Various aspects of the present disclosure generally relate to wireless communication. In some aspects, a wireless device may receive a sounding waveform via a reciprocal wireless channel. The wireless device may estimate one or more channel parameters associated with the reciprocal wireless channel based at least in part on the sounding waveform. The wireless device may generate a cryptographic key based at least in part on the one or more channel parameters associated with the reciprocal wireless channel. The wireless device may establish a secure communication session over the reciprocal wireless channel based at least in part on the cryptographic key. Numerous other aspects are provided.