The　idea　of　multiuser　(nodes)　cooperation　is　an　efficient　way　to　improve　the　physical-layer　security　of　a　wireless　transmission　in　the　presence　of　passive　eavesdroppers.　However,　due　to　the　half-duplex　constraint　of　the　practical　transceivers,　two　phases　are　required　for　one　round　of　data　transmission,　which　grants　the　eavesdroppers　two　opportunities　to　wiretap　the　information.　Therefore,　protecting　the　data　transmissions　in　both　phases　is　critical.　Toward　this　end,　we　propose　a　joint　cooperative　beamforming,　jamming,　and　power-allocation　scheme　to　enhance　the　security　of　an　amplify-and-forward　(AF)　cooperative　relay　network　in　this　paper.　Different　from　the　existing　works　assuming　that　the　source　node　always　uses　its　total　power,　we　show　that　the　secrecy　rate　is　a　quasi-concave　function　of　the　power　of　the　source　node　so　that　allocating　its　total　power　may　not　be　optimal.　The　beamformer　design　and　power　optimization　problem　can　be　solved　by　a　bisection　method　together　with　a　generalized　eigenvalue　decomposition,　which　has　a　semiclosed　form　and　is　computationally　very　convenient.　Simulations　show　that　the　joint　scheme　greatly　improves　the　security.