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Saturday, March 26, 2011

Computer Security 2


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. These controls serve the purpose to maintain the system's quality attributes, among them confidentialityintegrityavailabilityaccountability and assurance.".


Hardware mechanisms that protect computers and data

Hardware based or assisted computer security offers an alternative 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. 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 in limited use today, primarily because it imposes some changes to system management and also because it is 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 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 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[clarification needed] 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. 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.) 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), and these are specified in a Protection Profile for requirements and a Security Targetfor product descriptions. None of these ultra-high assurance secure general purpose operating systems have been produced for decades or certified under Common Criteria.
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. 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). 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.

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 overflowsformat string vulnerabilitiesinteger overflow, and code/command injection. 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.
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 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.[2]
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. 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. 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.
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: 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.


source : en.wikipedia.org


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