(3rd-July-2021)
A distributed system is susceptible to a variety of threats mounted by intruders as well as legitimate users of the system. In an environment where a principal can impersonate another principal, principals must adopt a mutually suspicious attitude toward one another and authentication becomes an important requirement. Authentication is a process by which one principal verifies the identity of another principal. For example, in a client–server system, the server may need to authenticate the client. Likewise, the client may want to authenticate the server so that it is assured that it is talking to the right entity. Authentication is needed for both authorization and accounting functions. In one-way authentication, only one principal verifies the identity of the other principal, while in mutual authentication both communicating principals verify each other’s identity. A user gains access to a distributed system by logging on to a host in the system. In an open access environment where hosts are scattered across unrestricted areas, a host can be arbitrarily compromised, necessitating mutual authentication between the user and host. In a distributed system, authentication is carried out using a protocol involving message exchanges and these protocols are termed authentication protocols.
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