FUSE-ENABLED SECURE BIOS MECHANISM IN A TRUSTED COMPUTING SYSTEM

An apparatus is provided for protecting a basic input/output system (BIOS) in a computing system. The apparatus includes a BIOS read only memory (ROM), a tamper detector, a random number generator, a JTAG control chain, a fuse, and an access controller. The BIOS ROM includes BIOS contents stored as plaintext, and an encrypted message digest, where the encrypted message digest has an encrypted version of a first message digest that corresponds to the BIOS contents. The tamper detector is operatively coupled to the BIOS ROM, and is configured to generate a BIOS check interrupt at a combination of prescribed intervals and event occurrences, and is configured to access the BIOS contents and the encrypted message digest upon assertion of the BIOS check interrupt, and is configured to direct a microprocessor to generate a second message digest corresponding to the BIOS contents and a decrypted message digest corresponding to the encrypted message digest, and is configured to compare the second message digest with the decrypted message digest, and is configured to preclude the operation of the microprocessor if the second message digest and the decrypted message digest are not equal. The random number generator disposed within the microprocessor, and generates a random number at completion of a current BIOS check, which is employed to set a following prescribed interval, whereby the prescribed intervals are randomly varied. The JTAG control chain is configured to program the combination of prescribed intervals and event occurrences within tamper detection microcode storage. The fuse is configured to indicate whether programming of the combination of prescribed intervals and event occurrences is to be disabled. The access control element is coupled to the fuse and the JTAG control chain, and is configured to determine a state of the fuse, and is configured to direct the JTAG control chain to disable programming of the combination of prescribed intervals and event occurrences if the fuse is blown.