Making and breaking HDCP handshakes
Suppose you connect an HDMI-compliant next-gen DVD player to an HDMI-compliant TV, and you try to play a disc. Before sending its highest-res digital video to the TV, the player will insist on doing an HDCP handshake. The purpose of the handshake is for the two devices to authenticate each other, that is, to verify that the other device is an authorized HDCP device, and to compute a secret key, known to both devices, that can be used to encrypt the video as it is passed across the HDMI cable.
At the Freedom to Tinker blog.
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