Authentication identifies who is requesting network services. The term authenticationusually refers to authenticating users but can also refer to authenticating devices or softwareprocesses. For example, some routing protocols support route authentication,whereby a router must pass some criteria before another router accepts its routing updates.Most security policies state that to access a network and its services, a user must enter alogin ID and password that are authenticated by a security server. To maximize security,one-time (dynamic) passwords can be used. With one-time password systems, a user’spassword always changes. This is often accomplished with a security card, also called aSmartcard. A security card is a physical device about the size of a credit card. The usertypes a personal identification number (PIN) into the card. The PIN is an initial level ofsecurity that simply gives the user permission to use the card. The card provides a onetimepassword that is used to access the corporate network for a limited time. The passwordis synchronized with a central security card server that resides on the network.Security cards are commonly used by telecommuters and mobile users. They are not usuallyused for LAN access.Authentication is traditionally based on one of three proofs:■ Something the user knows: This usually involves knowledge of a unique secret that isshared by the authenticating parties. To a user, this secret appears as a classic password,a PIN, or a private cryptographic key.■ Something the user has: This usually involves physical possession of an item that isunique to the user. Examples include password token cards, security cards, and hardwarekeys.■ Something the user is: This involves verification of a unique physical characteristic ofthe user, such as a fingerprint, retina pattern, voice, or face.Many systems use two-factor authentication, which requires a user to have two proofsof identity. An example is an access control system that requires a security card and apassword. With two-factor authentication, a compromise of one factor does not lead to acompromise of the system. An attacker could learn a password, but the password is uselesswithout the security card. Conversely, if the security card is stolen, it cannot be usedwithout the password.
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