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We consider a secure overlay cognitive radio network with an eavesdropper wherein a multi-antenna secondary transmitter performs transmission in primary spectrum, on the condition that it helps primary system to perform secure and reliable transmission via cooperative relaying and jamming. To improve secrecy performance of primary network, we propose full-duplex jammer protocol and zero-forcing based beamforming design, which completely cancels the interferences at the primary and secondary users and simultaneously avoids the leakage of confidential information to eavesdropper. Moreover, we present new expressions for the average secrecy rate and a lower bound for the secrecy outage probability. Furthermore, an asymptotic analysis in the high signal-to-noise ratio regime is carried out to obtain closed-form average secrecy rate. Our analytical findings reveal that by exploiting beamforming and full …