Machine instructions comprising a bootstrap code are buried within a critical
component of an electronic game console where they cannot readily be accessed or
modified. A preloader portion in a read only memory (ROM) is hashed by the bootstrap
code and the result is compared to an expected hash value maintained in the bootstrap
code. Further verification of the boot-up process is carried out by the preloader,
which hashes the code in ROM to obtain a hash value for the code. The result is
verified against a digital signature value that defines an expected value for this
hash. Failure to obtain any expected result terminates the boot-up process. Since
the bootstrap code confirms the preloader, and the preloader confirms the remainder
of the code in ROM, this technique is useful for ensuring that the code used for
booting up the device has not been modified or replaced.
