Methods, systems, and devices for wireless communications are described. A wireless device may receive reference signals from another wireless device over a channel between the devices. The wireless device may perform channel estimation based on the reference signals to determine multiple taps. The wireless device may receive a message from the other wireless device indicating one or more taps to be selected to obtain a secret key for encrypting a message. The wireless device may select the taps based on the indication and communicate one or more encrypted messages with the other wireless device. For example, the wireless device may receive encrypted messages, transmit encrypted messages, or both.