Home > Articles > Security > Network Security

User Identity: Local Authentication

This sample chapter provides an overview of the basic components of successful local authentication. Topics covered include: protecting workstations, encryption of files and disks, a brief look at encryption and code-breaking in history, and the use and care of secret keys.

This sample chapter is excerpted from Authentication: From Passwords to Public Keys.

This chapter is from the book

...acting on the principle that possession was nine tenths of the law...
—Aaron Sokolski, Land Tenure and Land Taxation in America

In This Chapter

  • Workstation authentication and lock screens

  • File and disk encryption

  • Choosing and using effective encryption

  • Key handling issues

5.1 Laptops and Workstations

Patterns of sharing and access control also followed parallel evolutions. When desktop computers first appeared in offices, they were often shared. Anyone with physical access to a particular computer could do some work with it, just like researchers using the first computers in the 1950s. In the 1990s, the personal computer became an extension of the office worker's desk and file cabinet, and sharing became less common. People used the software equivalent of desk drawer locks to protect the privacy of their work in progress as well as sensitive company information.

Individual personal computers face two different threats: casual attackers and determined attackers. The casual attackers are like coworkers that might rifle through a colleague's desk uninvited—someone who takes advantage of easy access even if it violates social and ethical standards. Such people are usually deterred by relatively simple defenses. Casual attackers don't usually think of themselves as dishonest or unethical. Some people can twist the lack of defenses into an invitation: "If it was really meant to be kept secret they'd have a lock on the door, or password protect it, or something."

The earliest personal computer security mechanisms (beyond the lock on the office door) were designed to thwart casual attacks. The best known, the lock screen, grew out of a software fix for a hardware problem. Older computer screens suffered from a problem called "burn in," in which the screen's phosphor coating would wear out unevenly in response to the image it displayed. Macintosh displays that suffered from burn in, for example, would carry a faint image of the menu bar with the "apple" in the left hand corner, even if the computer and display were turned off. "Screen saver" software would detect when the computer had not been used for some period of time and then display changing patterns to prevent any single image from being burned in.

The lock screen was a security feature grafted onto the screen saver. As it was, the screen saver would essentially "take over" the computer's screen, keyboard, and mouse when it was unattended and retain control of it until the owner touched the keyboard or mouse. By adding a password, the screen saver could "lock out" anyone except the person knowing the password: this produced the lock screen mechanism.

Lock screens were soon caught up in the evolution of attacks and defenses. At first, screen savers with passwords often could be defeated by simply rebooting the computer. A few security-oriented screen savers tried to prevent this by tying themselves into the operating system so that they could retain control even if the computer was rebooted. Ultimately, the lock screen technology was built into desktop operating systems. While this prevented obvious attacks, even sophisticated lock screens remain vulnerable to fundamental attacks on personal computer hardware (see Attacks A-27, OS substitution, and A-30, I/O bus, in Section 4.2).

Determined attackers are rarely stopped by lock screens alone. A determined attacker has decided already to do something unethical or illegal, and has decided to expend personal effort on the attack. The only way to resist a determined attacker is with defenses that are too risky or costly to break down. In many cases, we can deter the attacker by making the attack visible or ensuring that it leaves a trail of evidence behind. In some cases it is enough just to detect and record the fact that the attack occurred, even if the attacker isn't identified.

More sophisticated desktop systems, notably Unix and Microsoft Windows NT or 2000, addressed the threat of more sophisticated attacks with more sophisticated access control. Unix originally had been designed as a multiuser operating system so it already incorporated the CPU-based protection mechanisms discussed in Section 4.2. Although Windows NT was designed at the outset as a personal computer operating system, the developers recognized that multiuser security features were essential to gain acceptance with major computer buyers, notably the U.S. government. These features were also incorporated into Windows 2000.

Even the Apple Macintosh system has incorporated access controls with Mac OS 9 and Mac OS X. Mac OS 9 incorporated user-based authentication and access control so that different users of a shared desktop computer could keep their files separate and, to some extent, confidential from one another. Mac OS X evolved from the Mach system, which had itself evolved from Unix and inherited Unix-like access controls.

User-based access controls, while important, are not perfect. A really motivated attacker can usually bypass these controls through a Trojan horse attack (Attack A-3 in Section 1.3). Moreover, user-based access controls on a single desktop workstation are vulnerable to the same physical attacks as lock screens.

Workstation security has achieved better results with network-based access control and with encryption. In network-based access control, the workstation's most important data resides on a server and the workstation's operator can use the data only after being authenticated. If the data resides on the workstation, then encryption is the only reliable technique to protect it, since the protection relies on knowledge of a base secret (the encryption key) and not on software defenses that attackers can bypass. The rest of this chapter examines cryptographic techniques, especially encryption and how it can provide a strong form of authentication and access control for workstation data.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020