Various aspects of the present disclosure generally relate to wireless communication. In some aspects, a user equipment (UE) may receive a first signal associated with a downlink control channel, wherein the first signal uses a modulation signature that identifies a first security key associated with a reconfigurable intelligent surface (RIS), and wherein the first signal includes a second security key. The UE may receive a second signal associated with a downlink shared channel, wherein the second signal includes a third security key, and wherein the second signal is authenticated by the UE based at least in part on the first security key, the second security key, and the third security key. Numerous other aspects are described.