Systems and methods for detecting tampering of a computer system by calculating a boot signature

• US 20020099949A1
• Filed: 01/19/2001
• Published: 07/25/2002
• Est. Priority Date: 01/19/2001
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Fries, Robert M., Fleming, Michael K.
• Granted Patent: US 7,036,023 B2
• Time in Patent Office: Days
• US Class Current: 726/24
• CPC Class Codes: G06F 21/575 Secure boot
• CPC Class Codes: H04N 21/42623 involving specific decryption arrangements
• CPC Class Codes: H04N 21/4424 Monitoring of the internal components or processes of the client device, e.g. CPU or memory load, processing speed, timer, counter or percentage of the hard disk space used error monitoring in general G06F11/30; arrangements for monitoring conditions of receiving stations in broadcast systems H04H60/32; diagnosis, testing or measuring for television receivers H04N17/04
• CPC Class Codes: H04N 21/4432 Powering on the client, e.g. bootstrap loading using setup parameters being stored locally or received from the server resetting in general G06F1/14; program loading or initiating in general G06F9/445; bootstrapping in general G06F9/4401; secure boots of computer platforms G06F21/57
• CPC Class Codes: H04N 7/163 by receiver means only

Abstract

A computer system that contains a boot signature checker is disclosed. In one example, the boot signature checker monitors the bus connecting the processor with the memory and provides a boot signature that is a function of the signal sequence detected on the bus. If an unauthorized user tampers with the operating system within the memory as when attempting to gain unauthorized access to presentable content such as television programming, the boot signature checker will in all probability produce a different boot signature than expected. The decrypter will respond to this different boot signature by, for example, deactivating thereby potentially preventing an unauthorized user from gaining access to presentable content.

Claims

1. In a computer system configured to be capable of receiving presentable content, a method of detecting tampering of the computer system, the method comprising the following:

a specific act of booting up the computer system;

a specific act of monitoring a signal sequence that occurs internal to the computer system during the specific act of booting up the computer system;

a specific act of calculating a boot signature that is a function of the signal sequence;

a specific act of comparing the calculated boot signature to an expected boot signature that represents no tampering to the computer system; and

a specific act of determining that tampering has not occurred if the calculated boot signature is the same as the expected boot signature.

2. A method in accordance with claim 1, wherein the computer system includes a processing device and a memory device, the specific act of monitoring a signal sequence that occurs internal to the computer system during the specific act of booting up the computer system comprising the following:

a specific act of monitoring a signal sequence that occurs on a bus connecting the processing device to the memory device during the specific act of booting up the computer system.

3. A method in accordance with claim 1, further comprising the following:

a specific act of enabling presentable content to be presented if it is determined that tampering has not occurred.

4. A method in accordance with claim 3, wherein the presentable content is encrypted presentable content, wherein the specific act of enabling presentable content to be presented comprises the following:

activating a decrypter that receives the encrypted presentable content.

5. A method in accordance with claim 4, wherein the specific act of monitoring a signal sequence is performed by a boot signature checker circuit that is integrated with the decrypter.

6. A method in accordance with claim 4, wherein the specific act of activating a decrypter comprises the following:

a specific act of providing the calculated boot signature directly to the decrypter, wherein the decrypter is configured to accept the expected boot signature as a key string needed to activate the decrypter.

7. A method in accordance with claim 4, wherein the specific act of activating a decrypter comprises the following:

a specific act of providing the calculated boot signature to the decrypter; and

a specific act of the decrypter obtaining a key string needed to be activated if the calculated boot signature matched the expected boot signature.

8. A method in accordance with claim 7, wherein the specific act of the decrypter obtain a key string comprises the following:

a specific act of the decrypter obtaining the key string from the memory device.

9. A method in accordance with claim 1, further comprising the following:

a specific act of determining that tampering has occurred if the calculated boot signature is different than the expected boot signature.

10. A method in accordance with claim 9, further comprising the following:

a specific act of blocking the presentation of the presentable content if it is determined that tampering has occurred.

11. A method in accordance with claim 10, wherein the specific act of blocking the presentation of the presentable content comprises the following:

a specific act of deactivating an decrypter that receives the presentable content.

12. A method in accordance with claim 10, wherein the specific act of blocking the presentation of the presentable content comprises the following:

a specific act of disabling a demodulator such that the demodulator does not demodulate the presentable content.

13. A method in accordance with claim 10, wherein the specific act of blocking the presentation of the presentable content comprises the following:

a specific act of disabling a tuner such that the tuner does not tune to the presentable content.

14. A method in accordance with claim 10, wherein the specific act of blocking the presentation of the presentable content comprises the following:

disabling a central processing unit clock.

15. A method in accordance with claim 10, wherein the specific act of blocking the presentation of the presentable content comprises the following:

disabling a demultiplexor such that audio, video or other data cannot be extracted from the presentable content.

16. A method in accordance with claim 10, wherein the specific act of blocking the presentation of the presentable content comprises the following:

disabling a network interface device used by the computer system to interface with a network.

17. A method in accordance with claim 1, wherein the specific act of calculating a boot signature that is a function of the signal sequence comprises the following:

calculating the boot signature by applying a polynomial expression to the signal sequence.

19. A method in accordance with claim 18, wherein the step for producing a boot signature is performed by a boot signature checker that is coupled to the bus.

20. A method in accordance with claim 18, wherein the step for calculating a boot signature comprises the following:

a specific act of monitoring the signal sequence during the specific act of booting up the computer system; and

a specific act of calculating the boot signature as a function of the signal sequence monitored during the specific act of monitoring.

21. A method in accordance with claim 20, wherein the computer system includes a processing device and a memory device, the specific act of monitoring the signal sequence comprising the following:

a specific act of a boot signature checker monitoring a local bus between the processing device and the memory device to determine a signal sequence that occurs on the local bus during the specific act of booting up the computer system.

22. A method in accordance with claim 18, further comprising:

a step for acting on the determination of whether the calculated boot signature is indicative of the computer system being tampered with.

23. A method in accordance with claim 22, wherein the step for acting on the determination comprises the following:

a specific act of activating a decrypter so as to enable the decrypter to decrypt the presentable content.

24. A method in accordance with claim 23, wherein the specific act of activating a decrypter comprises the following:

a specific act of providing the calculated boot signature directly to the decrypter, wherein the decrypter is configured to accept an expected boot signature as a key string needed to activate the decrypter.

26. A computer system in accordance with claim 25, wherein the boot signature checker is directly coupled to the bus.

27. A computer system in accordance with claim 25, wherein the boot signature checker is coupled to the decrypter so as to provide the boot signature to the decrypter.

28. A computer system in accordance with claim 25, wherein the boot signature checker and the decrypter are integrated within a single physical device.

30. A computer system in accordance with claim 29, wherein the means for calculating a boot signature comprises the following:

a processing device;

a memory device;

a bus coupled to the processing device and to the memory device; and

a boot signature checker that is coupled to the bus so as to be able to monitor the bus for signal sequences.

31. A computer system in accordance with claim 30, further comprising the following:

a decrypter; and

a dedicated connection connecting the boot signature checker with the decrypter.

32. A conditional access device in accordance with claim 30, wherein the boot signature checker, the dedicated connection, and the decrypter are integrated within a single physical device.

18. In a computer system configured to be capable of capable of receiving presentable, a method of detecting tampering of the computer system, the method comprising the following:

a specific act of booting up the computer system;

a step for calculating a boot signature that is a function of a signal sequence experienced internal to the computer system during the specific act of booting; and

a step for determining whether the calculated boot signature is indicative of the computer system being tampered with.

25. A computer system capable of receiving presentable content, wherein the computer system comprises:

a processing device;

a memory device;

a bus coupled to the processing device and the memory device;

a decrypter configured to decrypt encrypted content when activated;

a boot signature checker that is coupled to the bus so as to be able to read a signal sequence asserted on the local bus during booting of the receiver,

wherein the boot signature checker is configured to calculate a boot signature that is a function of the signal sequence.

29. A computer system capable of decrypting encrypted content, wherein the receiver comprises:

a processing device;

a memory device;

a bus coupled to the processing device and the memory device;

a decrypter configured to decrypt encrypted content when activated; and

means for calculating a boot signature that is a function of the signal sequence experienced internal to the computer system during booting up of the computer system.