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Logical security refers to the process of using software-based techniques for authenticating a user's privileges on a specific computer network or system. The concept is a part of the more complete field of computer security, which involves both hardware and software methods for securing a terminal or network. When discussing logical security, one should consider the different techniques used, which include usernames and passwords, token security, and two-way authentication on a system.
Password authentication is perhaps the most common and familiar type of logical security. Anyone who has ever used an online banking site or even a social networking system will be familiar with this concept. When a network has been configured to utilize password authentication, users attempting to log in to a specific terminal on the network are first forced to prove their credentials by inputting a username and password. The primary advantage here is simplicity; users need nothing more than their memorized username and password information to access the system. One major disadvantage is that the computer has no way to check whether the individual using a specific username and password combination is the authorized user; unscrupulous users can therefore steal usernames and passwords to crack the system.
Token security is a logical security technique that involves the use of keycards or other physical devices to authenticate a user on the network. Once the user swipes his card in the system, he is granted access to the computer. Some popular types of token devices contain a constantly changing code which switches to a new value every minute or so, keeping the system secure against individuals attempting to duplicate the security cards. Again, as with password authentication, there is no real safeguard against individuals stealing another person's passcard to gain access to the system.
Two-way authentication involves a question and answer exchange between the user and the computer system. When the user attempt to log in to the system, the computer will send a question — known as a "challenge" — and the end-user must reply with the correct result to gain access to the system. The advantage to this type of logical security technique is that the system is not tied down to a specific username and password combination; there can be any number of challenges, preventing unauthorized users from easily gaining access to the system by simply stealing one specific username and password combination.