Method and apparatus for authenticating a code image upon starting a device

1. A method of operating a device having an operating system, said method comprising:

storing a software image for operating the operating system in a memory of the device, said software image comprising a plurality of predetermined authentication portions determined during operating system development;

storing a first signature associated with the software image in the memory;

generating a second signature from the plurality of predetermined authentication portions of the software image less that is than a full image;

authenticating the software image by comparing the first signature from the memory and the second signature; and

executing the software image upon authentication.

2. A method as recited in claim 1 wherein the memory is a dynamic memory.

3. A method as recited in claim 2 wherein the memory comprises a non-volatile memory.

4. A method as recited in claim 1 wherein the plurality of predetermined authentication portions is spaced apart in the software image.

5. A method of operating a device comprising an operating system, said method comprising:

storing a software image for operating the operating system in a memory of the device;

grouping the software image into a plurality of predetermined different authentication portions;

storing a plurality of signatures each corresponding to a respective one of the plurality of the predetermined different authentication portions in the memory of the device;

selecting one of the plurality of the predetermined different authentication portions to form a selected portion and to form a corresponding signature from the plurality of signatures;

generating a second signature from one of the plurality of selected portions of the software image less than the a full image;

authenticating the software image by comparing the corresponding signature and the second signature; and

executing the software image upon authentication.

6. A method of operating a device comprising:

storing a software image in a memory;

grouping the software image into a plurality of authentication portions;

storing a plurality of signatures each corresponding to a respective one of the plurality of authentication portions;

randomly selecting one of the plurality of predetermined authentication portions to form a selected portion and a corresponding signature;

generating a second signature from the selected portion of the software image;

authenticating the software image using the corresponding signature and the second signature; and

executing the software image upon authentication.

7. A method as recited in claim 6 wherein the memory is a non-volatile memory.

8. A method as recited in claim 7 wherein the memory comprises read-only memory.

9. A method as recited in claim 6 wherein generating a second signature comprises generating the second signature from the plurality of predetermined authentication portions.

10. A method as recited in claim 6 wherein the plurality of predetermined authentication portions is spaced apart in the software image.

11. A method of operating a device comprising an operating system, said method comprising:

storing a software image for operating the operating system in a non-volatile memory of the device, said software image comprising a plurality of predetermined authentication portions determined during operating system development;

rebooting the device;

retrieving the software image from the non-volatile memory and a first signature associated with the software image;

storing the software image and the first signature in a dynamic memory of the device;

generating a second signature from the plurality of predetermined authentication portions of the software image less than a full image;

authenticating the software image by comparing the first signature from the dynamic memory and the second signature; and

executing the software image from the dynamic memory upon authentication.

12. A method as recited in claim 11 wherein rebooting comprises clearing the dynamic memory.

13. A method as recited in claim 11 wherein authenticating comprises authenticating when the first signature and second signature are equivalent.

14. A method as recited in claim 11 wherein the plurality of predetermined authentication portions is spaced apart in the software image.

15. A receiving unit for receiving satellite signals comprising:

an operating system;

a satellite tuner;

a memory having a software image therein, said memory having a first signature stored therein, said software image operating the operation system and said software image comprising a plurality of predetermined authentication portions determined during operating system development; and

a controller coupled to the memory and the tuner, said controller generating a second signature from the plurality of predetermined portions of the software image that is less than a full image, authenticating the software image using the first signature from the memory and the second signature, and executing the software image after authentication.

16. A receiving unit as recited in claim 15 wherein the memory comprises a flash memory.

17. A receiving unit as recited in claim 15 wherein the memory comprises a RAM.

18. A receiving unit as recited in claim 15 wherein the plurality of predetermined authentication portions are spaced apart in the software image.