Secure internal control for encrypting video data
In one aspect, a video processing device includes a processor and a transmitter, for example implemented as separate integrated circuits on a printed circuit board. Pins on the processor are coupled to pins on the transmitter via a data channel, for example conductive leads on the printed circuit board. Video data is transmitted from the processor to the transmitter via this data channel, which is high speed enough to accommodate video data. The transmitter also includes an encryption engine used to encrypt the video data. Encryption control data, which determines the encryption to be applied, is transmitted from the processor to the transmitter over the same data channel as the video data. This is more secure than transmitting the encryption control data over a slower separate data channel, because the high speed video channel is harder to tamper with.
1. In a transmitter comprising a data receive interface having data receive pin(s), a data output interface having data output pin(s), and a control interface having control pin(s), a method for encrypting and transmitting video data, the method comprising:
receiving unencrypted video data and encryption control data from a first data channel via the data receive pin(s) of the data receive interface;
encrypting the unencrypted video data in accordance with the encryption control data;
transmitting the encrypted video data to a second data channel via the data output pin(s) of the data output interface; and
receiving control signals from a side channel that is separate from and lower speed than the first data channel via control pin(s) of the control interface, the control signals controlling at least one of said steps of receiving, encrypting and transmitting.
2. The method of claim 1 , wherein the encryption control data specifies a level of encryption used to encrypt the unencrypted video data.
3. The method of claim 2 , further comprising:
storing the level of encryption in a register, wherein encrypting the unencrypted video data comprises encrypting the unencrypted video data in accordance with the level of encryption stored in the register.
4. The method of claim 1 , wherein the encryption control data specifies whether or not to encrypt the unencrypted video data.
5. The method of claim 1 , wherein the encryption control data specifies a minimum level of encryption required to encrypt the unencrypted video data and the encrypted video data is to be transmitted to an external device via the second data channel, the method further comprising:
determining whether the external device supports the required minimum level of encryption; and
if the external device does not support the required minimum level of encryption, then not transmitting data to the external device over the second data channel.
6. The method of claim 1 , wherein:
the encryption control data includes lock/unlock instructions that specify a lock state or an unlock state for the encryption;
in a lock state, a level of encryption used to encrypt the unencrypted video cannot be changed by data received via the side channel; and
in an unlock state, the level of encryption used to encrypt the unencrypted video can be changed by data received via the side channel.
7. The method of claim 6 , further comprising:
automatically changing from a lock state to an unlock state, if no lock/unlock instruction that specifies the lock state is received during a predetermined timeout period.
8. The method of claim 1 , wherein the first data channel is at least 1000 times higher data rate than the side channel.
9. The method of claim 1 , further comprising:
transmitting status signal(s) via the control pin(s) to the side channel, the status signal(s) indicating a status of at least one of said steps of receiving, encrypting and transmitting.
10. The method of claim 9 , wherein the encryption control data specifies a level of encryption used to encrypt the unencrypted video data and the encrypted video data is to be transmitted to an external device via the second data channel, the method further comprising:
determining whether the external device supports the specified level of encryption; and
the status signal(s) transmitted via the side channel indicates whether the external device supports the specified level of encryption.
11. The method of claim 1 , wherein transmitting the encrypted video data complies with the HDMI, MHL or DisplayPort standards, and encrypting the unencrypted video data complies with the HDCP standard.
12. In a processor comprising a data transmit interface having data transmit pin(s) and a control interface having control pin(s), a method for transmitting video data and specifying encryption, the method comprising:
transmitting unencrypted video data and encryption control data to a first data channel via the data transmit pin(s) of the data transmit interface, the encryption control data determining encryption to be applied to the unencrypted video data; and
transmitting control signals to a side channel via the control pin(s) of the control interface, the side channel separate from and lower speed than the first data channel, the control signals controlling operation of a transmitter that transmits the encrypted video data.
13. The method of claim 12 , wherein the encryption control data specifies a level of encryption used to encrypt the unencrypted video data.
14. The method of claim 12 , wherein the encryption control data specifies whether or not to encrypt the unencrypted video data.
15. The method of claim 12 , wherein the encryption control data specifies a minimum level of encryption required to encrypt the unencrypted video data.
16. The method of claim 15 , wherein:
the encryption control data includes lock/unlock instructions that specify a lock state or an unlock state for the encryption;
in a lock state, a level of encryption used to encrypt the unencrypted video cannot be changed by data received via the side channel; and
in an unlock state, the level of encryption used to encrypt the unencrypted video can be changed by data received via the side channel.
17. The method of claim 12 , wherein the first data channel is at least 1000 times higher data rate than the side channel.
18. The method of claim 12 , further comprising:
receiving status signal(s) via the control pin(s) to the side channel, the status signal(s) indicating a status of the transmitter.
19. The method of claim 18 , wherein:
the encryption control data specifies a level of encryption used to encrypt the unencrypted video data;
the encrypted video data is to be further transmitted to an external device via a second data channel; and
the status signal(s) received via the side channel indicates whether the external device supports the specified level of encryption.
20. The method of claim 12 , wherein the transmitter that transmits the encrypted video data complies with the HDMI, MHL or DisplayPort standards, and the encryption determined by the encryption control data complies with the HDCP standard.