BIOS Protection Guidelines 

for Servers (Draft)

Recommendations of the National Institute 

of Standards and Technology

Andrew Regenscheid

Special Publication 800-147B 

(Draft)
NIST Special Publication 800-147B 

(Draft) 

BIOS Protection Guidelines for Servers 

(Draft)

Recommendations of the National 

Institute of Standards and Technology

Andrew Regenscheid

Computer Security Division

Information Technology Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 

C O M P U T E R S E C U R I T Y

July 2012

U.S. Department of Commerce

Rebecca M. Blank, Acting Secretary

National Institute of Standards and Technology

Dr. Patrick D. Gallagher, Under Secretary of Commerce for 

Standards and Technology and Director
BIOS PROTECTION GUIDELINES FOR SERVERS (DRAFT)

ii

Reports on Computer Systems Technology

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BIOS PROTECTION GUIDELINES FOR SERVERS (DRAFT)

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Authority

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National Institute of Standards and Technology Special Publication 800-147B (Draft)

Natl. Inst. Stand. Technol. Spec. Publ. 800-147B, 31 pages (July 2012)

CODEN: NSPUE2

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BIOS PROTECTION GUIDELINES FOR SERVERS (DRAFT)

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Acknowledgments

The author, Andrew Regenscheid of the National Institute of Standards and Technology (NIST), wishes

to thank his colleagues who reviewed drafts of this document and contributed to its technical content. 

Abstract

Modern computers rely on fundamental system firmware, commonly known as the system Basic 

Input/Output System (BIOS), to facilitate the hardware initialization process and transition control to the 

operating system. Unauthorized modification of BIOS firmware by malicious software constitutes a 

significant threat because of the BIOS’s unique and privileged position within the PC architecture. The

guidelines in this document include requirements on servers to mitigate the execution of malicious or 

corrupt BIOS code. They apply to BIOS firmware stored in the BIOS flash, including the BIOS code, the 

cryptographic keys that are part of the root of trust for update, and static BIOS data. This guide is 

intended to provide server platform vendors with recommendations and guidelines for a secure BIOS 

update process.

Keywords

Basic Input/Output System (BIOS); information security; patch management; server security
BIOS PROTECTION GUIDELINES FOR SERVERS (DRAFT)

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Table of Contents

Executive Summary................................................................................................................. 1

1. Introduction.................................................................................................................... 1-1

1.1 Purpose and Scope................................................................................................1-1

1.2 Audience ................................................................................................................1-1

1.3 Document Structure................................................................................................1-2

2. Background .................................................................................................................... 2-1

2.1 System BIOS..........................................................................................................2-1

2.2 Server Architectures ...............................................................................................2-1

2.3 System BIOS Update Mechanisms.........................................................................2-2

2.4 Threats to the System BIOS...................................................................................2-3

2.5 Root of Trust for Update .........................................................................................2-3

3. BIOS Security Principles ............................................................................................... 3-1

3.1 BIOS Update Authentication...................................................................................3-1

3.2 Secure Local Update..............................................................................................3-1

3.3 Firmware Integrity Protection..................................................................................3-2

3.4 Non-Bypassability...................................................................................................3-2

4. Security Guidelines by Update Mechanism.................................................................. 4-1

4.1 Update Mechanism 1: Secure BIOS Update at Anytime .........................................4-1

4.2 Update Mechanism 2: Secure BIOS Update at Reboot ..........................................4-2

4.3 Update Mechanism 3: Secure BIOS Update Requiring Verification at Boot ............4-2

5. Guidelines for Service Processors ............................................................................... 5-1

5.1 Service Processor as a Root of Trust .....................................................................5-1

5.2 Non-Bypassability of BIOS Protections by Service Processor ................................5-1

List of Appendices

Appendix A— Summary of Requirements ..........................................................................A-1

Appendix B— Example of Update Mechanism 1 ................................................................B-1

Appendix C— Example of Update Mechanism 2 ................................................................C-1

Appendix D— Example of Update Mechanism 3 ................................................................D-1

Appendix E— Glossary ........................................................................................................E-1

Appendix F— Acronyms and Abbreviations....................................................................... F-1

Appendix G— References ....................................................................................................G-1
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Executive Summary

Modern computers rely on fundamental system firmware, commonly known as the system Basic 

Input/Output System (BIOS), to facilitate the hardware initialization process and transition control to the 

operating system. The BIOS is typically developed by both original equipment manufacturers (OEMs) 

and independent BIOS vendors, and is distributed to end-users by motherboard or computer 

manufacturers. Manufacturers frequently update system firmware to fix bugs, patch vulnerabilities, and 

support new hardware. This document is the second in a series of publications on BIOS protections. The 

first document, SP800-147, BIOS Protection Guidelines, was released in April 2011 and provides 

guidelines for desktop and laptop systems deployed in enterprise environments. In the future, NIST 

intends to develop a new publication providing an overview of BIOS protections for IT security 

professionals to be released as SP800-147rev1, and will reissue the current SP800-147 as SP800-147A at 

that time.

Unauthorized modification of BIOS firmware by malicious software constitutes a significant threat 

because of the BIOS’s unique and privileged position within the PC architecture. Malicious BIOS 

modification could be part of a sophisticated, targeted attack on an organization—either a permanent 

denial of service or a persistent malware presence.

This document covers BIOS protections for managed and blade servers. These types of servers contain 

Service Processors—specialized microcontrollers that provide administrators with an interface to manage 

the host server. Servers, particularly those with Service Processors, may implement multiple BIOS 

update mechanisms. Servers implementing a single BIOS update mechanism, similar to those in PC 

client systems, are expected to meet the guidelines in SP800-147.

The security guidelines in this publication do not attempt to prevent installation of unauthentic BIOSs

through the supply chain, by physical replacement of the BIOS chip, or through secure local update 

procedures. 

Security guidelines are specified for four system BIOS security features: 

• Authenticated BIOS update mechanisms, where digital signatures prevent the installation of

BIOS update images that are not authentic. 

• An optional secure local update mechanism, which requires that an administrator be physically 

present at the machine in order to install BIOS images without authentication.

• Firmware integrity protections, to prevent unintended or malicious modification of the BIOS 

outside the authenticated BIOS update process.

• Non-bypassability features, to ensure that there are no mechanisms that allow the system 

processor or any other system component to bypass the BIOS protections.

This document also provides additional information and recommendations for implementing BIOS 

protections using three BIOS update mechanisms that are commonly implemented in servers. This 

material is intended to help implementers design systems that meet the security requirements in this 

publication.

Service Processors are critical management components in many modern server designs. They are 

responsible for various management features, depending on the implementation of the system. Some, but 

not all, Service Processors are able to update the system BIOS. This document describes the possible 

roles of Service Processors in the system BIOS update process, and describes how the security guidelines 

apply to systems containing these components.
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1. Introduction

1.1 Purpose and Scope

This document provides guidelines for BIOS protections in server-class systems. It is the second in a 

series of publications on BIOS protections. The first document, SP800-147, BIOS Protection Guidelines, 

was released in April 2011 and provides guidelines for desktop and laptop systems deployed in enterprise 

environments. In the future, NIST intends to develop a new publication providing an overview of BIOS 

protections for IT security professionals to be released as SP800-147rev1, and will reissue the current 

SP800-147 as SP800-147A at that time.

Unauthorized modification of BIOS firmware by malicious software constitutes a significant threat 

because of the BIOS’s unique and privileged position within modern computer system architectures. 

Malicious BIOS modification could be part of a sophisticated, targeted attack on an organization—either 

a permanent denial of service (if the BIOS is corrupted) or a persistent malware presence (if the BIOS is 

implanted with malware).

The three core principles of BIOS protection outlined in NIST SP 800-147 for client systems—

authenticated firmware updates, integrity protection, and non-bypassability of protection mechanisms—

apply to server-class machines. However, the architectural and operational complexity in servers due to 

the need to remotely manage them makes it more difficult to implement BIOS security protections in the 

same manner as clients; the core reason for the increased difficulty is that servers typically possess 

multiple BIOS update mechanisms. In addition, some servers have one or more service processors (SPs).

SPs perform various management functions for the hosts, which may include BIOS updates. This 

introduces the SP as a security-critical component, and thus this document includes guidelines for SPs 

that are part of the BIOS update process. 

As used in this publication, the term BIOS refers to conventional BIOS, Extensible Firmware Interface 

(EFI) BIOS, and Unified Extensible Firmware Interface (UEFI) BIOS. The guidelines in this document

include requirements on servers to mitigate the execution of malicious or corrupt BIOS code. They apply 

to BIOS firmware stored in the BIOS flash memory, including the BIOS code, the cryptographic keys that 

are part of the root of trust for update (RTU), and static BIOS data. Option ROMs that are stored with the 

system BIOS firmware and are updated by the same mechanism are considered part of the BIOS for the 

purposes of this document. These guidelines do not apply to Option ROMs and firmware stored 

elsewhere in a server, such as on an option card itself.

This guide is intended to provide server platform vendors with recommendations and guidelines for a 

secure BIOS update process. System administrators should consult Section 3.2 of NIST SP 800-147 for 

recommended best practices for managing BIOS in client and server systems.

1.2 Audience

The intended audience for this document includes BIOS and platform vendors of server-class systems, 

and information system security professionals who are responsible for managing the servers’ security, 

secure boot processes, and hardware security modules. The material may also be of use when developing 

enterprise-wide procurement strategies and deployment.

The material in this document is technically oriented, and it is assumed that readers have at least a basic 

understanding of system and network security. The document provides background information to help 

such readers understand the topics that are discussed. Readers are encouraged to take advantage of other 

resources (including those listed in this document) for more detailed information. 
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1.3 Document Structure

The remainder of this document is organized into the following major sections:

 Section 2 presents an overview of the BIOS, describes server architectures and update mechanisms, 

identifies potential threats to BIOS in servers, and explains the Root of Trust for Update.

 Section 3 identifies security controls for BIOS implementations that are required or recommended to 

mitigate threats to BIOS in servers.

 Section 4 provides additional security guidelines for each of the three update mechanisms.

 Section 5 provides additional security guidelines for Service Processors in managed and blade 

servers.

The document also contains appendices with supporting material:

 Appendix A contains a summary of the security guidelines for system BIOS implementations.

 Appendices B, C, and D describe examples of possible system designs for implementing the BIOS 

protections in servers.

 Appendix E defines terms used in this document.

 Appendix F contains a list of acronyms and abbreviations used in this document.

 Appendix G contains a list of references used in the development of this document.
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2. Background

This section provides background information on the system BIOS and types of server architectures. It 

identifies the primary methods used for updating the system BIOS, and it also discusses security issues 

and threats to the system BIOS. Finally, it discusses Root of Trust for Update components.

2.1 System BIOS

Exclusive of certain configuration and security code that may be embedded into a platform’s silicon 

components, e.g. processor, the system BIOS is the first software executed on the main central processing 

unit (CPU) when a computer is powered on. While the system BIOS was originally responsible for 

providing operating systems access to hardware, its primary role on modern machines is to initialize and 

test hardware components and load the operating system. In addition, the BIOS loads and initializes 

important system management functions, such as power and thermal management. The system BIOS may 

also load CPU microcode patches during the boot process.

There are several different types of BIOS firmware. Some computers use a 16-bit conventional BIOS, 

while many newer systems use boot firmware based on the UEFI specifications [UEFI]. In this document 

we refer to all types of boot firmware as BIOS firmware, the system BIOS, or simply BIOS. When 

necessary, we differentiate conventional BIOS firmware from UEFI firmware by calling them the 

conventional BIOS and UEFI BIOS, respectively.

System BIOS is typically developed by the original equipment manufacturer (OEM) of the server.

Manufacturers frequently update system firmware to fix bugs, patch vulnerabilities, and support new 

hardware. The system BIOS is typically stored on electrically erasable programmable read-only memory 

(EEPROM) or other forms of flash memory, and is modifiable by end users. Typically, system BIOS 

firmware is updated using a utility or tool that has special knowledge of the non-volatile storage 

components in which the BIOS is stored. This tool may run on one of the CPUs in the server itself, or it 

could run on a management processor within the server chassis.

A given computer system can have BIOS in several different locations. In addition to the motherboard, 

BIOS may be found on hard drive controllers, video cards, network cards and other add-in cards. This 

additional firmware generally takes the form of Option ROMs (containing conventional BIOS and/or 

UEFI drivers). These are loaded and executed by the system firmware during the boot process. Other 

system devices, such as hard drives and optical drives, may have their own microcontrollers and other 

types of firmware.

The guidelines in this document apply to BIOS firmware stored in the BIOS flash memory, including the 

BIOS code, the cryptographic keys that are part of the root of trust for update, and static BIOS data. 

Option ROMs that are stored with the system BIOS firmware and are updated by the same mechanism are 

considered part of the BIOS for the purposes of this document. However, the guidelines do not apply to 

Option ROMs and firmware stored elsewhere in a server, such as on an option card itself.

For more information on system BIOS fundamentals, see Section 2 of NIST SP 800-147.

2.2 Server Architectures

In this subsection, we differentiate servers into three classes: Basic Servers, Managed Servers, and Blade 

Servers. The distinctions made here have to do with the mechanisms employed to update the system 

BIOS.
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A Basic Server is architecturally similar to a client PC system with a single BIOS update mechanism. 

The requirements for protecting BIOS updates for a Basic Server can be satisfied by meeting the 

requirements listed in Section 3.1 in NIST SP 800-147. Typically the Root of Trust for Update (RTU) on 

a Basic Server is part of the system BIOS (see Section 2.5 for more on RTUs). Hardware protections may 

integrate the use of a Trusted Platform Module (TPM) and chipset-based locking mechanisms. 

A Managed Server is a computer system with a dedicated management channel used for device 

maintenance and additional server management features. In addition to host processors, a Managed Server 

will have a Service Processor (see below) capable of performing system management, possibly including 

BIOS updates. It is critical to prevent the execution of malicious or corrupt code on the Service Processor 

since it has direct control over other operational aspects of the server. As a potential BIOS update 

mechanism, the code executed on the Service Processor may contain an RTU and must be protected from 

unauthorized modification.

A Blade Server is a specialized server hardware platform design that is configured as a mounted device 

in a chassis/enclosure that can be installed in a rack system. These platforms often have shared power and 

cooling and a shared management interface. Blades function either autonomously in a 

chassis/enclosure/rack as a bank of servers or they may be controlled by a central bus manager. This 

system configuration also may have multiple paths for updating the BIOS used to run the individual 

blades. From the BIOS update perspective, a Blade Server is typically similar to a managed server. 

Industry also uses the term multi-node (or modular) servers which have the same requirements as the 

Blade Servers for BIOS protections.

Managed and Blade Servers have a Service Processor, sometimes called a Baseboard Management 

Controller, which is a specialized microcontroller. The Service Processor is often a special add-in card or 

embedded on the server motherboard. The Service Processor microcontroller runs a specialized operating 

system typically stored in flash memory, and provides administrators with an interface to manage the host 

server. The Service Processor is typically a highly privileged component in modern servers, often capable 

of updating firmware and software on the system, changing configuration settings, and reading from 

system memory. This document assumes administrators will implement proper computer, network, and 

physical security controls to mitigate the unique risks to Service Processors. For instance, typically 

administrators interact with the System Processor over a network interface. Security best practices dictate 

that the Service Processor should be on a private LAN accessible only to system administrators.

Service Processors are responsible for various features, depending on the implementation of the system.

The Service Processor will typically monitor various sensors in the server, such as temperature and power 

sensors for thermal and power management. It might provide administrators with a mechanism to update 

software or firmware on the server and host operating system. Maintaining the security of the Service 

Processor is critical to maintaining the integrity and availability of the server. See Section 5 for security 

requirements for Service Processors.

2.3 System BIOS Update Mechanisms

The guidelines in this publication are intended to secure BIOS update mechanisms so that only authentic, 

authorized BIOS images are flashed. While client systems typically only have one path for updating the 

BIOS, server systems may implement several update mechanisms to allow administrators to update the 

BIOS from different environments. This publication identifies three general types of authenticated BIOS 

update mechanisms. A server will typically implement one or more of these update mechanisms. Each 

mechanism is briefly described below:
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• Update Mechanism 1 – Authenticated BIOS update that can occur anytime. This update 

mechanism allows the BIOS flash memory to be securely updated irrespective of the operating 

state of the server. This includes being able to update the BIOS while the server operates without 

requiring a reboot to update the BIOS flash. This mechanism protects against storing inauthentic 

code in the BIOS flash memory. 

• Update Mechanism 2 – Authenticated BIOS update on reboot. This BIOS update mechanism 

allows the flash process to be initiated during server runtime, but the actual update of the BIOS 

flash memory does not occur until the system reboots. This mechanism protects against storing 

inauthentic code in the BIOS flash memory.

• Update Mechanism 3 – BIOS update at runtime and verification of BIOS on reboot. With 

this BIOS update mechanism, the BIOS is verified to be authentic before it is executed on every 

boot. This mechanism would be necessary if the BIOS flash locking mechanism is inadequate to 

guarantee the integrity of a running system’s BIOS flash memory. If the BIOS flash memory is 

determined to be inauthentic during boot, an automatic recovery process is initiated and the 

inauthentic BIOS is not executed.

In addition, some servers may include a secure local update mechanism that updates the system BIOS 

without using any of the three authenticated update mechanisms discussed above. A secure local update 

mechanism ensures the authenticity and integrity of the BIOS update image by requiring that an 

administrator be physically present at the server to conduct the update. The requirement for physical 

presence mitigates the risk of remote attacks against the system BIOS.

2.4 Threats to the System BIOS

A server is susceptible to the same forms of attack that threaten a client system. Execution of operating 

system-level malware on servers could precede a BIOS attack. Server BIOS updates that are executed 

without being authenticated as coming from a trusted source are vulnerable to attacks. Since servers may 

have multiple BIOS update mechanisms, each mechanism has a risk of vulnerability. Additionally, the 

interaction between update mechanisms potentially introduces additional vulnerabilities.

The Service Processor in servers has elevated privileges to perform system management, which may 

include modifying BIOS. While the Service Processor might be controlled through an isolated 

communication channel, unauthorized access to this channel exposes great risk to the server. While many

security practices focus on the data network, the management network might be less vetted and less 

protected without special efforts.

If insufficiently protected, BIOS image backups on servers (often maintained for recovery features) are 

vulnerable to rewrite attacks even while the primary BIOS is protected from modification. Subsequent to 

successful subversion of a BIOS backup, an adversary could employ other means to cause the server to 

reboot with the infected backup image.

2.5 Root of Trust for Update

A Root of Trust for Update (RTU) is an inherently trusted combination of hardware and firmware that 

performs a secure update of the BIOS and maintains the integrity of the BIOS. The RTU may comprise 

functionality for verifying digitally signed images, engaging and disengaging write-protection 

mechanisms, writing BIOS updates to flash, performing BIOS recovery, and updating the RTU itself. 

Section 3 specifies requirements on the RTU for performing secure BIOS updates and maintaining BIOS 

integrity. The inherent trust of the RTU is derived from an isolated execution environment—minimizing 

the risk to subvert the functionality of the RTU and hence maintaining the inherent trust of the RTU.
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Each functional component of the RTU may be considered a Root of Trust for the specific function:

• Verification Component: It verifies a digitally signed image to determine if control should be 

passed to the image. This component has a trusted execution path since it is entered from a known 

good state of the machine. The verification component can be used to extend trusted execution to 

code lacking integrity protection. The verification component verifies the image and if the 

verification is successful then it passes control to the image. If the verification fails then the 

verification component returns to the trusted execution path and does not pass control to the 

image. 

• Recovery Component: It is responsible for returning the machine to a known good state. 

• Integrity Component: It is responsible for maintaining the integrity of an image. This may 

include engaging hardware and firmware based locking mechanisms to prevent unauthorized 

modification of the image. It also prevents races/logic conditions from unauthorized modification 

of an image. 

• Update Component: It is an inherently trusted combination of hardware and firmware that 

performs a secure update of the RTU and maintains the integrity of the RTU.
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3. BIOS Security Principles

The security principles presented in NIST SP 800-147 for client systems—update authentication, flash 

region integrity, and non-bypassability—apply directly to server class machines. These security principles 

are intended to mitigate advanced persistent threats targeting the system BIOS. The complexity of server 

architectures and the multiple update paths for BIOS on servers require the extension of the guidelines in 

NIST SP 800-147. This section enumerates the requirements for servers to assert the security principles 

for BIOS update. The principles use the terms authorize and authenticate in the following context. 

Authentication of an image assures the integrity and origin of the image. It is rooted at the manufacturer. 

Authentication is performed cryptographically. Authorization of an update allows the update to be 

performed. It is rooted in the system owner. 

3.1 BIOS Update Authentication

Authenticated BIOS update mechanisms shall be implemented in an RTU (see Section 2.5). These 

mechanisms employ digital signatures to ensure the authenticity of BIOS update images. The 

Verification Component of the RTU shall contain the digital signature verification algorithm and a key 

store. The key store shall include the public key needed to verify the signature of the BIOS update image 

or an approved cryptographic hash [FIPS180-3] of the key. In the case of limited storage within an RTU, 

verification of a BIOS update image may be established in two stages: (1) verification of the 

cryptographic hash of the supplied public key, and (2) verification of the signature of the BIOS update 

using the supplied public key. 

BIOS images shall be signed in conformance with NIST SP 800-89, Recommendation for Obtaining 

Assurances for Digital Signature Applications [SP800-89], using an approved digital signature algorithm

as specified in NIST FIPS 186-3, Digital Signature Standard (DSS) [FIPS186-3], that provides at least 

112 bits of security strength, in accordance with NIST SP 800-131A, Transitions: Recommendation for 

Transitioning the Use of Cryptographic Algorithms and Key Lengths [SP800-131A].

Authenticated update mechanisms shall ensure that BIOS update images have been digitally signed and 

that the digital signature can be verified using a key in the RTU before updating the BIOS. Recovery 

mechanisms should also use an authenticated update mechanism, unless the recovery process meets the 

guidelines for a secure local update.

The RTU should be capable of preventing unauthorized update of the BIOS to an earlier authentic 

version. This limitation of the rollback mechanism may be accomplished, for example, by verifying that 

the version number of the BIOS image is higher than the currently installed BIOS image’s version 

number.

3.2 Secure Local Update

Servers may optionally include a secure local update mechanism that updates the system BIOS without 

using the authenticated update mechanism. A secure local update mechanism shall ensure the 

authenticity and integrity of the BIOS update image by requiring that an administrator be physically 

present at the server to conduct the update. This requirement for physical presence mitigates the risk of a 

remote attacker conducting a malicious update to an inauthentic system BIOS image.

Interacting with a server via a remote console does not satisfy this requirement for physical presence. A 

secure local update mechanism can be used, for example, to recover from a corrupted BIOS that cannot 

be updated using an authenticated update or an automated recovery mechanism. Or, the secure local 
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update mechanism could be used by a physically-present administrator to update to an earlier BIOS 

version on a system that does not allow rollback.

3.3 Firmware Integrity Protection

To prevent the execution of inauthentic or malicious BIOS code, the integrity of the system BIOS shall be 

maintained between the verification of the system BIOS and the execution of the system BIOS during the 

boot process.

To prevent unintended or malicious modification of the system BIOS outside the authenticated BIOS 

update process, the system BIOS (excluding configuration data used by the system BIOS that is stored in 

non-volatile memory) should be protected from modifications outside the authenticated BIOS update 

mechanisms. Protection mechanisms that ensure the integrity of the system BIOS shall be engaged prior 

to execution of code outside of the RTU. BIOS integrity protections shall be enforced by hardware 

mechanisms that are disengaged only by an authorized mechanism, for example system reset.

If the system BIOS can be modified outside the authenticated BIOS update mechanisms (e.g., flash 

cannot be locked), then BIOS integrity shall be verified prior to each execution, using the Verification 

Component of the RTU to authenticate the BIOS image. If the verification fails, then the RTU shall 

automatically initiate a recovery to a protected authentic BIOS. Automatic recovery mechanisms mitigate 

the risk of a denial of service attack, whereby an attacker would load an inauthentic BIOS and put the 

system in an unbootable state.

Each RTU shall be protected from modifications outside the authenticated update mechanisms. Protection 

mechanisms that ensure the integrity of the RTU shall be engaged prior to execution of code outside of 

the RTU. RTU integrity protections shall be enforced by hardware mechanisms that are disengaged only 

by an authorized mechanism, for example system reset.

3.4 Non-Bypassability

The design of the system and accompanying system components and firmware shall ensure that there are 

no mechanisms to install and execute unauthenticated BIOS code, except through physical intervention 

and the secure local update mechanism.

In particular, the authenticated update mechanisms shall be the exclusive mechanisms for modifying the 

RTU absent physical intervention through the secure local update mechanism. The design of the system 

and accompanying system components and firmware shall ensure that there are no mechanisms that allow 

the system processor or any other system component to bypass the authenticated update mechanism for 

updating the RTU, except for the secure local update mechanism.

A modern platform includes design features that give system components direct access to the RTU or 

system BIOS for performance and management improvements, such as shadowing the BIOS in RAM or 

for system management mode operations. A system component may have read access to system flash 

memory, but it shall not be able to directly modify the RTU unless that component serves as an RTU 

itself.
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4. Security Guidelines by Update Mechanism

The following provides detailed recommendations for implementing the security guidelines in this 

document for three typical secure BIOS update mechanisms. A server may implement one or more of 

these mechanisms, and the method(s) implemented by a given server may be dictated by the hardware 

support on the platform. These methods differ on when an RTU can be established and the availability of 

a secure locking mechanism for the flash to prevent unintended or malicious modification of the code and 

data stored in the BIOS flash memory. All mechanisms depend on a digitally signed BIOS update image 

and the ability of the verification component of an RTU, using a public key, to verify the signature of that 

image.

4.1 Update Mechanism 1: Secure BIOS Update at Anytime

With this BIOS update mechanism, the secure update of the BIOS flash memory may occur during 

numerous operating states of the server. This includes being able to update the BIOS while the server 

operates without requiring a reboot of the system. While the new BIOS is not expected to execute until

reboot, the flash can be updated at runtime using a System Management Interrupt (SMI) handler, a 

Service Processor, or other secure methods. The reboot that causes the new BIOS to execute could occur 

at any later time (potentially months after the actual flash update takes place).

The relevant requirements for implementing this BIOS update mechanism are listed below:

• The BIOS update image must be digitally signed in accordance with the BIOS Update 

Authentication requirements in Section 3.1. An implementation may divide the BIOS update 

image into multiple, individually digitally signed parts.

• An RTU, as defined in Section 2.5, must be available at runtime (and may be available during 

other operating states of the server) to update the BIOS flash memory.

• A locking mechanism must exist such that only an RTU can write to the BIOS flash. Only an 

RTU should be able to unlock the flash and, when unlocked, only the RTU may have the ability 

to write to the BIOS flash memory. An RTU may always have access to write to the BIOS flash

memory.

• The digitally signed BIOS update image must be transferred to an RTU. The RTU must have the 

ability to store the BIOS update image in a location that does not allow unauthorized write access 

to the BIOS update image.

The general steps for implementing this mechanism are:

1. A digitally signed BIOS update image is transferred to the RTU.

2. The RTU stores the BIOS update image in a location that can only be written to by an RTU. 

3. The RTU verifies the BIOS update image is authentic. If the BIOS update image is determined to 

be inauthentic, the BIOS update image will not be written to the BIOS flash memory. If the BIOS 

update image is authentic, the RTU configures the locking mechanism such that only an RTU has 

access to write the BIOS flash memory. A viable locking mechanism design could allow the RTU 

to always have access to write the BIOS flash memory as long as only RTUs have the same 

capability.

4. The RTU writes the BIOS update image into the BIOS flash memory.

5. The RTU ensures that the BIOS flash memory is locked prior to transferring control to code 

outside the RTU (e.g., Option ROMs), per the Firmware Integrity Protection requirements in 

Section 3.3.

Because this secure update mechanism prevents writing inauthentic code to the BIOS flash memory, it is 

not necessary to verify the BIOS during boot.
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4-2

See Appendix B for an example of this update mechanism.

4.2 Update Mechanism 2: Secure BIOS Update at Reboot

With this BIOS update mechanism, the BIOS flash memory process is initiated at server runtime.

However, the actual update of the BIOS flash memory does not occur until a server reboot. This BIOS 

update mechanism prevents inauthentic code from ever being written to the BIOS flash memory.

The relevant requirements for implementing this BIOS update mechanism are listed below:

• The BIOS update image must be digitally signed in accordance with the BIOS Update 

Authentication requirements in Section 3.1. An implementation may divide the BIOS update 

image into multiple, individually digitally signed parts.

• A locking mechanism must exist for the BIOS flash memory such that no entity except an RTU 

has write access to the BIOS flash memory at runtime. Although it is not necessary for an RTU to 

have write access to the BIOS flash memory for this update mechanism, additional BIOS update 

mechanisms may be supported that do have this requirement.

• An RTU, as defined in Section 2.5, must be available during system boot that can update the 

BIOS flash memory. The RTU must execute on reboot before the BIOS flash memory is updated.

The RTU will verify the BIOS update image’s digital signature before any changes to the flash 

occur.

• A storage location whose contents are preserved on reboot must exist in which the signed BIOS 

update image can be buffered at runtime and which the RTU can access during the reboot to 

verify the BIOS update image’s digital signature before updating the contents of the BIOS flash 

memory. During reboot, this storage location must not be accessible by any entities other than an 

RTU.

The general steps for implementing this mechanism are:

1. A digitally signed BIOS update image is buffered into a storage location whose contents are 

preserved when the server is rebooted.

2. When the server is rebooted, execution is transferred to the RTU.

3. The RTU verifies the BIOS update image is authentic. If found to be authentic, the RTU will 

unlock the BIOS flash memory if necessary and write the update into the BIOS flash memory. If 

the BIOS update image is determined to be inauthentic, the BIOS flash memory will not be 

updated.

4. The locking mechanism for the BIOS flash memory is enabled before executing untrusted code, 

including Option ROMs. 

See Appendix C for an example of this update mechanism.

4.3 Update Mechanism 3: Secure BIOS Update Requiring Verification at Boot

With this BIOS update mechanism, a locking mechanism to protect the BIOS flash memory at runtime

does not exist or has limitations such that writes to the BIOS flash memory by an entity other than an 

RTU are not prevented. A rogue update of the BIOS flash memory might occur as the BIOS flash 

memory is not write-protected or locked. However, the contents of the BIOS flash memory shall be 

authenticated before being executed on every boot. If the BIOS flash memory is determined to be 

inauthentic during boot, an automatic recovery process to an authentic BIOS is initiated and the 

inauthentic BIOS is not executed.

The relevant requirements for implementing this BIOS update mechanism are listed below:
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• The BIOS image must be digitally signed in accordance with the BIOS Update Authentication 

requirements in Section 3.1.

• An RTU, as defined in Section 2.5, must verify the digital signature of the BIOS update image 

before writing the image to the BIOS flash memory.

• As the system BIOS is not protected from modification at runtime, the RTU must include a 

verification component capable of verifying the system BIOS prior to execution, per the 

Firmware Integrity Protection requirements in Section 3.3. The verification component must

execute on boot and verify the system BIOS before any updatable BIOS code is executed.

• If it is determined that the system BIOS is inauthentic, the RTU must initiate an automatic 

recovery process to protected and authentic system BIOS. The inauthentic system BIOS must

never be executed.

The general steps for implementing this mechanism are:

1. A digitally signed BIOS image is verified and written into the BIOS flash memory. 

2. On every boot, execution is transferred to the RTU.

3. If the verification component of the RTU determines the BIOS flash memory is authentic, 

execution is transferred to the BIOS.

4. If it is determined that the BIOS flash memory is inauthentic, the RTU initiates a recovery 

process to a protected and authentic BIOS and the inauthentic BIOS is never executed.

See Appendix D for an example of this update mechanism.
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5. Guidelines for Service Processors

A key distinction between servers and clients is the inclusion of a Service Processor in the system. The 

Service Processor plays a critical role in managing and monitoring the server, and may have a role in 

updating the system BIOS. This section describes the Service Processor and provides more detailed 

security requirements for systems that contain a Service Processor.

5.1 Service Processor as a Root of Trust

Service Processors in managed and blade servers might have the ability to directly update the BIOS flash 

memory as well as their own flash or other storage media. In these cases, some or all of the Service 

Processor environment may be employed as an RTU for the system BIOS. To maintain the integrity of 

the server firmware, the execution environment of the SP must be protected from malicious code that 

could update the BIOS or the SP flash. To comply with the BIOS security principles in Section 3, the 

Service Processor shall meet the following requirements:

1. Updates to the SP code, cryptographic keys, and static data stored on the SP flash shall be by way 

of an authenticating update mechanism.

2. The SP environment shall be controlled such that only authenticated code can be executed on the 

SP.

3. Authorization should be required for user interaction with the SP.

5.2 Non-Bypassability of BIOS Protections by Service Processor

Some servers with SPs might not employ the SP as an RTU for BIOS updates. To ensure the SP 

environment cannot bypass BIOS protections, SPs in these systems shall not have direct write access to 

the BIOS flash memory. Furthermore, the SP shall not have direct and unrestricted access to system 

memory on the server outside the control of the host operating system, to prevent the SP from interfering 

with legitimate update processes.
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Appendix A— Summary of Requirements

This appendix contains a summary of the secure BIOS update guidelines for system BIOS 

implementations found in Section 3. These guidelines are intended for platform vendors designing, 

implementing, or selecting a system BIOS implementation. Readers should consult the relevant sections 

in the main body of this document for additional informative text that further describes the intent and 

context of the guidelines.

1. BIOS Update Authentication

1-A Authenticated BIOS update mechanisms shall be implemented in an RTU (see Section 2.5). 

1-B The Verification Component of the RTU shall contain the digital signature verification 

algorithm and a key store. The key store shall include the public key needed to verify the 

signature of the BIOS update image or an approved cryptographic hash [FIPS180-3] of the key. 

In the case of limited storage within an RTU, verification of a BIOS update image may be 

established in two stages: (1) verification of the cryptographic hash of the supplied public key, 

and (2) verification of the signature of the BIOS update using the supplied public key. 

1-C BIOS images shall be signed in conformance with NIST SP 800-89, Recommendation for 

Obtaining Assurances for Digital Signature Applications [SP800-89], using an approved 

digital signature algorithm as specified in NIST FIPS 186-3, Digital Signature Standard 

[FIPS186-3], that provides at least 112 bits of security strength, in accordance with NIST SP 

800-131A, Transitions: Recommendation for Transitioning the Use of Cryptographic 

Algorithms and Key Lengths [SP800-131A].

1-D Authenticated update mechanisms shall ensure that BIOS update images have been digitally 

signed and that the digital signature can be verified using a key in the RTU before updating the 

BIOS. 

1-E Recovery mechanisms should also use an authenticated update mechanism, unless the recovery 

process meets the guidelines for a secure local update.

1-F The RTU should be capable of preventing unauthorized update of the BIOS to an earlier 

authentic version. 

2. Secure Local Update (Optional)

Servers may optionally include a secure local update mechanism, where physical presence authorizes 

installation of BIOS update images without necessarily using the authenticate update mechanisms.

2-A A secure local update mechanism shall ensure the authenticity and integrity of the BIOS update 

image by requiring that an administrator physically touch the server itself to conduct the 

update.

3. Integrity Protection

3-A The integrity of the system BIOS shall be maintained between the verification of the system 

BIOS by the RTU, and the execution of the system BIOS during the boot process.

3-B The system BIOS (excluding configuration data based by the system BIOS that is stored in 

non-volatile memory) should be protected from modifications outside the authenticate BIOS 

update mechanisms. 
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3-B.i Protection mechanisms that ensure the integrity of the system BIOS shall be engaged 

prior to execution of code outside the RTU. 

3-B.ii BIOS integrity protections shall be enforced by hardware mechanisms that are 

disengaged only by an authorized mechanism, for example system reset.

3-C If the system BIOS can be modified outside the authenticated BIOS update mechanisms, then 

BIOS integrity shall be verified prior to each execution, using the Verification Component of 

the RTU to authenticate the BIOS image. 

3-C.i If verification fails, then the RTU shall automatically initiate a recovery to a protected 

authentic BIOS. 

3-D Each RTU shall be protected from modifications outside the authenticated update mechanisms.

3-D.i Protection mechanisms that ensure the integrity of the RTU shall be engaged prior to 

execution of code outside of the RTU.

3-D.ii RTU integrity protections shall be enforced by hardware mechanisms that are 

disengaged only by an authorized mechanism, for example system reset.

4. Non-Bypassability

4-A The design of the system and accompanying system components and firmware shall ensure that 

there are no mechanisms to install and execute unauthenticated BIOS code, except through 

physical intervention and the secure local update mechanism.

4-B The authenticated BIOS update mechanism shall be the exclusive mechanism for modifying 

the RTU absent physical intervention through the secure local update mechanism.

4-C The design of the system and accompanying system components and firmware shall ensure that 

there are no mechanisms that allow the system processor or any other system component to 

bypass the authenticated update mechanism for updating the RTU, except for the secure local 

update mechanism.

4-D While a system component may have read access to system flash memory, it shall not be able 

to directly modify the RTU unless that component serves as an RTU itself.

5. Service Processors

5-A Service Processors employed as an RTU shall meet the following requirements:

5-A.i Updates to the SP code, cryptographic keys, and static data stored on the SP flash 

memory shall be by way of an authenticating update mechanism.

5-A.ii The SP environment shall be controlled such that only authenticated code can be 

executed on the SP.

5-A.iii Authorization should be required for user interaction with the SP.

5-B Service Processors that are not employed as an RTU shall be the following requirements: 

5-B.i SPs shall not have direct write access to the BIOS flash memory.

5-B.ii SPs shall not have direct and unrestricted access to system memory on the server 

outside the control of the host operating system.
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Appendix B—Example of Update Mechanism 1

Figure 1, an example system block diagram for update mechanism 1, shows the BIOS flash SPI controller 

accessible by both the host and the SP. Extra logic along the host-to-SPI controller path may be needed to 

prevent write access by the host to the BIOS flash memory. This logic may either be internal chipset 

registers or external to the chipset. Because it has write access to the system flash, the SP environment in 

this example must be a secure, closed environment as described in Section 5.

In this example, the system BIOS is given control of the host CPU at system reset. All SPI flash sectors 

are unlocked at system reset. The system BIOS, prior to allowing execution of untrusted code (e.g.,

Option ROMs, bootloaders) locks host-side write access to the system flash sectors containing the system 

SP chip

SP Ethernet

SP Processor

SPI

SP 

Firmware

(Private) 

management 

network

System 

Flash

Host 

CPU

IO Chipset System 

Ethernet

USB PCI LPC

Figure 1: Example System Block Diagram for Update Mechanism 1
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BIOS. This locking is done via interaction with the logic to “lock until reset” the sectors containing the 

BIOS image. When the lock is set, the access to this lock register becomes read-only so that the “lock 

until reset” setting itself cannot be modified. Write access to the BIOS flash sectors remains available to 

the SP.

When conducting a BIOS update, system management software on the host can interact with the SP to 

send a candidate update image to the SP. Alternatively, the BIOS update image can arrive at the SP 

through out of band communication via the SP Ethernet. The SP, as an RTU for the system BIOS, verifies 

the BIOS update image using the digital signature verification algorithm and key store on the SP. If the 

image is authenticated, then the SP, which continues to have write access to the BIOS flash memory even 

after host OS boot, can perform the flash update via interaction with the SPI controller of the BIOS flash 

memory.
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Appendix C—Example of Update Mechanism 2

Figure 2 shows an example system block diagram for a BIOS update mechanism that verifies and flashes 

BIOS update images during reboot. The BIOS flash SPI controller is accessible by just the host. A 

potential BIOS update image is stored in the SP environment. 

Figure 2: Example System Block Diagram for Update Mechanism 2

SP chip

Host 

CPU

. .

IO Chipset System 

Ethernet

SP 

Ethernet

SP Processor

SP 

Firmware

LPC

USB PCI

Video 

controller

(Private) 

management 

network

I2C

GPIO

System 

Flash

 

LPC SPI
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In this example, to initiate a BIOS update, system management software on the host can interact with the 

SP to send a BIOS update image to be stored in the SP environment for later access by BIOS.

Alternatively, the candidate BIOS update image can arrive at the SP through out of band communication 

via the SP Ethernet.

The RTU, implemented as part of the system BIOS, gets control of the host side at system reset. All SPI 

flash sectors are unlocked at system reset. Within the system flash, the RTU is not separated from the 

remainder of the system BIOS. The system BIOS, prior to executing untrusted code (e.g., Option ROMs) 

is the RTU. It communicates with the SP to check for a candidate BIOS update image. If one exists, it is 

read from the SP into host memory (which is only writable by the system BIOS during RTU execution) 

and performs verification. If the BIOS update image is authentic, the system BIOS performs the update of 

the system flash via interaction with the SPI flash controller. At completion of the BIOS update, the 

system BIOS forces a system reset and restarts execution from the new image.

If the SP indicated that no candidate BIOS update image existed, or if the candidate BIOS update image 

failed verification, BIOS locks the BIOS flash memory via SPI controller interaction to “lock until reset” 

the sectors containing the BIOS image. When the lock is set, the access to this SPI sector lock register 

becomes read-only so that the “lock until reset” setting itself cannot be modified. This sector lock is done 

prior to exiting the RTU portion of the BIOS.
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Appendix D—Example of Update Mechanism 3

An example system block diagram for update mechanism 3 shows the BIOS flash SPI controller 

accessible by both the host and the SP. Because it has write access to the BIOS flash memory, the SP 

environment in this example must be a secure, closed environment as described in Section 5.

Figure 3: Example System Block Diagram for Update Mechanism 3

In this example, to initiate a BIOS update, system management software on the host can interact with the 

SP to send a BIOS update image to the SP. Alternatively, the BIOS update image can arrive at the SP 

through out of band communication via the SP Ethernet. The SP, acting as part of the RTU, then 

authenticates the BIOS update image. If the image is authentic, then the SP, which continues to have write 

access to the system flash even after host OS boot, can then perform the flash update via interaction with 

the SPI controller of the system flash.

SP chip

Host 

CPU

. .

IO Chipset

SP Ethernet

SP Processor

SPI

SP 

Firmware

USB PCI LPC

Video 

controller

(Private) 

management 

network

I2C

GPIO

BIOS ROM 

System 

Ethernet
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In this example, the system BIOS contains its own verification component of the RTU, which 

authenticates the remainder of the system BIOS each boot. This verification component resides in the 

system flash and will be labeled the RTU-V for the purposes of describing this update mechanism. The 

RTU-V is given control of the host side at system reset. System reset also unlocks all of the SPI flash 

sectors. Within the system flash, the RTU-V is lockable, independently of the remainder of system BIOS. 

The RTU-V is also updatable as follows: Similar to update mechanism example 2, the RTU-V update 

occurs upon reboot and is updated by the RTU-V itself. It communicates with the SP to check for a 

candidate RTU-V update image. If one exists, it is read from the SP into host memory and performs 

authentication. If the image authenticates, the RTU-V does the update of the RTU-V portion of the BIOS 

flash ROM via interaction with the SPI flash controller. At completion of the RTU-V update, the RTU-V 

forces a system reset and restarts execution from the new image.

If the SP indicated that no candidate RTU-V update image existed, or if the candidate RTU-V update 

image failed verification, the RTU-V locks until reset the RTU-V sectors of the flash via interactions with 

the SPI controller.. When the lock is set, the access to this SPI sector lock register becomes read-only so 

that the “lock until reset” setting itself cannot be modified. This sector lock is done prior to exiting the 

RTU-V (e.g., before execution of the rest of BIOS).

Because the system flash regions containing BIOS code are not lockable and are subject to modification 

by malicious code, the RTU-V authenticates the remainder of system BIOS. The remainder of the system 

BIOS is kept in separate flash sectors in the system flash. If authentication passes, the RTU-V passes 

control to the remainder of the system BIOS. In this example, the remainder of system BIOS does not 

lock the flash sectors containing the remainder of the system BIOS. A possible reason for not locking the 

flash sectors may be to simplify access to those sectors by the BIOS RTU at runtime. Another possible 

reason would be that a portion of these sectors need to be writeable at runtime and the sector locking 

granularity is not sufficient to lock the BIOS without also locking the area that needs to be writeable.

If authentication of the BIOS fails, it is not executed. Instead, the RTU-V communicates with the BIOS 

RTU on the SP to inform it of the failure. The SP must then access an authentic BIOS image previously 

stored in the SP environment (possibly from the previous authenticated BIOS update), authenticate it and 

perform the flash update. The SP then forces a system reset to restart the RTU-V which will subsequently 

authenticate and execute the remainder of system BIOS.
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Appendix E—Glossary

Selected terms used in the publication are defined below.

Basic Input/Output System (BIOS): Refers collectively to boot firmware based on the conventional 

BIOS, Extensible Firmware Interface (EFI), and the Unified Extensible Firmware Interface (UEFI).

Conventional BIOS: Legacy boot firmware used in many x86-compatible computer systems. Also 

known as the legacy BIOS.

Extensible Firmware Interface (EFI): A specification for the interface between the operating system 

and the platform firmware. Version 1.10 of the EFI specifications was the final version of the EFI 

specifications, and subsequent revisions made by the Unified EFI Forum are part of the UEFI 

specifications.

Firmware: Software that is included in read-only memory (ROM).

Option ROM: Firmware that is called by the system BIOS. Option ROMs include BIOS firmware on 

add-on cards (e.g., video card, hard drive controller, network card) as well as modules which extend the 

capabilities of the system BIOS.

System Management Mode (SMM): A high-privilege operating mode found in x86-compatible 

processors used for low-level system management functions. System Management Mode is only entered 

after the system generates a System Management Interrupt and only executes code from a segregated 

block of memory.

System Flash Memory: The non-volatile storage location of system BIOS, typically in electronically 

erasable programmable read-only memory (EEPROM) flash memory on the motherboard. While system 

flash memory is a technology-specific term, guidelines in this document referring to the system flash 

memory are intended to apply to any non-volatile storage medium containing the system BIOS.

Trusted Platform Module (TPM): A tamper-resistant integrated circuit built into some computer 

motherboards that can perform cryptographic operations (including key generation) and protect small 

amounts of sensitive information, such as passwords and cryptographic keys.

Unified Extensible Firmware Interface (UEFI): A possible replacement for the conventional BIOS that 

is becoming widely deployed in new x86-based computer systems. The UEFI specifications were 

preceded by the EFI specifications.
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Appendix F—Acronyms and Abbreviations

This appendix contains a list of selected acronyms and abbreviations used in the guide.

ACPI Advanced Configuration and Power Interface

BIOS Basic Input/Output System

CPU Central Processing Unit

EEPROM Electrically Erasable Programmable Read-Only Memory

EFI Extensible Firmware Interface

FIPS Federal Information Processing Standard

FISMA Federal Information Security Management Act

GPIO General Purpose Input/Output

I2C Inter-Integrated Circuit

IO Input/Output

HTTP Hypertext Transfer Protocol

IT Information Technology

ITL Information Technology Laboratory

LAN Local Area Network

LPC Low Pin Count

NIST National Institute of Standards and Technology

OEM Original Equipment Manufacturer

OMB Office of Management and Budget

OS Operating System

PC Personal Computer

PCI Peripheral Component Interconnect

ROM Read-Only Memory

RTU Root of Trust for Update

RTU-V Root of Trust for Update verification component

SMI System Management Interrupt

SMM System Management Mode

SP Service Processor

SP Special Publication

TPM Trusted Platform Module

UEFI Unified Extensible Firmware Interface

USB Universal Serial Bus
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Appendix G—References

The list below provides references for this publication.

[DuGr09] Loïc Duflot, Olivier Grumelard, Olivier Levillain and Benjamin Morin. “ACPI and SMI 

handlers: some limits to trusted computing.” Journal in Computer Virology. Volume 6, 

Number 4, 353-374.

[EFI] EFI 1.10 Specification. Intel. 1 November 2003. http://www.intel.com/technology/efi/

[EmSp08] Shawn Embleton, Sherri Sparks, and Cliff C. Zou. "SMM Rootkits: A New Breed of OS 

Independent Malware," Proceedings of 4th International Conference on Security and 

Privacy in Communication Networks (SecureComm), Istanbul, Turkey, September 22-25, 

2008. 

[FIPS180-3] FIPS 180-3, Secure Hash Standard. October 2008.

[FIPS186-3] FIPS 186-3, Digital Signature Standard. June 2009.

[Graw09] D. Grawrock. Dynamics of a Trusted Platform: A Building Block Approach. Hillsboro, 

OR: Intel Press, 2009.

[Heas07a] J. Heasman. “Firmware Rootkits: A Threat to the Enterprise.” Black Hat DC.

Washington, DC. 28 February 2007. 

http://www.nccgroup.com/Libraries/Document_Downloads/02_07_Firmware_Rootkits_

The_Threat_to_the_Enterprise_Black_Hat_Washington_2007_sflb.sflb.ashx

[Heas07b] J. Heasman. “Hacking the Extensible Firmware Interface.” Black Hat USA. Las Vegas, 

NV. 2 August 2007. https://www.blackhat.com/presentations/bh-usa07/Heasman/Presentation/bh-usa-07-heasman.pdf

[Intel03] Intel Platform Innovation Framework for EFI- Architecture Specification v0.9. Intel.

September 2003. http://www.intel.com/technology/framework/

[KGH09] A. Kumar, G. Purushottam, and Y. Saint-Hilaire. Active Platform Management 

Demystified. Hillsboro, OR: Intel Press, 2009. 

[Sal07] Salihun, Darmawan. BIOS Disassembly Ninjutsu Uncovered. Wayne, PA: A-LIST, 2007.

[SaOr09] A. Sacco, A. Ortéga. “Persistant BIOS Infection.” Phrack. Issue 66. 6 November 2009.

http://www.phrack.com/issues.html?issue=66&id=7

[SP800-57] NIST SP 800-57, Recommendation for Key Management – Part 1: General. March 2007.

[SP800-89] NIST SP 800-89, Recommendation for Obtaining Assurances for Digital Signature 

Applications. November 2006.

[SP800-131A] NIST SP 800-131A, Transitions: Recommendation for Transitioning the Use of 

Cryptographic Algorithms and Key Lengths. January 2011.
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[Sym02] W95.CIH Technical Details. Symantec. 25 April 2002. 

http://www.symantec.com/security_response/writeup.jsp?docid=2000-122010-2655-99

[TCG05] PC Client Work Group Specific Implementation Specification for Conventional Bios 

Specification, Version 1.2. Trusted Computing Group. July 2005.

http://www.trustedcomputinggroup.org/resources/pc_client_work_group_specific_imple

mentation_specification_for_conventional_bios_specification_version_12 

[UEFI] UEFI Specification Version 2.3. Unified EFI Forum. May 2009. 

http://www.uefi.org/specs/

[Wech09] F. Wecherowski. “A Real SMM Rootkit: Reversing and Hooking BIOS SMI Handlers.”

Phrack. Issue 66. 6 November 2009.

http://www.phrack.com/issues.html?issue=66&id=11

[WoTe09] R. Wojtczuk and A. Tereshkin. “Attacking Intel BIOS.” Black Hat USA. Las Vegas, NV.

30 July 2009. http://www.blackhat.com/presentations/bh-usa09/WOJTCZUK/BHUSA09-Wojtczuk-AtkIntelBios-SLIDES.pdf