In　this　paper,　an　efficient　video　encryption　scheme　is　proposed　for　protecting　H.264　bitstream.　The　issues　on　the　compressed　domain　video　encryption　have　been　pointed　out　and　fully　addressed.　In　the　proposed　scheme,　only　the　most　significant　bits　for　video　reconstruction　in　H.264　bitstream　are　extracted　and　encrypted,　to　optimize　the　trade-off　between　security　level　and　computational　complexity.　For　intra-frames,　only　the　codewords　of　intra　4×4　prediction　mode　and　the　sign　bits　of　the　low　frequency　DCT　coefficient　are　encrypted.　For　inter-frames,　the　info-suffix　of　motion　vector　difference　(MVD)　are　encrypted.　Owing　to　the　proposed　scheme　is　independent　of　the　compression　process,　thus　does　not　need　to　modify　the　structure　of　H.264　standard　codec.　Experimental　results　show　that　the　proposed　scheme　exhibits　significant　computational　efficiency　and　reliable　security,　can　resist　not　only　perceptual　attacks　but　also　brute-force　attacks.　Furthermore,　it　adds　a　little　memory　overhead.　Therefore,　the　proposed　scheme　will　be　well　suited　for　real-time　video　applications　and　resource-limited　systems　such　as　smartphone　and　wireless　sensor　network.　©　2013　GIRI.