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Linux Tutorial - Security - What You Can Do About It - System Security
  Changing Attitudes ---- Security and the Law  

System Security

In early versions of UNIX, account passwords and file permissions were the only types of security implemented. As computers became more widespread and those who wanted to gain unauthorized access became more devious, it became apparent that this was not enough. Since the US government was steadily increasing the number of agencies that had computers, the level of system security needed to be increased as well.

In 1985, the National Security Agency's National Computer Security Center (NCSC) created a set of computer security standards for the Defense Department, titled "Trusted Computer Systems Evaluation Criteria". This is commonly known as the "Orange Book" as it was published with an orange cover. (This is part of a series of documents by the DOD related to computer security, all with different colored covers.)

Within the Orange Book, there are four broad classes of security levels for computers:

DMinimal security
CDiscretionary protection
BMandatory protection
AVerified protection

The C class contains to sub-levels, C1 and C2, with C2 offering slightly more security than C1. Class B offers three sub-levels: B1, B2 and B3.

Traditional PC based operating systems, like DOS and Windows fall within class D. This minimal protection does not mean there is no security, just that it is not as high as the C class. You can buy add-on products to add passwords to your system or change the file attributes to prevent accidental erasure. There are even product available that will allow you to add passwords to DOS and Windows systems, but that's about it.

Class C systems include the features and functions to employ discretionary protection . That means that it is up to the system administrator's discretion to decide how much access people have. Class C1 systems offers enough security to let users keep their data private from other users and prevent it from being accidentally read or destroyed. As we've already talked about, standard UNIX already provides this level of security in the form of user passwords and file permissions. Class C2 demands tighter login procedures, auditing of security related events, and isolation of system resources.

B-Class systems implement mandatory protection. That is, the system administrator cannot turn it off if he or she likes. Class B1 systems have labeled protection. This means that security procedures and sensitivity labels are required for each file. (A sensitivity level is basically a security classification) Class B2 adds the requirement that the system must be able to account for every code in the system. This helps to prevent security holes such as Trojan horses. Class B3 deals with the security of data access, in terms of prevent tampering and notification of security-relevant events.

The most secure class, Class A1, requires verified designs. Although they are functionally the same as B3 systems, A1 systems have also been formally defined, as well as proven by tests.

For years, the orange book was seen as the bible for computer security. Often people would see a system that followed the guidelines specific ed for a C2 level of trust and call the machine C2 "secure." This is a misnomer. The machine is trusted to provide a certain level of security, but it is not "secure"

Recently, groups in several countries have gotten together to update the guidelines defined by the orange book. They have developed the "Common Criteria," which is a standard for security criteria. These countries are Canada, France, Great Britain, the Netherlands, Germany and the US. Acceptance by these countries has made this, more or less, the de facto standard for information technology security worldwide.

Two of the more important basis documents for the Common Criteria (CC) is the orange book and the Information Technology Security Evaluation Criteria from the Commission of the European Community (ITSEC). However, the CC is not just a synopsis of other documents, but rather it's planned that the CC will replace these other documents.

Two of the key concepts in the CC are the protection profile and the security target. The protection profile is not product specific, but after being reviewed, it becomes part of the CC. It documents a particular IT-security problem and the appropriate solution. For these the requirements for specific product types can be developed.

Security targets allow protection profiles to be fit to a specific product. In other words, the product as a particular goal, in regards to security. With this, the security target forms the basis of the evaluation. A product evaluation determines whether a particular product has properly identified and addressed a particular IT-security problem.

The CC will be expanded as needed. The version planned as of this writing will contain requirements for cryptology. Cryptology solves problems of confidentiality, data integrity, and verification. The first version already addresses the issues of data protection and secure communication, even over open networks.

The evaluation process has several stages. First, a product manufacturer identifies an IT-security problem and decides to develop a solution and wants to have it evaluated. If a protection profile exists for this problem, the manufacturer can fit the profile to the product through the security profile.

If there is no security profile, a new one can be developed and a standard established to measure similar products. However, a security target can be defined without reference to a protection profile.

First, the security target is evaluated according to the CC. Then the product itself is evaluated according to the security target. If the product passes the evaluation, it is given an Evaluation Assurance Level (EAL). The evaluation, which is conducted by an organization independent of the manufacturer confirms that there are no obvious security errors. In the case of a higher EAL, the evaluation confirms that there are no hidden errors. Also the evaluation confirms that there is user documentation.

One of the advantages that the CC brings is that it is flexible and provides a clear concept of security. Products that have been evaluated and certified by the CC will gain significance and acceptance. The costs resulting from the evaluation process will be compensated by the improvements to security as well as the increase in market demand for certified products. As of this writing, most of the protection profiles deal with network issues. However, because of it flexibility, the CC can be implemented is other areas.

For the current version of the CC, check out the web site of the Nation Institute of Standards and technology at: http://csrc.nist.gov/nistpubs/cc/.

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Copyright 2002-2009 by James Mohr. Licensed under modified GNU Free Documentation License (Portions of this material originally published by Prentice Hall, Pearson Education, Inc). See here for details. All rights reserved.
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