As part of his ongoing series on the failings in the HDCP video crippleware being build into HD TVs, video-game consoles and PCs, Princeton engineering prof Ed Felten describes how easy it is to subvert the system:
…[I]t has a very large problem: if any [forty] devices conspire, they can break the security of the system.
To see how, let's do an example. Suppose that Alice, Bob, Charlie, and Diane conspire, and that the conspiracy wants to figure out the secret vector of some innocent victim, Ed. Ed's addition rule is "+", and his secret vector is, of course, a secret.