Authentication and Authorization

Because authentication and authorization are critical parts of secure communications, they must be emphasized. Authentication establishes the identity of the sender and/or the receiver of information. Any integrity check or confidential information is often meaningless if the identity of the sending or receiving party is not properly established.

Authorization is usually tightly coupled to authentication in most network resource access requirements. Authorization establishes what you are allowed to do once you've identified yourself (it is also called access control, capabilities, and permissions). It can be argued that authorization does not always require a priori authentication, but in this book, authentication and authorization are tightly coupled; authorization usually follows any authentication procedure.

Issues related to authentication and authorization include the robustness of the methods used in verifying an entity's identity, the establishment of trusted domains to define authorization boundaries, and the requirement of uniqueness in namespace.

Methods of Authentication

All methods of authentication require you to specify who or what you are and to relay appropriate credentials to prove that you are who you say you are. These credentials generally take the form of something you know, something you have, or something you are. What you know may be a password. What you have could be a smart card. What you are pertains to the field of biometrics, in which sophisticated equipment is used to scan a person's fingerprint or eye or to recognize a person's voice to provide authentication.

Authentication technologies are discussed in detail in Chapter 2, "Security Technologies." Here, the important element is to recognize that different mechanisms provide authentication services with varying degrees of certainty. Choosing the proper authentication technology largely depends on the location of the entities being authenticated and the degree of trust placed in the particular facets of the network.

Trust Models

Trust is the firm belief or confidence in the honesty, integrity, reliability, justice, and so on of another person or thing. Authorization is what you are allowed to do once your identity is established. All secure systems must have a framework for an organizational policy for authorization---this framework is called a trust model.

If something is difficult to obtain in a dishonest manner or is difficult to forge, we have inherent trust in that system. An example is the title to a car: This document is used as proof of ownership of a car because it is difficult to forge. It is this proof that authorizes a person to resell his or her car with the relative certainty that the car is actually his or hers to sell.

In the network world, trust models can be very complex. Suppose that we have a large corporation with a number of different affiliated departments---the research department, the marketing department, and the payroll department. These individual departments could structure their networks autonomously but with a spirit of cooperation. Each department sets up a trusted intermediary, which is the entity that keeps all the authentication and authorization information for the employees in that department (see Figure 1-9).

Figure 1-9: Trusted Intermediaries for Individual Corporate Departments

When an executive member of the research department wants to access a document off one of the research servers, he or she is authenticated by the research department's authentication/authorization server. Now if that same executive wants to access salary information for his or her employees, there must be a mechanism for authenticated and authorized access to the payroll department. Instead of each department server having separate account information for every user (this arrangement could become an administrative nightmare with large numbers of users), it may be necessary to create groups with inherited trust. For example, you can create an executive group on the payroll server that permits any executive member of the company to access payroll information.

Delegation of trust refers to giving someone or something permission to act on your behalf. If the executive from the research department went on vacation and left someone else in charge, this individual could have permission to act on the executive's behalf to carry out a salary modification. When the executive returns, the authorization must be revoked because it was granted only on a temporary basis.

The difficulty in many trust models is deciding who to trust. Weighting risk factors (the amount of damage that can be done if trust is inappropriately placed) and having adequate mechanisms to deal with misplaced trust should be a part of every corporate security policy. Creating a security policy is discussed in more detail in Chapter 6, "Design and Implementation of the Corporation Security Policy."

Note It is important to recognize that trust does not mean implicit trust. You should have a trust model that works in high probability, but you must verify the trust relationships and put in place checks to verify that information has not been compromised. As Ronald Reagan once said, "Trust, but verify."

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