Overblog Suivre ce blog
Editer l'article Administration Créer mon blog
28 décembre 2010 2 28 /12 /décembre /2010 06:13

Computer security is a branch of computer technology known as information security as applied to computers and networks. The objective of computer security includes protection of information and property from theft, corruption, or natural disaster, while allowing the information and property to remain accessible and productive to its intended users (Dell XPS M1210 Batteryhttp://www.hdd-shop.co.uk .

The term computer system security means the collective processes and mechanisms by which sensitive and valuable information and services are protected from publication, tampering or collapse by unauthorized activities or untrustworthy individuals and unplanned events respectively (Dell Studio XPS 1340 Battery)    .

The strategies and methodologies of computer security often differ from most other computer technologies because of its somewhat elusive objective of preventing unwanted computer behavior instead of enabling wanted computer behavior  (Dell Studio XPS 1640 Battery)      .

Security by design

The technologies of computer security are based on logic. As security is not necessarily the primary goal of most computer applications, designing a program with security in mind often imposes restrictions on that program's behavior (Dell Vostro 1710 Battery)     .

There are 4 approaches to security in computing, sometimes a combination of approaches is valid:

  1. Trust all the software to abide by a security policy but the software is not trustworthy (this is computer insecurity) (Dell KM958 battery)    .
  2. Trust all the software to abide by a security policy and the software is validated as trustworthy (by tedious branch and path analysis for example).
  3. Trust no software but enforce a security policy with mechanisms that are not trustworthy (again this is computer insecurity) (Sony VGP-BPS13 battery)     .
  4. Trust no software but enforce a security policy with trustworthy hardware mechanisms.

Many systems have unintentionally resulted in the first possibility. Since approach two is expensive and non-deterministic, its use is very limited. Approaches one and three lead to failure  (Sony VGP-BPS13/B battery)   .

Because approach number four is often based on hardware mechanisms and avoids 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  (Sony VGP-BPS13/S battery)     .

There are various strategies and techniques used to design security systems. However there are few, if any, effective strategies to enhance security after 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  (Sony VGP-BPS13A/B battery)    .

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  (Sony VGP-BPS13B/B battery)      .

Furthermore, by breaking the system up into smaller components, the complexity of individual components is reduced, opening up the possibility of using techniques such as automated theorem proving to prove the correctness of crucial software subsystems  (Sony VGP-BPL9 battery)   .

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 assessible to math. Not surprisingly, it is impractical for generalized correctness, which probably cannot even be defined, much less proven  (Sony VGP-BPS13B/B battery)    .

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 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 (Sony VGP-BPL15 battery)   .

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  (Dell Inspiron E1505 battery)   .

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  (Dell Latitude E6400 battery)   .

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  (HP Pavilion dv6000 Battery)   .

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  (SONY VAIO VGN-FZ Battery) .

Security architecture

Security Architecture can be defined as the design artifacts that describe how the security controls (security countermeasures) are positioned, and how they relate to the overall information technology architecture  (SONY VAIO VGN-FZ18 Battery) .

These controls serve the purpose to maintain the system's quality attributes, among them confidentiality, integrity, availability, accountability and assurance." .

Hardware mechanisms that protect computers and data  (SONY VAIO VGN-FZ180E Battery)

Hardware based or assisted computer security offers grrtrnative to software-only computer security. Devices such as dongles may be considered more secure due to the physical access required in order to be compromised .

Secure operating systems

One use of the term computer security refers to technology to implement a secure operating system  (SONY VAIO VGN-FZ220E Battery) .

Much of this technology is based on science developed in the 1980s and used to produce, may be some of the most impenetrable operating systems ever. Though still valid, the technology is in limited use today, primarily because it imposes some changes to system management and also because it is not widely understood  (SONY VAIO VGN-FZ340E Battery)   .

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  (SONY VAIO VGN-FZ430E Battery)     .

The strategy is based on a coupling of special microprocessor hardware features, often involving thememory management unit, to a special correctly implemented 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 (SONY VAIO VGN-FZ460E Battery)   .

This capability is enabled because the configuration not only imposes a 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  (SONY VAIO VGN-FZ480E Battery)  .

Systems designed with such methodology represent the state of the art of computer security although products using such security are 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  (SONY VAIO VGN-FZ4000 Battery)     .

Secure operating systems designed this way are used primarily to protect national security information, military secrets, and the data of international financial institutions. 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  (SONY VAIO VGN-FZ31E Battery)    .)

The assurance of security depends not only on the soundness of the 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 functionality and assurance level (such as EAL levels) (SONY VAIO VGN-FZ31B Battery)   ,

and these are specified in aProtection Profile for requirements and a Security Target for product descriptions. None of these ultra-high assurance secure general purpose operating systems have been produced for decades or certified under the Common Criteria (SONY VAIO VGN-FZ31J Battery)     .

In USA parlance, the term High Assurance usually suggests the system has the right security functions that are implemented robustly enough to protect DoD and DoE classified information. Medium assurance suggests it can protect less valuable information, such as income tax information  (SONY VAIO VGN-FZ31M Battery)  .

Secure operating systems designed to meet medium robustness levels of security functionality and assurance have seen wider use within both government and commercial markets. Medium robust systems may provide the same security functions as high assurance secure operating systems but do so at a lower assurance level (such as Common Criteria levels EAL4 or EAL5) (SONY VAIO VGN-FZ31Z Battery)  .

Lower levels mean we can be less certain that the security functions are implemented flawlessly, and therefore less dependable. These systems are found in use on web servers, guards, database servers, and management hosts and are used not only to protect the data stored on these systems but also to provide a high level of protection for network connections and routing services (SONY VAIO VGN-FZ38M Battery)    .

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 SONY VGP-BPS8 Battery .

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 SONY VGP-BPS13 Battery .

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 injectionSONY VGP-BPS13/S Battery .

It is to be immediately noted that all of the foregoing are specific instances of a general class of attacks, where situations in which putative "data" actually contains implicit or explicit, executable instructions are cleverly exploited  SONY VGP-BPS13A/B Battery .

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  SONY VGP-BPS13B/B Battery .

Recently another bad coding practice 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  SONY VGP-BPS13A/S Battery .

Unfortunately, there is no theoretical model of "secure coding" practices, nor is one practically achievable, insofar as the variety of mechanisms are too wide and the manners in which they can be exploited are too variegated SONY VGP-BPS13AS Battery .

It is interesting to note, however, that such vulnerabilities often arise from archaic philosophies in which computers were assumed to be narrowly disseminated entities used by a chosen few, all of whom were likely highly educated, solidly trained academics with naught but the goodness of mankind in mind  (Dell Inspiron 1320n Battery)    .

Thus, it was considered quite harmless if, for (fictitious) example, a FORMAT string in a FORTRAN program could contain the J format specifier to mean "shut down system after printing." After all, who would use such a feature but a well-intentioned system programmer? It was simply beyond conception that software could be deployed in a destructive fashion  (Dell Inspiron 1464 Battery) .

It is worth noting that, in some languages, the distinction between code (ideally, read-only) and data (generally read/write) is blurred. In LISP, particularly, there is no distinction whatsoever between code and data, both taking the same form  (Dell Inspiron 1564 Battery)  :

an S-expression can be code, or data, or both, and the "user" of a LISP program who manages to insert an executable LAMBDA segment into putative "data" can achieve arbitrarily general and dangerous functionality. Even something as "modern" as Perl offers the eval() function, which enables one to generate Perl code and submit it to the interpreter, disguised as string data  (Dell Inspiron 1764 Battery)       .

Capabilities and access control lists

Within computer systems, two security models capable of enforcing privilege separation are access control lists (ACLs) and capability-based security. The semantics of ACLs have been proven to be insecure in many situations, e.g., the confused deputy problem  (Dell Studio 1450 Battery)    .

It has also been shown that the promise of ACLs 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, but only that the designers of certain utilities must take responsibility to ensure that they do not introduce flaws  (Dell Studio 1457 Battery)       .

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  (Dell Latitude D610 Battery)   .

First the Plessey System 250 and then Cambridge CAP computer demonstrated the use of capabilities, both in hardware and software, in the 1970s. 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  (Toshiba NB100 Battery)  .

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  (Toshiba Satellite M65 battery)   .


Computer security is critical in almost any technology-driven industry which operates on computer systems. Computer security can also be referred to as computer safety. The issues of computer based systems and addressing their countless vulnerabilities are an integral part of maintaining an operational industry  (Toshiba Satellite M60 battery) .

Cloud computing Security

Security in the cloud is challenging , due to varied degree of security features and management schemes within the cloud entitites. In this connection one logical protocol base need to evolve so that the entire gamet of components operate synchronously and securely (Dell Latitude D830 Battery) .

In aviation

The aviation industry is especially important when analyzing computer security because the involved risks include human life, expensive equipment, cargo, and transportation infrastructure  (Dell Latitude D620 Battery)   .

Security can be compromised by hardware and software malpractice, human error, and faulty operating environments. Threats that exploit computer vulnerabilities can stem from sabotage, espionage, industrial competition, terrorist attack, mechanical malfunction, and human error  (Dell Inspiron Mini 10 Battery)    .

The consequences of a successful deliberate or inadvertent misuse of a computer system in the aviation industry range from loss of confidentiality to loss of system integrity, which may lead to more serious concerns such as data theft or loss, network and air traffic control outages, which in turn can lead to airport closures, loss of aircraft, loss of passenger life  (Sony VGN-FW11S Battery) .

Military systems that control munitions can pose an even greater risk.

A proper attack does not need to be very high tech or well funded; for a power outage at an airport alone can cause repercussions worldwide   (Sony VGN-FW11M Battery)    .

One of the easiest and, arguably, the most difficult to trace security vulnerabilities is achievable by transmitting unauthorized communications over specific radio frequencies. These transmissions may spoof air traffic controllers or simply disrupt communications altogether  (Sony VGN-FW139E/H battery)   .

These incidents are very common, having altered flight courses of commercial aircraft and caused panic and confusion in the past. Controlling aircraft over oceans is especially dangerous because radar surveillance only extends 175 to 225 miles offshore. Beyond the radar's sight controllers must rely on periodic radio communications with a third party (Dell Latitude E5400 Battery) .

Lightning, power fluctuations, surges, brown-outs, blown fuses, and various other power outages instantly disable all computer systems, since they are dependent on an electrical source. Other accidental and intentional faults have caused significant disruption of safety critical systems throughout the last few decades and dependence on reliable communication and electrical power only jeopardizes computer safety  (Dell Latitude E4200 Battery)   .

Notable system accidents

In 1994, over a hundred intrusions were made by unidentified crackers into the Rome Laboratory, the US Air Force's main command and research facility. Using trojan horse viruses, hackers were able to obtain unrestricted access to Rome's networking systems and remove traces of their activities  (Dell Vostro A840 Battery)   .

The intruders were able to obtain classified files, such as air tasking order systems data and furthermore able to penetrate connected networks of National Aeronautics and Space Administration's Goddard Space Flight Center, Wright-Patterson Air Force Base, some Defense contractors, and other private sector organizations, by posing as a trusted Rome center user  (Dell Inspiron 300M Battery) .

Electromagnetic interference is another threat to computer safety and in 1989, a United States Air Force F-16 jet accidentally dropped a 230 kg bomb in West Georgia after unspecified interference caused the jet's computers to release it  (Dell Studio 1737 battery)   .

Computer security policy

United States

Cybersecurity Act of 2010

On April 1, 2009, Senator Jay Rockefeller (D-WV) introduced the "Cybersecurity Act of 2009 - S. 773" (full text) in the Senate  (Dell Inspiron E1505 battery) ;

the bill, co-written with Senators Evan Bayh (D-IN), Barbara Mikulski (D-MD), Bill Nelson (D-FL), and Olympia Snowe (R-ME), was referred to the Committee on Commerce, Science, and Transportation, which approved a revised version of the same bill (the "Cybersecurity Act of 2010") on March 24, 2010  (Dell RM791 battery)    .

The bill seeks to increase collaboration between the public and the private sector on cybersecurity issues, especially those private entities that own infrastructures that are critical to national security interests (the bill quotes John Brennan, the Assistant to the President for Homeland Security and Counterterrorism  (Dell XPS M1530 battery)     :

"our nation’s security and economic prosperity depend on the security, stability, and integrity of communications and information infrastructure that are largely privately-owned and globally-operated" and talks about the country's response to a "cyber-Katrina" .), increase public awareness on cybersecurity issues, and foster and fund cybersecurity research  (Dell XPS M2010 battery)     .

Some of the most controversial parts of the bill include Paragraph 315, which grants the President the right to "order the limitation or shutdown of Internet traffic to and from any compromised Federal Government or United States critical infrastructure information system or network  (Acer Aspire One battery)   .

" The Electronic Frontier Foundation, an international non-profit digital rights advocacy and legal organization based in the United States, characterized the bill as promoting a "potentially dangerous approach that favors the dramatic over the sober response" (Toshiba Satellite P10 Battery) .

International Cybercrime Reporting and Cooperation Act

On March 25, 2010, Representative Yvette Clarke (D-NY) introduced the "International Cybercrime Reporting and Cooperation Act - H.R.4962" (full text) in the House of Representatives; the bill, co-sponsored by seven other representatives (among whom only one Republican), was referred to three House committees  (SONY VGN-FZ210CE Battery)  .

The bill seeks to make sure that the administration keeps Congressinformed on information infrastructure, cybercrime, and end-user protection worldwide. It also "directs the President to give priority for assistance to improve legal, judicial, and enforcement capabilities with respect to cybercrime to countries with low information and communications technology levels of development or utilization in their critical infrastructure (Dell Precision M70 Battery) ,

telecommunications systems, and financial industries"  as well as to develop an action plan and an annual compliance assessment for countries of "cyber concern".

Protecting Cyberspace as a National Asset Act of 2010 ("Kill switch bill")

On June 19, 2010, United States Senator Joe Lieberman (I-CT) introduced a bill called "Protecting Cyberspace as a National Asset Act of 2010 - S.3480" (full text in pdf) (Toshiba Satellite L305 Battery)   ,

which he co-wrote with Senator Susan Collins (R-ME) and Senator Thomas Carper (D-DE). If signed into law, this controversial bill, which the American media dubbed the "Kill switch bill", would grant the President emergency powers over the Internet. However, all three co-authors of the bill issued a statement claiming that instead, the bill "  existing broad Presidential authority to take over telecommunications networks"  (Toshiba Satellite T4900 Battery)  .


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

  • Authentication techniques can be used to ensure that communication end-points are who they say they are  (Toshiba PA3399U-2BRS battery)    .
  • 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.
  • Capability and access control list techniques can be used to ensure privilege separation and mandatory access control. This section discusses their use  (Toshiba Satellite A200 Battery)     .
  • 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.
  • 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   (Toshiba Satellite 1200 Battery)        .
  • Firewalls can provide some protection from online intrusion.
  • A microkernel is a carefully crafted, deliberately small corpus of software that underlies the operating system per se and is used solely to provide very low-level, very precisely defined primitives upon which an operating system can be developed. A simple example with considerable didactic value is the early '90s GEMSOS (Gemini Computers) (Toshiba Satellite M300 Battery)  ,
  • which provided extremely low-level primitives, such as "segment" management, atop which an operating system could be built. The theory (in the case of "segments") was that—rather than have the operating system itself worry about mandatory access separation by means of military-style labeling  (Sony Vaio PCG-5G2L Battery)
  • —it is safer if a low-level, independently scrutinized module can be charged solely with the management of individually labeled segments, be they memory "segments" or file system "segments" or executable text "segments." If software below the visibility of the operating system is (as in this case) charged with labeling  Sony Vaio PCG-5G3L Battery,
  • there is no theoretically viable means for a clever hacker to subvert the labeling scheme, since the operating system per sedoes not provide mechanisms for interfering with labeling: the operating system is, essentially, a client (an "application," arguably) atop the microkernel and, as such, subject to its restrictions  Sony Vaio PCG-5J1L Battery .
  • Endpoint Security software helps networks to prevent data theft and virus infection through portable storage devices, such as USB drives.

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

  • Access authorization restricts access to a computer to group of users through the use of authentication systems Sony Vaio PCG-5K2L Battery .
  • 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  Sony Vaio PCG-5J2L Battery .
  • Anti-virus software consists of computer programs that attempt to identify, thwart and eliminate computer viruses and other malicious software (malware) Sony Vaio PCG-5K1L Battery .
  • Applications with known security flaws should not be run. 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 Sony Vaio PCG-5L1L Battery .
  • The security website Secunia provides a search tool for unpatched known flaws in popular products.
  • 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  Sony Vaio PCG-6S2L Battery .
  • 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  Sony Vaio PCG-6S3L Battery .
  • 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  Sony Vaio PCG-6V1L Battery .
    • 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  Sony Vaio PCG-6W1L Battery .
    • There needs to be a recent backup at an alternate secure location, in case of such kind of disaster. Further, it is recommended that the alternate location be placed where the same disaster would not affect both locations Sony Vaio PCG-6W2L Battery .
    • Examples of alternate disaster recovery sites being compromised by the same disaster that affected the primary site include having had a primary site in World Trade Center I and the recovery site in 7 World Trade Center, both of which were destroyed in the 9/11 attack  Sony Vaio PCG-6W3L Battery ,
    • and having one's primary site and recovery site in the same coastal region, which leads to both being vulnerable to hurricane damage (e.g. primary site in New Orleans and recovery site in Jefferson Parish, both of which were hit by Hurricane Katrina in 2005)  Sony Vaio PCG-7111L Battery .
    • The backup media should be moved between the geographic sites in a secure manner, in order to prevent them from being stolen  Sony Vaio PCG-7112L Battery .

Cryptographic techniques involve transforming information, scrambling it so it becomes unreadable during transmission. The intended recipient can unscramble the message, but eavesdroppers cannot  Sony Vaio PCG-7113L Battery .

  • Encryption is used to protect the message from the eyes of others. Cryptographically secure ciphers are designed to make any practical attempt of breaking infeasible  Sony Vaio PCG-7133L Battery .
  • Symmetric-key ciphers are suitable for bulk encryption using shared keys, and public-key encryption usingdigital certificates can provide a practical solution for the problem of securely communicating when no key is shared in advance  Sony Vaio PCG-7Z1L Battery .
  • 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 Sony Vaio PCG-7Z2L Battery .
  • Honey pots are computers that are either intentionally or unintentionally left vulnerable to attack by crackers. They can be used to catch crackers or fix vulnerabilities  Sony Vaio PCG-8Y1L Battery .
  • 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  Sony Vaio PCG-8Y2L Battery .
  • Pinging The ping application can be used by potential crackers to find if an IP address is reachable. If a cracker finds a computer, they can try a port scan to detect and attack services on that computer  Sony Vaio PCG-8Z1L Battery .
  • Social engineering awareness keeps 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  Sony Vaio PCG-8Z2L Battery .
  • File Integrity Monitors are tools used to detect changes in the integrity of systems and files.

Computer insecurity

Many current computer systems have only limited security precautions in place. This computer insecurity article describes the current battlefield of computer security exploits and defenses  Sony VAIO PCG-5G2L Battery .

Please see the computer security article for an alternative approach, based on security engineering principles.

Security and systems design

Many current real-world computer security efforts focus on external threats, and generally treat the computer system itself as a trusted system  Sony VAIO PCG-5G3L Battery .

Some knowledgeable observers consider this to be a disastrous mistake, and point out that this distinction is the cause of much of the insecurity of current computer systems — once an attacker has subverted one part of a system without fine-grained security, he or she usually has access to most or all of the features of that system   Sony VAIO PCG-5J1L Battery .

Because computer systems can be very complex, and cannot be guaranteed to be free of defects, thissecurity stance tends to produce insecure systems.

Financial cost

Serious financial damage has been caused by computer security breaches, but reliably estimating costs is quite difficult Sony VAIO PCG-5K2L Battery .

Figures in the billions of dollars have been quoted in relation to the damage caused by malware such as computer worms like the Code Red worm, but such estimates may be exaggerated. However, other losses, such as those caused by the compromise of credit cardinformation  Sony VAIO PCG-5J2L Battery ,

can be more easily determined, and they have been substantial, as measured by millions of individual victims of identity theft each year in each of several nations, and the severe hardship imposed on each victim, that can wipe out all of their finances, prevent them from getting a job, plus be treated as if they were the criminal  Sony VAIO PCG-5K1L Battery .

Volumes of victims of phishing and other scams may not be known.

Individuals who have been infected with spyware or malware likely go through a costly and time-consuming process of having their computer cleaned  Sony VAIO PCG-5L1L Battery .

Spyware is considered to be a problem specific to the various Microsoft Windows operating systems , however this can be partially explained by the fact that Microsoft controls a major share of the PC market and thus represents the most prominent target  Sony VAIO PCG-6S2L Battery .


There are many similarities (yet many fundamental differences) between computer and physical security. Just like real-world security, the motivations for breaches of computer security vary between attackers, sometimes called hackers or crackers. Some are thrill-seekers or vandals (the kind often responsible for defacing web sites) Sony VAIO PCG-6S3L Battery ;

similarly, some web site defacements are done to make political statements. However, some attackers are highly skilled and motivated with the goal of compromising computers for financial gain or espionage. An example of the latter is Markus Hess (more diligent than skilled)  Sony VAIO PCG-6V1L Battery ,

who spied for the KGB and was ultimately caught because of the efforts of Clifford Stoll, who wrote a memoir, The Cuckoo's Egg, about his experiences  Sony VAIO PCG-6W1L Battery .

For those seeking to prevent security breaches, the first step is usually to attempt to identify what might motivate an attack on the system, how much the continued operation and information security of the system are worth, and who might be motivated to breach it  Sony VAIO PCG-6W2L Battery .

The precautions required for a home PC are very different for those of banks' Internet banking system, and different again for a classified military network. Other computer security writers suggest that, since an attacker using a network need know nothing about you or what you have on your computer, attacker motivation is inherently impossible to determine beyond guessing Sony VAIO PCG-6W3L Battery .

If true, blocking all possible attacks is the only plausible action to take.


To understand the techniques for securing a computer system, it is important to first understand the various types of "attacks" that can be made against it  Sony VAIO PCG-7111L Battery .

These threats can typically be classified into one of these seven categories:


An exploit (from the same word in the French language, meaning "achievement", or "accomplishment") is a piece of software, a chunk of data   Sony VAIO PCG-7112L Battery ,

or sequence of commands that take advantage of a software 'bug' or 'glitch' in order to cause unintended or unanticipated behavior to occur on computer software, hardware, or something electronic (usually computerized). This frequently includes such things as gaining control of a computer system or allowing privilege escalation or a denial of service attack  Sony VAIO PCG-7113L Battery .

Many development methodologies rely on testing to ensure the quality of any code released; this process often fails to discover unusual potential exploits. The term "exploit" generally refers to small programs designed to take advantage of a software flaw that has been discovered, either remote or local  Sony VAIO PCG-7133L Battery .

The code from the exploit program is frequently reused in trojan horses and computer viruses. In some cases, a vulnerability can lie in certain programs' processing of a specific file type, such as a non-executable media file. Some security web sites maintain lists of currently known unpatched vulnerabilities found in common programs (see "External links" below) Sony VAIO PCG-7Z1L Battery .


Eavesdropping is the act of surreptitiously listening to a private conversation, typically between hosts on a network. Even machines that operate as a closed system (i.e., with no contact to the outside world) can be eavesdropped upon via monitoring the faint electro-magnetic transmissions generated by the hardware such as TEMPEST  Sony VAIO PCG-7Z2L Battery .

The FBI's proposed Carnivore program was intended to act as a system of eavesdropping protocols built into the systems of internet service providers.

Social engineering and human error

A computer system is no more secure than the human systems responsible for its operation  Sony VAIO PCG-8Y1L Battery .

Malicious individuals have regularly penetrated well-designed, secure computer systems by taking advantage of the carelessness of trusted individuals, or by deliberately deceiving them, for example sending messages that they are the system administrator and asking for passwords  Sony VAIO PCG-8Y2L Battery .

This deception is known as Social engineering.

Denial-of-service attack

Unlike other exploits, denial of service attacks are not used to gain unauthorized access or control of a system. They are instead designed to render it unusable  Sony VAIO PCG-8Z1L Battery .

Attackers can deny service to individual victims, such as by deliberately entering a wrong password 3 consecutive times and thus causing the victim account to be locked, or they may overload the capabilities of a machine or network and block all users at onceSony VAIO PCG-8Z2L Battery .

These types of attack are, in practice, very hard to prevent, because the behavior of whole networks needs to be analyzed, not only the behaviour of small pieces of code.Distributed denial of service (DDoS) attacks are common, where a large number of compromised hosts (commonly referred to as "zombie computers", used as part of a botnet with, for example WD passport essential (500GB/640GB) ;

aworm, trojan horse, or backdoor exploit to control them.) are used to flood a target system with network requests, thus attempting to render it unusable through resource exhaustion. Another technique to exhaust victim resources is through the use of an attack amplifier   WD passport essential (250GB/320GB) —

where the attacker takes advantage of poorly designed protocols on 3rd party machines, such as FTP or DNS, in order to instruct these hosts to launch the flood. There are also commonly found vulnerabilities in applications that cannot be used to take control over a computer, but merely make the target application malfunction or crash  WD  passport essential SE (750GB/1TB)   .

This is known as a denial-of-service exploit.

Indirect attacks

An indirect attack is an attack launched by a third party computer  WD  passport elite(250GB/320GB) .

By using someone else's computer to launch an attack, it becomes far more difficult to track down the actual attacker. There have also been cases where attackers took advantage of public anonymizing systems, such as the tor onion router system WD passport elite(500GB/640GB) .


A backdoor in a computer system (or cryptosystem or algorithm) is a method of bypassing normal authentication, securing remote access to a computer, obtaining access to plaintext, and so on, while attempting to remain undetected  WD  passport studio for Mac(320GB/500GB) .

The backdoor may take the form of an installed program (e.g., Back Orifice), or could be a modification to an existing program or hardware device. A specific form of backdoors are rootkits, which replaces system binaries and/or hooks into the function calls of the operating system to hide the presence of other programs, users, services and open ports  WD  passport studio for Mac(500GB/640GB) .

It may also fake information about disk and memory usage.

Direct access attacks

Someone who has gained access to a computer can install any type of devices to compromise security, including operating system modifications, software worms, key loggers, and covert listening devices  WD  Elements series(250GB/320GB) .

The attacker can also easily download large quantities of data onto backup media, for instance CD-R/DVD-R, tape; or portable devices such as keydrives, digital cameras or digital audio players. Another common technique is to boot an operating system contained on a CD-ROM or other bootable media and read the data from the harddrive(s) this way  WD  Elements SE(500GB/640GB) .

The only way to defeat this is to encrypt the storage media and store the key separate from the system.

See also: Category:Cryptographic attacks

Reducing vulnerabilities

Computer code is regarded by some as a form of mathematics  WD Elements SE(750GB/1TB) .

It is theoretically possible to prove the correctness of certain classes of computer programs, though the feasibility of actually achieving this in large-scale practical systems is regarded as small by some with practical experience in the industry — seeBruce Schneier et al  WD  Elements desktop(500GB/640GB) .

It's also possible to protect messages in transit (i.e., communications) by means of cryptography. One method of encryption — the one-time pad — is unbreakable when correctly used. This method was used by the Soviet Union during the Cold War, though flaws in their implementation allowed some cryptanalysis (See Venona Project)  WD  Elements desktop(750GB/1TB) .

The method uses a matching pair of key-codes, securely distributed, which are used once-and-only-once to encode and decode a single message. For transmitted computer encryption this method is difficult to use properly (securely), and highly inconvenient as well  WD  Elements desktop(1.5 TB/2TB) .

Other methods of encryption, while breakable in theory, are often virtually impossible to directly break by any means publicly known today. Breaking them requires some non-cryptographic input, such as a stolen key, stolen plaintext (at either end of the transmission), or some other extra cryptanalytic information  WD  passport essential SE (750GB/1TB)--USB 3.0)   .

Social engineering and direct computer access (physical) attacks can only be prevented by non-computer means, which can be difficult to enforce, relative to the sensitivity of the information. Even in a highly disciplined environment, such as in military organizations, social engineering attacks can still be difficult to foresee and prevent  WD  passport essential (500GB/640GB) .

In practice, only a small fraction of computer program code is mathematically proven, or even goes through comprehensive information technology audits or inexpensive but extremely valuable computer security audits, so it's usually possible for a determined hacker to read  WD  passport for Mac(320GB/500GB) ,

copy, alter or destroy data in well secured computers, albeit at the cost of great time and resources. Few attackers would audit applications for vulnerabilities just to attack a single specific system. It is possible to reduce an attacker's chances by keeping systems up to date, using a security scanner or/and hiring competent people responsible for security  WD  passport for Mac(640GB/1TB) .

The effects of data loss/damage can be reduced by careful backing up and insurance.

Security measures

A state of computer "security" is the conceptual ideal, attained by the use of the three processes:

  1. Prevention  My book essential 4 generation  (640GB/1TB)
  2. Detection
  3. Response
  • User account access controls and cryptography can protect systems files and data, respectively  WD  My book essential 4 generation( 1.5TB/2TB) .
  • Firewalls are by far the most common prevention systems from a network security perspective as they can (if properly configured) shield access to internal network services, and block certain kinds of attacks through packet filtering  WD  My book elite( 1TB/1.5TB) .
  • Intrusion Detection Systems (IDS's) are designed to detect network attacks in progress and assist in post-attack forensics, while audit trails and logs serve a similar function for individual systems  WD  My book studio(1TB/2TB) .
  • "Response" is necessarily defined by the assessed security requirements of an individual system and may cover the range from simple upgrade of protections to notification of legal authorities, counter-attacks, and the like  WD  My book essential 4 generation( 1.5TB/2TB) .
  • In some special cases, a complete destruction of the compromised system is favored, as it may happen that not all the compromised resources are detected   WD  My book elite(640GB/2TB) .

Today, computer security comprises mainly "preventive" measures, like firewalls or an Exit Procedure. A firewall can be defined as a way of filtering network data between a host or a network and another network, such as the Internet, and can be implemented as software running on the machine  Seagate  expans

ion portable (320GB/500GB) ,

hooking into the network stack (or, in the case of most UNIX-based operating systems such asLinux, built into the operating system kernel) to provide realtime filtering and blocking. Another implementation is a so called physical firewall which consists of a separate machine filtering network traffic  Seagate  expansion (1.5TB/2TB) .

Firewalls are common amongst machines that are permanently connected to the Internet. However, relatively few organisations maintain computer systems with effective detection systems, and fewer still have organised response mechanisms in place  Seagate  Freeagent Desktop (500GB/1TB) .

Difficulty with response

Responding forcefully to attempted security breaches (in the manner that one would for attempted physical security breaches) is often very difficult for a variety of reasons  Seagate  Freeagent Go(250GB/320GB) :

  • Identifying attackers is difficult, as they are often in a different jurisdiction to the systems they attempt to breach, and operate through proxies, temporary anonymous dial-up accounts, wireless connections, and other anonymising procedures which make backtracing difficult and are often located in yet another jurisdiction  Seagate  Freeagent Go(500GB/640GB) .
  • If they successfully breach security, they are often able to deletelogs to cover their tracks.
  • The sheer number of attempted attacks is so large that organisations cannot spend time pursuing each attacker (a typical home user with a permanent (e.g., cable modem) connection will be attacked at least several times per day, so more attractive targets could be presumed to see many more)  Seagate  Freeagent Go(750GB/1TB) .
  • Note however, that most of the sheer bulk of these attacks are made by automated vulnerability scanners and computer worms.
  • Law enforcement officers are often unfamiliar with information technology, and so lack the skills and interest in pursuing attackers  Seagate  Freeagent Goflex(250GB/320GB) .
  • There are also budgetary constraints. It has been argued that the high cost of technology, such as DNA testing, and improved forensics mean less money for other kinds of law enforcement, so the overall rate of criminals not getting dealt with goes up as the cost of the technology increases  Seagate Freeagent Goflex(500GB/640GB) .
  • In addition, the identification of attackers across a network may require logs from various points in the network and in many countries, the release of these records to law enforcement Seagate  Freeagent Goflex(750GB/1TB)
  • (with the exception of being voluntarily surrendered by a network administrator or a system administrator) requires a search warrant and, depending on the circumstances, the legal proceedings required can be drawn out to the point where the records are either regularly destroyed, or the information is no longer relevant Seagate  Freeagent Goflex Pro(500GB/750GB) Seagate  Freeagent Goflex desktop(1TB/2TB).

Partager cet article

Repost 0
Published by batterys - dans Laptop Battery
commenter cet article