  This letter considers the secure communication in a reconfigurable
intelligent surface (RIS) aided full duplex (FD) system. An FD base station
(BS) serves an uplink (UL) user and a downlink (DL) user simultaneously over
the same time-frequency dimension assisted by a RIS in the presence of an
eavesdropper. In addition, the artificial noise (AN) is also applied to
interfere the eavesdropper's channel. We aim to maximize the sum secrecy rate
of UL and DL users by jointly optimizing the transmit beamforming, receive
beamforming and AN covariance matrix at the BS, and passive beamforming at the
RIS. To handle the non-convex problem, we decompose it into tractable
subproblems and propose an efficient algorithm based on alternating
optimization framework. Specifically, the receive beamforming is derived as a
closed-form solution while other variables are obtained by using semidefinite
relaxation (SDR) method and successive convex approximation (SCA) algorithm.
Simulation results demonstrate the superior performance of our proposed scheme
compared to other baseline schemes.
