Detecting Face from an encrypted RTSP Stream using OpenCV

While using OpenCV to capture Faces from Video from IPCamera , we can use the RTSP URL to read the stream like below rtsp://user:passxx@[login to view URL] The problem is that , we can set the stream as Encrypted from IP camera console and the key is entered for decrypting the video stream. What is the best way to read encrypted stream using RTSP or any other protocol using Opencv or any other technology.