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The term computer security is used frequently, but the content of a computer is vulnerable to few risks unless the computer is connected to other computers on a network. As the use of computer networks, especially the Internet, has become pervasive, the concept of computer security has expanded to denote issues pertaining to the networked use of computers and their resources.

The major technical areas of computer security are usually represented by the initials CIA: confidentiality, integrity, and authentication or availability. Confidentiality means that information cannot be access by unauthorized parties. Confidentiality is also known as secrecy or privacy; breaches of confidentiality range from the embarrassing to the disastrous. Integrity means that information is protected against unauthorized changes that are not detectable to authorized users; many incidents of hacking compromise the integrity of databases and other resources. Authentication means that users are who they claim to be. Availability means that resources are accessible by authorized parties; "denial of service" attacks, which are sometimes the topic of national news, are attacks against availability. Other important concerns of computer security professionals are access control and nonrepudiation. Maintaining access control means not only that users can access only those resources and services to which they are entitled, but also that they are not denied resources that they legitimately can expect to access. Nonrepudiation implies that a person who sends a message cannot deny that he sent it and, conversely, that a person who has received a message cannot deny that he received it. In addition to these technical aspects, the conceptual reach of computer security is broad and multifaceted. Computer security touches draws from disciplines as ethics and risk analysis, and is concerned with topics such as computer crime; the prevention, detection, and remediation of attacks; and identity and anonymity in cyberspace.

While confidentiality, integrity, and authenticity are the most important concerns of a computer security manager, privacy is perhaps the most important aspect of computer security for everyday Internet users. Although users may feel that they have nothing to hide when they are registering with an Internet site or service, privacy on the Internet is about protecting one's personal information, even if the information does not seem sensitive. Because of the ease with which information in electronic format can be shared among companies, and because small pieces of related information from different sources can be easily linked together to form a composite of, for example, a person's information seeking habits, it is now very important that individuals are able to maintain control over what information is collected about them, how it is used, who may use it, and what purpose it is used for.

Scope of this Guide

This guide is intended to present a selected list of sites that cover the basic issues of computer security and which provide useful information for the non-expert (librarian, undergraduate student, office manager, etc.) who wants to learn more about this increasingly important subject. The categories are intended to offer points of departure for some of the many aspects of computer security. For the sake of brevity, this guide stops short of entering the vast realm of commercial software products, consulting firms, and the like. The individual who is in the market for security products or services should have no trouble finding descriptions, reviews, and comparisons on the web and through other media.

Methods

The web sites in this list were collected through various methods, including searches of Internet directories such as Google and Yahoo, the Librarian's Index to the Internet, the {Scout Report}, and the World Cat database (userid and password are required); burrowing through information security portals such as {InfoSysSec} and Packet Storm Security; and exploring links from within quality sites as they were encountered. Emphasis has been placed on sites that provide practical information rather than merely advertise products; accordingly, most of the sites selected are hosted in .edu, .gov, and .org domains. However, commercial sites were not discounted if they provided substantive information in addition to product information.

General Sources

Center for Education and Research in Information Assurance and Security



CERIAS's mission is to be recognized as the leader in information security and assurance research, education, and community service. To these ends, CERIAS offers a free security seminar on diverse security topics on Wednesday afternoons during the fall and spring semesters; attendees may show up in person or through a live internet stream. The CERIAS web site also includes extensive computer security resources for K-12 teachers, including background information, lesson plans, and links to other web resources.

TECS: The Encyclopedia of Computer Security



TECS provide a forum for visitors to seek the opinions of one or several security experts on a broad scope of security questions. Users range from individuals asking about their home computers to students working on projects to IT professionals; TECS's panel of volunteer security experts tend to work for computer or security consulting companies. Questions are sent via listserv to the experts, whose answers are then published, along with the question, on the web site. The site owners request that the experts try to provide balanced answers that do not gratuitously advertise specific products; vendors are free to list full product descriptions in the TECS Security Product Database.

CYBERCRIME



This site is maintained by the Computer Crime and Intellectual Property Section (CCIPS) of the Criminal Division of the U.S. Department of Justice; the information available at this site is presented from a legal, rather than technical, perspective. It provides a plethora of information about the various ways computers can be used to commit crimes, how and to whom to report computer crimes, and what to do if you are the victim of computer crime. It includes links to cases, laws, legal issues, and policy issues surrounding hacking, intellectual property infringements, and other online offenses.

Common Vulnerabilities and Exposures



MITRE, a not-for-profit national resource that provides systems engineering, research and development, and information technology support to the government, has created CVE in an attempt to standardize the names of vulnerabilities and other information security exposures. MITRE's goal is to increase data communication across network tools by encouraging software companies and developers to use the common names found at the CVE web site; according to CERIAS, "CVE is the key to vulnerability database compatibility." To date, over 60 major organizations have agreed to make their products and services CVE compliant.

Stay Safe Online



The National Cyber Security Alliance, comprised of corporate and government organization members, sponsors Stay Safe Online to educate home and small business computer users in basic computer security practices, thereby helping to protect the nation's internet infrastructure. The site offers a personal computer security self-test, beginner's guides on various security topics, and a one-hour online course on security fundamentals.

Security Statistics



Because online banks, retailers, and other businesses may wish to protect their reputations by not reporting problems associated with online attacks, statistics about such can be difficult to find. The Security Statistics site is a portal to data on computer security incidents. Statistics are pooled from a wide range of sources, and includes information about security spending, known vulnerabilities, numbers of reported security breaches, economic impact of incidents, arrests and convictions, and more. The site does not guarantee the accuracy of reported statistics, but the sources of each statistic are included.

Ethics

Computer and Information Ethics on WWW



This site is a subdivision of a website on ethics resources which is maintained by the University of British Columbia's Centre for Applied Ethics. The site provides lists of web sites, as well as lists of electronic and print publications, pertaining to various ethical issues in computing. There is a section on courses in computer ethics, which provides links to online syllabi to classes taught at other institutions, and a list of links to relevant organizations. The breadth of this site is limited, but it's a good place to begin exploring the ethical issues of network computing.

Ethics in Computing

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This site is administered by Dr. Edward F. Gehringer, an NCSU professor in Electrical & Computer Engineering and Computer Science who teaches several undergraduate and graduate classes in computer science and computer ethics. The site organizes computer ethics into a simple hierarchy of topics, starting with basic information on ethics. The articles are not necessarily recent, although many concepts pertaining to ethics may remain constant over time. An interesting feature is the site map, which looks like a real map, which offers a graphical representation of how the concepts are related.

Privacy

EFF Privacy Now! Campaign

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The Electronic Frontier Foundation was founded in 1990 to confront civil liberties issues raised by new technologies. EFF's interest in privacy issues runs the gamut from Internet anonymity and pseudonymity to medical privacy to the privacy risks posed by the nation's post-9/11 increased interest in surveillance, biometrics, and a national identification system. This site goes beyond mere tips and offers a thoughtful analysis of the privacy (and social) consequences of our increasingly automated society. Look for Carabella-an interactive adventure game that illustrates some of the privacy and fair use issues associated with online music shopping.

Privacy Rights Clearinghouse



The Privacy Rights Clearinghouse is a nonprofit consumer advocacy organization. Their web site is full of information on privacy rights in an online environment. The main issues addressed on this site include personal privacy, financial privacy, and identity theft. Information sources include fact sheets covering specific privacy issues, news items and articles about privacy, and transcripts of PRC speeches and testimony from conferences and legislative hearings.

The Privacy Foundation

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The Privacy Foundation's main privacy concerns are data that is collected surreptitiously by companies about web surfers and their browsing habits, and employer surveillance of computer activity in the workplace. Users can sign up for free email delivery of the Foundation's TipSheets and Privacy Watch advisories and commentaries. An interesting free download available at this site is Bugnosis, software which alerts Internet Explorer users to web bugs, tiny or invisible web page graphics that have been encoded to collect information about who is browsing the web page.

Platform for Privacy Preferences (P3P) Project



The Worldwide Web Consortium, an organization promoting greater interoperability for web technologies, has developed P3P, a proposed standard that allows web sites to state their privacy policies using special keywords so that other P3P-enabled utilities (e.g., web browsers) can interpret them and compare them to a user's privacy preferences. P3P offers users greater control over how their personal information might be used on the Internet by giving them more opportunities to avoid offending sites.

Consumer Information

Better Business Bureau Online



The Better Business Bureau system, which extends over most of the United States and Canada, has for many years mediated consumer problems by advocating voluntary self-regulation for businesses combined with increased education for consumers. The BBB now extends its services to the e-commerce arena, offering a BBB seal of reliability for qualified businesses to place on their web sites. For consumers, BBBOnline offers a "safe shopping list" of companies which merit the BBB's seal, as well as information on web safety and privacy, and online forms for lodging complaints.

Shopping Safely Online



The National Consumer League offers Shopping Safely Online as part of its larger web site of general consumer information. In addition to online shopping tips, this site provides "e-ssentials" of online privacy and security for the consumer, and advice for using online auctions. Shopping Safely Online provides a link to the NCL's National Fraud Information Center, where users can report suspected fraud and access a wealth of other sources about the risks of doing business online.

Internet Fraud Complaint Center

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The IFCC, a partnership between the FBI and the National White Collar Crime Center, offers this web site as a place for consumers to learn about Internet fraud, which is largely comprised of incidents relating to online auctions, credit card misuse, and other consumer-related activity. The site provides an easy-to-complete form for reporting Internet fraud. Of special interest is the IFCC's annual report on the numbers, types, and economic impacts of crimes reported through the site.

Kids

NetzSmartz Workshop



This site is published by the National Center for Missing and Exploited Children. Through games and other online activities, it introduces kids to some of the "outlaws of Webville," and instructs kids on how to respond to inappropriate behavior they might encounter online. The Netsmartz site for parents and educators provides suggestions for online and offline activities and is designed to increase communication between parents and children about Internet safety.

CyberSmart!

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The CyberSmart! School Program is a non profit corporation that advocates Internet education by empowering children rather than simply monitoring them. The CyberSmart web site provides brief lessons for teens, printable color posters for parents to hang near the family computer, and a curriculum of 65 standards-based lesson plans for K-8 teachers. The curriculum is centered around the SMART model, focusing on safety, manners, advertising, research, and technology. Lessons plans have been designed to stand alone, can be taught in any order, and can be taught by a technology teacher, librarian or media specialist, or science or social studies teacher as appropriate for the subject matter.

Antivirus

Virus Bulletin



Virus Bulletin is a fee-based, monthly magazine that provides information, reviews, and comparisons of antivirus products. The Virus Bulletin website offers the latest virus-related news, description of recent viruses, and monthly prevalence tables of known virus activity. Consumers can see which antivirus products have earned the VB100% award, which is awarded to products that detect all In The Wild Viruses (see WildList Organization, below) in test scans. Of particular practical use are four step-by-step DOS tutorials for recovering from some of the more common problems of virus infection.

The WildList Organization International



The WildList Organization's mission is "to provide accurate, timely and comprehensive information about 'In the Wild' computer viruses to both users and product developers." "In the wild" viruses are viruses that have been cited by two or more of the organization's panel of computer experts as spreading in the real world and therefore pose a real threat to computers and networks. The WildList is made available free of charge by the organization and is considered a standard against which the effectiveness of antivirus programs is measured. The WildList Organization has retained its independence from any one antivirus developer and encourages all users to find an antivirus vendor and develop a relationship with its customer support service.

Hoax Busters

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Hoax Busters is a public service of the Department of Energy's Computer Incident Advisory Capability (CIAC). Hoax Busters posits that dealing with hoax emails is annoying and time-consuming at best, and costly at worst. The Hoax Busters web is a clearinghouse of information about various types of Internet hoaxes, and strives to debunk dire warnings about various fake viruses and other malicious code that have no basis in fact. The site also confronts chain letters, urban myths, sympathy letters, and other cons, and offers suggestions for how to recognize hoaxes and what to do about them.

F-Secure: Security Information Center



The self described "industry standard source for up-to-date information on new viruses and hoax alerts," this site provides long, easily readable descriptions and screen shots of known viruses, including their variations, and information on how to recover if you're hit. While F-Secure naturally promote the sale of their commercial products, they also offers a few dozen free downloads to fix specific virus problems. Also of interest are a six-minute video entitled "Virus Summary 2001," an account of the most notable (i.e., destructive) virus attacks of 2001, and a list of tips to avoid those pesky, and increasingly popular, email worms.

Security Policies

Security Policy Issues

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The Systems Administration, Networking, and Security Institute (SANS) is an organization comprised of computer security practitioners from government agencies, corporations, and universities. The SANS reading room provides access to over 1300 research articles across the spectrum of computer security; the Security Policy Issues section features over 60 articles, many of which were written by IT professionals to fulfill part of the requirements for the Global Information Assurance Certification. This site also contains an information security policy primer and policy examples and templates. Access to the SANS reading room is free, but users must register to receive a password.

EDUCAUSE/Cornell Institute for Computer Policy and Law



The ICPL is a collaboration between Cornell, which began its Computer Policy and Law program in 1996, and EDUCAUSE, which promotes intelligent use of information technology in higher education. The Library Resources section provides access to hundreds of computer policies collected from educational institutions of all sorts, companies and corporations, networks, and municipalities. The policies pertain to virtually every aspect of campus technology use, from acceptable/responsible use to library policies to security and privacy policies. Users are invited to submit their own policies to the collection.

Cryptography

Cryptology ePrint Archive



The International Association for Cryptologic Research (IACR) is a non-profit scientific organization whose purpose is to further research in cryptology and related fields. IACR's Cryptology ePrint Archive accepts clear and readable submissions from authors which "look somewhat new and interesting," and "contain proofs or convincing arguments for any claims." The archive begins in 1996, and as of this writing, there are 136 articles posted for 2002. While many of the newer articles are available as .pdf files, many files are available in postscript format only.

The International PGP Home Page



Pretty Good Privacy (PGP) is a cryptographic device for protecting digital information, including the contents of email messages, developed by Phil Zimmerman in 1991 and distributed as freeware for non-commercial use. The purpose of this web site is to promote the use of PGP worldwide by providing downloads, documentation, FAQs, lists of known bugs, links to web sites, and the latest news and other information about PGP in English and other languages.

Intrusion Detection

DShield-Distributed Intrusion Detection System



collects information about cracking, or penetration of computer systems by unauthorized parties, from all over the Internet. Systems administrators are encouraged to share their firewall logs so that patterns of intrusion activity can be analyzed; Dshield will contact an Internet service provider if it appears to be the origin of suspicious activity. Dshield provides a geographic distribution of reported attack sources from the past five days, as well as the IP addresses of the 10 most probed ports and the top 10 offending ports. The site also provides an "Are you cracked?" utility, which compares the user's IP address with a list of known attackers; if an IP address is matched, it is possible that the user's computer has been used by crackers to attack other machines.

Operating System Security

Network Security Library

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This is a site providing articles on general network and system security, and no emphasis is placed on any one OS. Due to the large number of articles available on Unix and Windows, these systems have their own links; articles on other operating systems, such as Macintosh or Linux, can be found through keyword searches. Articles come from a variety of sources, including individual submissions as well as published book chapters. Readers are invited to rate articles on a scale of one to ten, and the average score and number of votes are listed with each article title.

Windows Security Guide



This site lists security vulnerabilities and fixes for all Microsoft operating systems, as well as for network-related utilities such as MS Internet Explorer and Internet Information Server. Other services include a free newsletter of alerts and updates, and "support forums" for discussion of security topics. There are two levels of membership: the basic free membership allows access to the forums and newsletters, while a fee-based premium subscription option allows access to help files, free downloads, and the ability to turn off advertisements.

Macintosh Security Site



The Macintosh Security Site contains several informative articles on Macintosh security, and reviews of many security products for Macs and Mac servers. While the site is supported through paid advertisements, the ads are rather unobtrusive. Of interest is the fact the Macintosh Security Site is maintained as the "white side" of Freak's Macintosh Archive, a "hacking" site devoted to announcing and exploiting security vulnerabilities in Macintosh software & utilities.

Linux Security



This site is sponsored by Guardian Digital, Inc., an Open Source security company which produces EnGarde Linux products. The site is not used solely to advertise EnGarde products, and other vendors and products are represented through their sponsorship of the site as well as in articles and advisories posted at the site. The News section of the site provides full-text articles, reprinted from a variety of external sources, on a wide range of general and Linux-specific security topics; the Documentation section features numerous practical "how-to" articles. Users can subscribe to free weekly Linux security newsletters and advisories and participate in an online mailing list.

Certification

CISSP and SSCP Open Study Guides



The International Information Systems Security Certification Consortium, Inc () offers two security certifications, the Certified Information Systems Security Professional (CISSP) and the Systems Security Certified Practitioner (SSCP). This site offers study guides, tips for taking the certification tests, newsletters, chat rooms, book reviews, and more, all written by volunteers who are preparing for or have passed the exams. Study guides address particular sections included in the exams. Free registration is required to access the full content of this site.

Information Warfare

Information Warfare Site



Because of the increasing interconnectedness of critical systems such as telecommunications, banking and finance, energy, and transportation, national infrastructures have become increasingly vulnerable to online terrorist threats. The Information Warfare Site "aims to stimulate debate about a range of subjects from information security to information operations and e-commerce." While the site's domain name denotes United Kingdom, much of the content is derived from government and news sources of the United States and other countries. Online discussion forums cover topics such as e-commerce, terrorism, critical infrastructure protection, and others.

Biometrics

Biometrics Research



This site, run by Michigan State University's Department of Computer Science and Engineering, is a good beginning point for learning more about biometrics. It includes a brief but informative overview of biometrics, and descriptions of various biometric technologies, such as fingerprint matching, hand geometry, voice recognition, and so on. The "Projects" and "Publications" lists are limited to work by MSU people, but there is also a short list of external web links leading to biometric companies, consulting firms, and research centers.

International Biometric Group



International Biometric Group LLC is a biometrics consulting firm which considers itself to be "vendor-independent and technology-neutral, allowing it to objectively and independently assess companies, technologies, products, and projects." Of special interest at IBG's web site is the "Research and Reports" section, where IBG provides information on biometrics basics, specific biometric technologies and their applications, accuracy and performance, as well as vendor and industry information. Users must register with the site to gain access to the full reports, but registration is free and is activated immediately.

Biometrics Catalog



This is a database of biometric technologies maintained by the U.S. Department of Justice. Users can search for information about biometric products by biometric type, keyword, and date, as well as vendor category (commercially available products, products in government testing, products in non-government testing, etc.). Vendors can add information about their products, but forms that do not contain complete contact information will not be posted to the site.

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Computer security is a branch of information security applied to both theoretical and actual computer systems. [pic]Computer security is a branch of computer science that addresses enforcement of 'secure' behavior on the operation of computers. The definition of 'secure' varies by application, and is typically defined implicitly or explicitly by a security policy that addresses confidentiality, integrity and availability of electronic information that is processed by or stored on [pic]computer systems. The traditional approach is to create a trusted security [pic]kernel that exploits special-purpose hardware mechanisms in the microprocessor to constrain the [pic]operating system and the application programs to conform to the security policy. These systems can isolate processes and data to specifier domains and restrict access and privileges of users. This approach avoids trusting most of the [pic]operating system and applications. In addition to restricting actions to a secure subset, a secure system should still permit authorized users to carry out legitimate and useful tasks. It might be possible to secure a computer against misuse using extreme measures:

|“ |The only truly secure system is one that is powered off, cast in a block of concrete and sealed in a lead-lined |” |

| |room with armed guards - and even then I have my doubts. | |

Eugene H. Spafford, director of the Purdue Center for Education and Research in Information Assurance and Security. [1]

It is important to distinguish the [pic]techniques used to increase a system's security from the issue of that system's security status. In particular, systems which contain fundamental flaws[1] in their security designs cannot be made secure without compromising their usability. Most [pic]computer systems cannot be made secure even after the application of extensive "[pic]computer security" measures. Furthermore, if they are made secure, functionality and ease of use often decreases. Computer security can also be seen as a subfield of security engineering, which looks at broader security issues in addition to [pic]computer security.

|Contents |

|[hide] |

|1 Secure operating systems |

|1.1 Security by design |

|1.1.1 Early history of security by design |

|1.2 Secure coding |

|1.3 Terms |

|1.4 Capabilities vs. ACLs |

|1.5 See also |

|1.6 Notes |

|1.7 References |

|1.8 Further reading |

|1.9 External links |

[pic]Secure operating systems

One use of the term [pic]computer security refers to technology to implement a secure operating system. Much of this technology is based on science developed in the 1980s and used to produce what may be some of the most impenetrable operating systems ever. Though still valid, the technology is almost inactive today, perhaps because it is complex or not widely understood. Such ultra-strong secure operating systems are based on operating system kernel technology that can guarantee that certain security policies are absolutely enforced in an operating environment. An example of such a Computer security policy is the Bell-LaPadula model. The strategy is based on a coupling of special microprocessor hardware features, often involving the memory management unit, to a special correctly implemented [pic]operating system kernel. This forms the foundation for a secure operating system which, if certain critical parts are designed and implemented correctly, can ensure the absolute impossibility of penetration by hostile elements. This capability is enabled because the configuration not only imposes a [pic]security policy, but in theory completely protects itself from corruption. Ordinary operating systems, on the other hand, lack the features that assure this maximal level of security. The design methodology to produce such secure systems is precise, deterministic and logical. Systems designed with such methodology represent the state of the art of [pic]computer security and the capability to produce them is not widely known. In sharp contrast to most kinds of software, they meet specifications with verifiable certainty comparable to specifications for size, weight and power. Secure operating systems designed this way are used primarily to protect national security information and military secrets. These are very powerful security tools and very few secure operating systems have been certified at the highest level (Orange Book A-1) to operate over the range of "Top Secret" to "unclassified" (including Honeywell SCOMP, USAF SACDIN, NSA Blacker and Boeing MLS LAN.) The assurance of security depends not only on the soundness of the [pic]design strategy, but also on the assurance of correctness of the implementation, and therefore there are degrees of security strength defined for COMPUSEC. The Common Criteria quantifies security strength of products in terms of two components, security capability (as Protection Profile) and assurance levels (as EAL levels.) None of these ultra-high assurance secure general purpose operating systems have been produced for decades or certified under the Common Criteria.

Security by design

The technologies of [pic]computer security are based on logic. There is no universal standard notion of what secure behavior is. "Security" is a concept that is unique to each situation. Security is extraneous to the function of a computer application, rather than ancillary to it, thus security necessarily imposes restrictions on the application's behavior. There are several approaches to security in computing, sometimes a combination of approaches is valid:

Trust all the software to abide by a [pic]security policy but the software is not trustworthy (this is computer insecurity).

Trust all the software to abide by a [pic]security policy and the software is validated as trustworthy (by tedious branch and path analysis for example).

Trust no software but enforce a [pic]security policy with mechanisms that are not trustworthy (again this is computer insecurity).

Trust no software but enforce a [pic]security policy with trustworthy mechanisms.

Many systems unintentionally result in the first possibility. Approaches one and three lead to failure. Since approach two is expensive and non-deterministic, its use is very limited. Because approach number four is often based on hardware mechanisms and avoid abstractions and a multiplicity of degrees of freedom, it is more practical. Combinations of approaches two and four are often used in a layered architecture with thin layers of two and thick layers of four. There are myriad strategies and techniques used to [pic]design security systems. There are few, if any, effective strategies to enhance security after [pic]design. One technique enforces the principle of least privilege to great extent, where an entity has only the privileges that are needed for its function. That way even if an attacker gains access to one part of the system, fine-grained security ensures that it is just as difficult for them to access the rest. Furthermore, by breaking the system up into smaller components, the complexity of individual components is reduced, opening up the possibility of using [pic]techniques such as automated theorem proving to prove the correctness of crucial software subsystems. This enables a closed form solution to security that works well when only a single well-characterized property can be isolated as critical, and that property is also assessable to math. Not surprisingly, it is impractical for generalized correctness, which probably cannot even be defined, much less proven. Where formal correctness proofs are not possible, rigorous use of code review and unit testing represent a best-effort approach to make modules secure. The [pic]design should use "defense in depth", where more than one subsystem needs to be violated to compromise the integrity of the system and the information it holds. Defense in depth works when the breaching of one security measure does not provide a platform to facilitate subverting another. Also, the cascading principle acknowledges that several low hurdles does not make a high hurdle. So cascading several weak mechanisms does not provide the safety of a single stronger mechanism. Subsystems should default to secure settings, and wherever possible should be designed to "fail secure" rather than "fail insecure" (see fail safe for the equivalent in safety engineering). Ideally, a secure system should require a deliberate, conscious, knowledgeable and free decision on the part of legitimate authorities in order to make it insecure. In addition, security should not be an all or nothing issue. The designers and operators of systems should assume that security breaches are inevitable. Full audit trails should be kept of system activity, so that when a security breach occurs, the mechanism and extent of the breach can be determined. Storing audit trails remotely, where they can only be appended to, can keep intruders from covering their tracks. Finally, full disclosure helps to ensure that when bugs are found the "window of vulnerability" is kept as short as possible.

Early history of security by design

The early Multics operating system was notable for its early emphasis on computer security by design, and Multics was possibly the very first operating system to be designed as a secure system from the ground up. In spite of this, Multics' security was broken, not once, but repeatedly. The strategy was known as 'penetrate and test' and has become widely known as a non-terminating process that fails to produce computer security. This led to further work on computer security that prefigured modern security engineering techniques producing closed form processes that terminate.

Secure coding

If the operating environment is not based on a secure operating system capable of maintaining a domain for its own execution, and capable of protecting application code from malicious subversion, and capable of protecting the system from subverted code, then high degrees of security are understandably not possible. While such secure operating systems are possible and have been implemented, most commercial systems fall in a 'low security' category because they rely on features not supported by secure operating systems (like portability, et al.). In low security operating environments, applications must be relied on to participate in their own protection. There are 'best effort' secure coding practices that can be followed to make an application more resistant to malicious subversion. In commercial environments, the majority of software subversion vulnerabilities result from a few known kinds of coding defects. Common software defects include buffer overflows, format string vulnerabilities, integer overflow, and code/command injection. Some common languages such as C and C++ are vulnerable to all of these defects (see Seacord, "Secure Coding in C and C++"). Other languages, such as Java, are more resistant to some of these defects, but are still prone to code/command injection and other software defects which facilitate subversion. Recently another bad coding practise has come under scrutiny; dangling pointers. The first known exploit for this particular problem was presented in July 2007. Before this publication the problem was known but considered to be academic and not practically exploitable. [2] In summary, 'secure coding' can provide significant payback in low security operating environments, and therefore worth the effort. Still there is no known way to provide a reliable degree of subversion resistance with any degree or combination of 'secure coding.'

Terms

The following terms used in engineering secure systems are explained below.

Firewall Firewalls can either be hardware devices or software programs. They provide excellent protection from online intrusion.

Automated theorem proving and other verification tools can enable critical algorithms and code used in secure systems to be mathematically proven to meet their specifications.

Thus simple microkernels can be written so that we can be sure they don't contain any bugs: eg EROS and Coyotos.

A bigger OS, capable of providing a standard API like POSIX, can be built on a microkernel using small API servers running as normal programs. If one of these API servers has a bug, the kernel and the other servers are not affected: e.g. Hurd.

Cryptographic techniques can be used to defend data in transit between systems, reducing the probability that data exchanged between systems can be intercepted or modified.

Strong authentication techniques can be used to ensure that communication end-points are who they say they are.

Secure cryptoprocessors can be used to leverage physical security techniques into protecting the security of the computer system.

Chain of trust techniques can be used to attempt to ensure that all software loaded has been certified as authentic by the system's designers.

Mandatory access control can be used to ensure that privileged access is withdrawn when privileges are revoked. For example, deleting a user account should also stop any processes that are running with that user's privileges.

Capability and access control list techniques can be used to ensure privilege separation and mandatory access control. The next sections discuss their use.

Some of the following items may belong to the computer insecurity article:

Do not run an application with known security flaws. Either leave it turned off until it can be patched or otherwise fixed, or delete it and replace it with some other application. Publicly known flaws are the main entry used by worms to automatically break into a system and then spread to other systems connected to it. The security website Secunia provides a search tool for unpatched known flaws in popular products.

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Cryptographic techniques involve transforming information, scrambling it so it becomes unreadable during transmission. The intended recipient can unscramble the message, but eavesdroppers cannot.

Backups are a way of securing information; they are another copy of all the important computer files kept in another location. These files are kept on hard disks, CD-Rs, CD-RWs, and tapes. Suggested locations for backups are a fireproof, waterproof, and heat proof safe, or in a separate, offsite location than that in which the original files are contained. Some individuals and companies also keep their backups in safe deposit boxes inside bank vaults. There is also a fourth option, which involves using one of the file hosting services that backs up files over the Internet for both business and individuals.

Backups are also important for reasons other than security. Natural disasters, such as earthquakes, hurricanes, or tornadoes, may strike the building where the computer is located. The building can be on fire, or an explosion may occur. There needs to be a recent backup at an alternate secure location, in case of such kind of disaster. The backup needs to be moved between the geographic sites in a secure manner, so as to prevent it from being stolen.

Anti-virus software consists of computer programs that attempt to identify, thwart and eliminate computer viruses and other malicious software (malware).

Firewalls are systems which help protect computers and computer networks from attack and subsequent intrusion by restricting the network traffic which can pass through them, based on a set of system administrator defined rules.

Access authorization restricts access to a computer to group of users through the use of authentication systems. These systems can protect either the whole computer - such as through an interactive logon screen - or individual services, such as an FTP server. There are many methods for identifying and authenticating users, such as passwords, identification cards, and, more recently, smart cards and biometric systems.

Encryption is used to protect the message from the eyes of others. It can be done in several ways by switching the characters around, replacing characters with others, and even removing characters from the message. These have to be used in combination to make the encryption secure enough, that is to say, sufficiently difficult to crack. Public key encryption is a refined and practical way of doing encryption. It allows for example anyone to write a message for a list of recipients, and only those recipients will be able to read that message.

Intrusion-detection systems can scan a network for people that are on the network but who should not be there or are doing things that they should not be doing, for example trying a lot of passwords to gain access to the network.

Pinging The ping application can be used by potential hackers to find if an IP address is reachable. If a hacker finds a computer they can try a port scan to detect and attack services on that computer.

Social engineering awareness - Keeping employees aware of the dangers of social engineering and/or having a policy in place to prevent social engineering can reduce successful breaches of the network and servers.

Honey pots are computers that are either intentionally or unintentionally left vulnerable to attack by hackers. They can be used to catch hackers or fix vulnerabilities.

Capabilities vs. ACLs

Within computer systems, the two fundamental means of enforcing privilege separation are access control lists (ACLs) and capabilities. The semantics of ACLs have been proven to be insecure in many situations (e.g., Confused deputy problem). It has also been shown that ACL's promise of giving access to an object to only one person can never be guaranteed in practice. Both of these problems are resolved by capabilities. This does not mean practical flaws exist in all ACL-based systems — only that the designers of certain utilities must take responsibility to ensure that they do not introduce flaws. Unfortunately, for various historical reasons, capabilities have been mostly restricted to research operating systems and commercial OSs still use ACLs. Capabilities can, however, also be implemented at the language level, leading to a style of programming that is essentially a refinement of standard object-oriented design. An open source project in the area is the E language. First the Plessey System 250 and then Cambridge CAP computer demonstrated the use of capabilities, both in hardware and software, in the 1970s, so this technology is hardly new. A reason for the lack of adoption of capabilities may be that ACLs appeared to offer a 'quick fix' for security without pervasive redesign of the operating system and hardware. The most secure computers are those not connected to the Internet and shielded from any interference. In the real world, the most security comes from operating systems where security is not an add-on, such as OS/400 from IBM. This almost never shows up in lists of vulnerabilities for good reason. Years may elapse between one problem needing remediation and the next. A good example of a secure system is EROS. But see also the article on secure operating systems. TrustedBSD is an example of an open source project with a goal, among other things, of building capability functionality into the FreeBSD operating system. Much of the work is already done.

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