On the Covertness of Multi-User Wireless Networks Under Injection Attacks

This letter addresses covert communication in multi-user wireless networks under cognitive adversarial reactive injection attacks. To protect the user links, a secret-key strategy is employed in which each user embeds its ON-OFF keying (OOK) symbols in an orthogonal mask and a frame-wise energy schedule drawn from a public dictionary. After key-aided demasking and energy normalization, the receiver Bob's decision reduces to a variance test. We derive closed-form likelihood-ratio thresholds and error probabilities for Rayleigh slow and fast fading channel conditions, modeling the adversary Eve's full-duplex injection as interference that changes the variance between ON state and OFF state transmissions. Asymptotically, error probabilities decay polynomially in the number of channel uses N under slow fading but exponentially under fast fading. Simulations validate these closed-form expressions, revealing clear gains in slow fading and fast fading conditions as N increases. The results show that key-assisted energy randomization and channel time variation jointly strengthen covertness against active injection attacks.