Home > Articles > Security > Software Security

  • Print
  • + Share This
This chapter is from the book

This chapter is from the book

1.5 Assurance

Trust cannot be quantified precisely. System specification, design, and implementation can provide a basis for determining "how much" to trust a system. This aspect of trust is called assurance. It is an attempt to provide a basis for bolstering (or substantiating or specifying) how much one can trust a system.

Example

In the United States, aspirin from a nationally known and reputable manufacturer, delivered to the drugstore in a safety-sealed container, and sold with the seal still in place, is considered trustworthy by most people. The bases for that trust are as follows.

  • The testing and certification of the drug (aspirin) by the Food and Drug Administration. The FDA has jurisdiction over many types of medicines and allows medicines to be marketed only if they meet certain clinical standards of usefulness.

  • The manufacturing standards of the company and the precautions it takes to ensure that the drug is not contaminated. National and state regulatory commissions and groups ensure that the manufacture of the drug meets specific acceptable standards.

  • The safety seal on the bottle. To insert dangerous chemicals into a safety-sealed bottle without damaging the seal is very difficult.

The three technologies (certification, manufacturing standards, and preventative sealing) provide some degree of assurance that the aspirin is not contaminated. The degree of trust the purchaser has in the purity of the aspirin is a result of these three processes.

In the 1980s, drug manufacturers met two of the criteria above, but none used safety seals.1 A series of "drug scares" arose when a well-known manufacturer's medicines were contaminated after manufacture but before purchase. The manufacturer promptly introduced safety seals to assure its customers that the medicine in the container was the same as when it was shipped from the manufacturing plants.

Assurance in the computer world is similar. It requires specific steps to ensure that the computer will function properly. The sequence of steps includes detailed specifications of the desired (or undesirable) behavior; an analysis of the design of the hardware, software, and other components to show that the system will not violate the specifications; and arguments or proofs that the implementation, operating procedures, and maintenance procedures will produce the desired behavior.

Definition 1–4.

A system is said to satisfy a specification if the specification correctly states how the system will function.

This definition also applies to design and implementation satisfying a specification.

1.5.1 Specification

A specification is a (formal or informal) statement of the desired functioning of the system. It can be highly mathematical, using any of several languages defined for that purpose. It can also be informal, using, for example, English to describe what the system should do under certain conditions. The specification can be low-level, combining program code with logical and temporal relationships to specify ordering of events. The defining quality is a statement of what the system is allowed to do or what it is not allowed to do.

Example

A company is purchasing a new computer for internal use. They need to trust the system to be invulnerable to attack over the Internet. One of their (English) specifications would read "The system cannot be attacked over the Internet."

Specifications are used not merely in security but also in systems designed for safety, such as medical technology. They constrain such systems from performing acts that could cause harm. A system that regulates traffic lights must ensure that pairs of lights facing the same way turn red, green, and yellow at the same time and that at most one set of lights facing cross streets at an intersection is green.

A major part of the derivation of specifications is determination of the set of requirements relevant to the system's planned use. Section 1.6 discusses the relationship of requirements to security.

1.5.2 Design

The design of a system translates the specifications into components that will implement them. The design is said to satisfy the specifications if, under all relevant circumstances, the design will not permit the system to violate those specifications.

Example

A design of the computer system for the company mentioned above had no network interface cards, no modem cards, and no network drivers in the kernel. This design satisfied the specification because the system would not connect to the Internet. Hence it could not be attacked over the Internet.

An analyst can determine whether a design satisfies a set of specifications in several ways. If the specifications and designs are expressed in terms of mathematics, the analyst must show that the design formulations are consistent with the specifications. Although much of the work can be done mechanically, a human must still perform some analyses and modify components of the design that violate specifications (or, in some cases, components that cannot be shown to satisfy the specifications). If the specifications and design do not use mathematics, then a convincing and compelling argument should be made. Most often, the specifications are nebulous and the arguments are half-hearted and unconvincing or provide only partial coverage. The design depends on assumptions about what the specifications mean. This leads to vulnerabilities, as we will see.

1.5.3 Implementation

Given a design, the implementation creates a system that satisfies that design. If the design also satisfies the specifications, then by transitivity the implementation will also satisfy the specifications.

The difficulty at this step is the complexity of proving that a program correctly implements the design and, in turn, the specifications.

Definition 1–5.

A program is correct if its implementation performs as specified.

Proofs of correctness require each line of source code to be checked for mathematical correctness. Each line is seen as a function, transforming the input (constrained by preconditions) into some output (constrained by postconditions derived from the function and the preconditions). Each routine is represented by the composition of the functions derived from the lines of code making up the routine. Like those functions, the function corresponding to the routine has inputs and outputs, constrained by preconditions and postconditions, respectively. From the combination of routines, programs can be built and formally verified. One can apply the same techniques to sets of programs and thus verify the correctness of a system.

There are three difficulties in this process. First, the complexity of programs makes their mathematical verification difficult. Aside from the intrinsic difficulties, the program itself has preconditions derived from the environment of the system. These preconditions are often subtle and difficult to specify, but unless the mathematical formalism captures them, the program verification may not be valid because critical assumptions may be wrong. Second, program verification assumes that the programs are compiled correctly, linked and loaded correctly, and executed correctly. Hardware failure, buggy code, and failures in other tools may invalidate the preconditions. A compiler that incorrectly compiles

x := x + 1

to

move x to regA
subtract 1 from contents of regA
move contents of regA to x

would invalidate the proof statement that the value of x after the line of code is 1 more than the value of x before the line of code. This would invalidate the proof of correctness. Third, if the verification relies on conditions on the input, the program must reject any inputs that do not meet those conditions. Otherwise, the program is only partially verified.

Because formal proofs of correctness are so time-consuming, a posteriori verification techniques known as testing have become widespread. During testing, the tester executes the program (or portions of it) on data to determine if the output is what it should be and to understand how likely the program is to contain an error. Testing techniques range from supplying input to ensure that all execution paths are exercised to introducing errors into the program and determining how they affect the output to stating specifications and testing the program to see if it satisfies the specifications. Although these techniques are considerably simpler than the more formal methods, they do not provide the same degree of assurance that formal methods do. Furthermore, testing relies on test procedures and documentation, errors in either of which could invalidate the testing results.

Although assurance techniques do not guarantee correctness or security, they provide a firm basis for assessing what one must trust in order to believe that a system is secure. Their value is in eliminating possible, and common, sources of error and forcing designers to define precisely what the system is to do.

  • + Share This
  • 🔖 Save To Your Account

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.

Overview


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.

Surveys

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.

Newsletters

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.

Security


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

Children


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

Marketing


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.

Choice/Opt-out


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.

Links


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