ll,uli. rt:al-t.iliif,{lat,al]aseapplications miseinsdety-criticd installations andmilitary systems where enforcing security t> irtt~Ml to th(, successor the enterprise. A secure real-time (liiti]l)~<(, svstrm has to simultaneously satisfy two require-II1(J1l Is guarauree data security and minimize the number ,,1 Ititw,d transaction deadlines. We investigate here the p,ukmuance implications, in terms of missed deadlines, of gu;uallt.veiug secorit.y in a real-time database system. In lwtitulal. w{' focus on the concurrency control aspects of 1111> 15>11(, (hlr lll;l]tl ({)jlt.ril)~it,iollsu et hefollowing: First, we iden-Lt]"vwhich a.umug the previously proposed real-time concur-IIIK.K((lrlt.rol protocols" are capable of providing protection ,i~;iil~si })[}th (Im:(t aud imlirect (covert channels) means of lllla!ltt]~mzrd Mress to data. Second. using a detailed simolimou model of a firm-deadline real-time database system, wv profile the real-time performance of a representative set ,)1 illtw, s~~(ur[ (om.orrmi(:y control protocols. Our exper-IILIIIIIIs show that. a prioritized optimistic concurrency control protocol. OPT-WAIT, provides the best overall perforii,ium Third. we propose and evaluate a novel durd ap-lmMrlI to secure t,rimsaction concurrency control that al-1,,~~> tll(' rml-time (latabase system to simultaneously use tlIffIw,III c(ulrvlrreucy control mechanisms for guaranteeing (,{II IIIV ,UI{I fijr imprcn,iug real-time performance. By appropriately ckoosing these different mechanisms, we have IML(OII al)h, to (Iesign hyfwui concurrency control algorithms 111,11 lJII)\.1~1{1 (,v(,II Iwttw performance than OPT-WAIT.