Method and system for updating a root of trust measurement function in a personal computer

The present invention relates generally to the field of computer security and particularly a method and system for securely updating a root of trust measurement.

Personal computer systems in general have attained widespread use for providing computer power to many segments of today's modern society. Personal computer systems can usually be defined as a desktop, floor standing, or portable microcomputer that comprises a system unit having a single system processor and associated volatile and non-volatile memory. FIG. 1 is an example of a conventional personal computer system 10 . The personal computer system 10 typically includes an associated display monitor 11 , a keyboard 12 , one or more diskette drives 13 and an associated printer 14 .

With the phenomenal growth and use of personal computers in the world in recent years, more and more data or information is being collected and retained or stored in such systems. Oftentimes data is sensitive in nature. As more users recognize the sensitive nature of data and its value, the more it becomes desirable to protect against such misuse. In light of this, the level, or “amount”, of security upon which a great deal of the information depended, needed to be increased. At the same time, security parameters for PC's needed to be easy to deploy, use and manage.

One of these parameters relates to the Root of Trust Measurement (RTM) function. The RTM function describes the code function that makes the first measurement of the BIOS code. Typically, it is the first module that is executed by the Basic-Input-Output System (BIOS). This is also what is referred to as the boot block. Originally, many computer security guidelines stipulated that the RTM function could not be changed under any circumstances due to the sensitive nature of the function. However, because the boot block performs other functions, such as recovery of the system in the case of a BIOS corruption issue, the RTM function may need to be updated. Recognizing this, the RTM function is now allowed to be updated, but only in a manner that ensures that the update is authentic.

Accordingly, what is needed is a method and system for securely updating the root of trust measurement function. The method and system should be simple, cost effective and capable of being easily adapted to current technology. The present invention addresses such a need.

A method and system for updating a root of trust measurement (RTM) function in a personal computer is disclosed. The RTM function is located in a boot block of the personal computer. The method and system comprise initializing a request to update the RTM function and unlocking the boot block based on an authentication process. The method and system further includes updating the RTM function.

Through the use of the method and system in accordance with the present invention, the RTM function in a personal computer is updated in a manner that ensures that the update is authentic.

FIG. 1 is an example of a typical personal computer system.

FIG. 2 shows a system in accordance with the present invention.

FIG. 3 is a high level flowchart of the method in accordance with the present invention.

FIG. 4 is a flowchart of the flash utility processing algorithm.

FIG. 5 is a flowchart of the boot block processing algorithm.

FIG. 6 is a flowchart of the POST processing algorithm.

The present invention provides a method and system for updating a root of trust measurement function in a personal computer. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is in the context of a patent application and its requirements. Various modifications to the preferred embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and features described herein.

The present invention is presented in the context of a preferred embodiment. The preferred embodiment of the present invention is a method and system for updating a root of trust measurement function in a personal computer. Through the use of the method and system in accordance with the present invention, the RTM function in a personal computer is updated in a manner that ensures that the update is authentic.

Such a method may also be implemented, for example, by operating a computer system to execute a sequence of machine-readable instructions. The instructions may reside in various types of computer readable media. In this respect, another aspect of the present invention concerns a programmed product, comprising computer readable media tangibly embodying a program of machine readable instructions executable by a digital data processor to perform a method for updating a root of trust measurement function in a personal computer.

This computer readable media may comprise, for example, RAM (not shown) contained within the system. Alternatively, the instructions may be contained in another computer readable media such as a magnetic data storage diskette and directly or indirectly accessed by the computer system. Whether contained in the computer system or elsewhere, the instructions may be stored on a variety of machine readable storage media, such as a DASD storage (e.g. a conventional hard drive or a RAID array), magnetic tape, electronic read-only memory, an optical storage device (e.g., CD ROM, WORM, DVD, digital optical tape), paper punch cards, or other suitable computer readable media including transmission media such as digital, analog, and wireless communication links. In an illustrative embodiment of the invention, the machine-readable instructions may comprise lines of compiled C, C++, or similar language code commonly used by those skilled in the programming for this type of application arts.

In many computer platforms, trusted information such as private keys, digital certificates, random number generators, protected storage and the Root-of-Trust Measurement, reside on two hardware chips within the platform, the Trusted Platform Module (TPM) and the POST/BIOS Module.

For a better understanding, please refer now to FIG. 2 . FIG. 2 shows an example of a computer platform 200 . The platform 200 comprises power supply case cards 202 , a hard disk 204 , a removable media device 206 , and a motherboard 208 . The motherboard 208 comprises Universal Serial Bus (USB) and Integrated Drive Electronics (IDE) Interfaces 210 , a central processing unit 212 , a computer memory 214 , the POST/BIOS executable code 216 , the TPM Module 218 , and a secure communications buffer 220 .

The POST/BIOS executable code 216 preferably comprises the bootblock/RTM module and the secure communications buffer 220 comprises an Erasable Electrically Programmable Read Only Memory (EEPROM) which may be locked down hard thereby requiring a reset to unlock, during the power on sequence before the operating system is started.

To further understand the method in accordance with the present invention, please refer now to FIG. 3 . FIG. 3 is a high level flowchart of the method in accordance with the present invention. First, a request to update the RTM function is initialized, via step 310 . Preferably, this request is initialized by a series of steps performed by a flash utility. Also, the update to the RTM function preferably comprises replacing the existing RTM function with a new RTM function. Next, the boot block within the POST/BIOS remains unlocked, via step 320 . Preferably, this is done after the execution of an authentication algorithm that takes place in the boot block. Finally, the RTM function is updated, via step 330 . Preferably, step 330 is accomplished via a series of steps performed by the POST code.

Although the preferred embodiment of the present invention is described in the context of being utilized in conjunction with any personal computer, one of ordinary skill in the art will readily recognize that the associated functionality could be implemented based on specified computer security guidelines while remaining within the spirit and scope of the present invention. For example, the Trusted Computing Platform Alliance (TCPA) is an open alliance formed by a small group of companies that administrate specific computer security guidelines. Accordingly, the method and system in accordance with the present invention could be implemented in accordance with TCPA guidelines.

The process begins when a flash utility makes a request to update the RTM function. For the purposes of this patent application, a flash utility comprises a remote entity that builds a file of the request on a diskette, hardfile or other suitable local storage media. Since the code for the RTM function is located in the boot block of a computer system and the boot block is normally locked to prevent tampering, the flash utility cannot directly update the RTM function. Accordingly, once the flash utility builds the file the flash utility passes the request, along with a pointer to the file, to the current boot block. Preferably, the request is passed via the secure communication buffer.

At this time the flash utility may update the remainder of the POST/BIOS using the normal processes. The computer is then rebooted. Upon reboot, the current boot block will detect the update request and will authenticate the digital signature of the POST routines used for the update. If the signature is authentic, the POST sequence will continue with the boot block unlocked. Otherwise, the boot block remains locked prior to continuing the POST sequence.

Once the POST sequence begins, the POST code will detect the update request and authenticate the request. Once the request is authenticated, the POST code will check the signature of the new RTM function. If either the request authentication or the signature check fails, the POST code will lock the boot block, report the error, and ignore the request. Once both the authenticity of the request and the validity of the new RTM function are established, the POST code will update the RTM function. Upon completion of the update, the system will reboot to force the new RTM function to execute prior to loading an operating system.

As previously articulated, the method in accordance with the present invention preferably comprises the performance of a series of steps by the flash utility, followed by the performance of a series of steps by the boot block, followed by the performance of a series of steps by the POST code. For a better understanding, please refer to FIGS. 4-6. FIG. 4 is a flowchart of the flash utility processing algorithm, FIG. 5 is a flowchart of the boot block processing algorithm and FIG. 6 is a flowchart of the POST processing algorithm.

Please refer now to FIG. 4 . First, a request to update the RTM function is detected, via step 410 . Next, the new RTM function is stored within a file on a local storage media, via step 420 . Preferably, the local storage media comprises a diskette or a hardfile. The request to update the RTM function is then passed to the boot block, via step 430 . Preferably, this request is passed to the boot block, along with a pointer to the file, via a secure communication buffer. The remainder of the POST/BIOS is then updated, via step 440 . Finally, the computer is rebooted, via step 450 .

For a more detailed understanding of the present invention, please refer now to FIG. 5 . FIG. 5 is a flowchart of the boot block processing algorithm. First, the RTM function detects the request to update the RTM function, via step 510 . Next, the digital signature of the updated POST/BIOS routines is authenticated, via step 520 . Finally, if the digital signature is authentic, the boot block remains unlocked, via 530 . It should be noted that the boot block will be locked prior to continuing the POST sequence if the digital signature is not validated.

For an even more detailed understanding of the present invention, please refer now to FIG. 6 . FIG. 6 is a flowchart of the POST processing algorithm. First, the request to update the RTM function is detected by the POST code, via step 610 . Next, the request to update the RTM function is authenticated, via step 620 . Next, the new RTM function is accessed and the digital signature thereof is verified, via step 630 . It should be noted that if either the request authentication or the signature check fails, the POST code will lock the boot block, report the error, and ignore the request. Once the digital signature is verified, the RTM function is updated with the new RTM function, via step 640 . Finally, the computer system is rebooted, via step 650 . This is done to force the new RTM function to execute prior to loading an operating system.

A method and system for updating a root of trust measurement function in a personal computer is disclosed. Through the use of the method and system in accordance with the present invention, the RTM function in a personal computer is updated in a manner that ensures that the update is authentic.

Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.