  In this paper, we investigate joint power control and access point (AP)
selection scheme in a cell-free massive multiple-input multiple-output
(CF-mMIMO) system under an active eavesdropping attack, where an eavesdropper
tries to overhear the signal sent to one of the legitimate users by
contaminating the uplink channel estimation. We formulate a joint optimization
problem to minimize the eavesdropping spectral efficiency (SE) while
guaranteeing a given SE requirement at legitimate users. The challenging
formulated problem is converted into a more tractable form and an efficient
low-complexity accelerated projected gradient (APG)-based approach is proposed
to solve it. Our findings reveal that the proposed joint optimization approach
significantly outperforms the heuristic approaches in terms of secrecy SE
(SSE). For instance, the $50\%$ likely SSE performance of the proposed approach
is $265\%$ higher than that of equal power allocation and random AP selection
scheme.
