A video source application in a video source device requests from a video hardware interface of the video source device status with respect to a link linking the video source device to an external video sink device, and supplements the status request with a first basis value to a symmetric ciphering/deciphering process. The video source application, upon receiving from the video hardware interface the requested status and a verification key, generated using said symmetric ciphering/deciphering process and employing the first basis value, verifies the correctness of the verification key to determine whether to trust said provided status. In like manner, the video source application requests from the video hardware interface a secret the video hardware interface uses to cipher video to be transmitted by the video hardware interface to the external video sink device. The secret request is supplemented with a second basis value to the symmetric ciphering/deciphering process. The secret is returned in a cipher form, ciphered using a ciphering key generated using the second basis value. The video source application deciphers the secret using its own independently generated copy of the ciphering key.