Indicating whether a system has booted up from an untrusted image

1. A computer-implemented method for indicating that a computing device has booted an untrusted image, the method comprising:

receiving, via a network, an image from a source external to the computing device;

receiving instructions, to boot up the image;

determining whether the source external to the computing device is a trusted source, wherein determining comprises the steps of:

retrieving a digital signature appended to the image,

decrypting the digital signature using a cryptographic key, and

comparing the decrypted digital signature with a message digest computed based on the image;

permanently setting, if the image is not from a trusted source, an indicator to indicate that the computing device has booted from an untrusted image, the indicator implemented as a trusted platform module (TPM) chip configured to be permanently written to once, such that the indicator cannot be rewritten;

booting the image;

sending a request for accessing at least one resource;

receiving, from an entity controlling access to the at least one resource, a request for an indicator status; and

providing the entity with the indicator status, wherein the entity is configured to restrict access to the at least one resource if the indicator status indicates that an untrusted image has been booted by the computing device.

2. The computer-implemented method of claim 1 , wherein the indicator is located on a processor of the TPM chip.

3. The computer-implemented method of claim 1 , wherein the indicator comprises a microfuse.

4. The computer-implemented method of claim 3 , wherein setting the indicator comprises burning the microfuse.

5. The computer-implemented method of claim 1 , wherein setting the indicator comprises permanently burning the TPM chip to a state indicating that the computing device has booted an untrusted image.

6. The computer-implemented method of claim 1 , wherein the indicator comprises a Write Once, Read-Many (WORM) memory device.

7. A computing device comprising:

one or more processors;

a trusted platform module (TPM) chip configured to be permanently written to and comprising an indicator; and

a machine-readable medium comprising instructions stored therein, which when executed by the one or more processors, cause the processors to perform operations comprising:

receiving, via a network, an image from a source external to the computing device;

receiving instructions to boot from the image;

determining whether the source external to the computing device is an untrusted source, wherein determining comprises the steps of:

retrieving a digital signature appended to the image,

decrypting the digital signature using a cryptographic key, and

comparing the decrypted digital signature with a message digest computed based on the image;

permanently setting, if the image is from an untrusted source, the indicator to indicate that the computing device has booted an untrusted image, the indicator configured to be permanently written to once, such that the indicator cannot be rewritten;

booting the image;

sending a request for accessing at least one resource;

receiving, from a process controlling access to the at least one resource, a request for an indicator status; and

providing the process with the indicator status, wherein the process is configured to restrict access to the at least one resource if the indicator status indicates that an untrusted image has been booted by the computing device.

8. The computing device of claim 7 , wherein the indicator is a Write-Once, Read-Many (WORM) memory device.

9. The computing device of claim 8 , wherein the WORM memory device is a microfuse.

10. The computing device of claim 9 , wherein setting the indicator comprises burning the microfuse.

11. The computing device of claim 7 , wherein the indicator is located on a processor of the TPM chip.

12. The computing device of claim 7 , wherein setting the indicator comprises permanently burning the TPM chip to a state indicating that the system has booted an untrusted image.

13. The computing device of claim 7 , wherein the indicator comprises a lockable memory space of the TPM.

14. A non-transitory machine-readable medium comprising instructions stored therein, which when executed by a machine, cause the machine to perform operations comprising:

receiving, via a network, an image from a source external to the machine;

receiving instructions to boot from the image;

determining that the source external to the machine is untrusted, wherein determining comprises the steps of:

retrieving a digital signature appended to the image,

decrypting the digital signature using a cryptographic key, and

determining that the decrypted digital signature and a message digest computed based on the image do not match;

permanently setting an indicator implemented as a trusted platform module (TPM) chip to indicate that the machine has booted an untrusted image by permanently writing the TPM chip to a state indicating that the machine has booted the untrusted image, the indicator configured to be permanently written to once, such that the indicator cannot be rewritten;

booting the image after setting the indicator;

sending a request for accessing at least one resource;

receiving, from a process controlling access to the at least one resource, a request for an indicator status; and

providing the process with the indicator status, wherein the process is configured to restrict access to the at least one resource if the indicator status indicates that an untrusted image has been booted by the machine.