Intel HDCP Authentication Linear Relation Between Keys Vulnerability
Intel's High-bandwidth Digital Content Protection (HDCP) is a specification for authentication and encryption of multimedia streams. Content encryption and authentication of a playback device are based on a public/private key pair.
Authentication is accomplished by a linear combination of private key values, based on the public key. As a direct result, being able to express an arbitrary public key as a linear combination of known public/private key pairs allows an attacker to authenticate as the arbitrary device.
This results in a large number of possible exploits, with varying degrees of computation required. As an example, an attacker able to eavesdrop on an encrypted stream may compute the shared secret, and view the decrypted content.
Although a computationally efficient algorithm has not yet been published, it may also be possible to create new, valid keys that are a linear combination of known values. Currently this may be done by enumerating all possible well formed public keys, and testing for validity.