Various examples are directed to systems and methods for communications security. For example, a computing device may generate a connection between the computing device and a client device. A first application executing at the computing device may send a first application session key to the client device via the connection. The first application may perform a cryptographic operation on a first message based at least in part on the first application session key to generate a first cryptographic result and send the first cryptographic result to the client device via the connection. The first application may receive a second cryptographic result from the client device via the connection and determine that the second cryptographic result was obtained with the first application session key.