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In this paper, we study the physical layer security problem in the dual‐hop orthogonal frequency division multiplexing–based wireless communication system. First, we consider a single‐user single‐relay system and study a joint power optimization problem at the source and relay subject to individual power constraint at the 2 nodes. The aim is to maximize the end‐to‐end secrecy rate with optimal power allocation over different subcarriers. Later, we consider a more general multiuser multirelay scenario. Under high signal‐to‐noise ratio approximation for end‐to‐end secrecy rate, an optimization problem is formulated to jointly optimize power allocation at the base station, the relay selection, subcarrier assignment to users, and the power loading at each of the relaying node. The target is to maximize the overall security of the system subject to independent power budget limits at each transmitting node and the …