　2021　ACM.