Method and apparatus for encrypting data transmitted over a serial link
View Patent ↗A communication system including a transmitter, a receiver, and a serial link (for example, a TMDS-like link) in which video data (or other data) are encrypted, the encrypted data are transmitted from the transmitter to the receiver, and the transmitted data are decrypted in the receiver, a transmitter and a receiver for use in such systems, a cipher engine for use in such a transmitter or receiver, a method for operating such a transmitter or receiver to encrypt or decrypt data, and a method for authenticating a receiver prior to transmission of encrypted data to the receiver over a serial link. Each transmitter, receiver, and cipher engine is configured to implement a content protection protocol in a manner that implements at least one and preferably more than one of a class of attack prevention features disclosed herein. In preferred embodiments the invention is employed to encrypt data in accordance with the High-bandwidth Digital Content Protection (“HDCP”) protocol, or a modified version of the HDCP protocol.
1. A device for use in a communication system including a transmitter, a receiver, and a serial communication link between the transmitter and the receiver, wherein the system is configured to implement a content protection protocol, wherein the protocol requires that each of the transmitter and the receiver store a set of private keys, and process the private keys together with a value received from another element of the system to generate a shared secret, and wherein said device includes:
circuitry configured to check that the private keys to be processed by at least one of the transmitter and the receiver to generate the shared secret satisfy at least one predetermined criterion, and to abort generation of the shared secret if said private keys do not satisfy each said criterion, wherein the at least one criterion specifies at least that none of the private keys consists entirely of ones, entirely of zeroes, or of an alternating pattern of ones and zeroes.
2. The device of claim 1 , wherein the at least one criterion also specifies that none of the private keys consists of at least one other simple or regular pattern of ones and zeroes.
3. A transmitter for use in a communication system including the transmitter, a receiver, and a serial communication link between the transmitter and the receiver, wherein the system is configured to implement a content protection protocol, wherein the protocol requires that each of the transmitter and the receiver store a set of private keys, and process the private keys together with a value received from another element of the system to generate a shared secret, and wherein said transmitter includes:
circuitry configured to check that the private keys that the transmitter will process to generate the shared secret satisfy at least one predetermined criterion, and to abort generation of the shared secret if said private keys do not satisfy each said criterion, wherein the at least one criterion specifies at least that none of the private keys consists entirely of ones, entirely of zeroes, or of an alternating pattern of ones and zeroes.
4. A receiver for use in a communication system including the receiver, a transmitter, and a serial communication link between the transmitter and the receiver, wherein the system is configured to implement a content protection protocol, wherein the protocol requires that each of the transmitter and the receiver store a set of private keys, and process the private keys together with a value received from another element of the system to generate a shared secret, and wherein said receiver includes:
circuitry configured to check that the private keys that the receiver will process to generate the shared secret satisfy at least one predetermined criterion, and to abort generation of the shared secret if said private keys do not satisfy each said criterion, wherein the at least one criterion specifies at least that none of the private keys consists entirely of ones, entirely of zeroes, or of an alternating pattern of ones and zeroes.