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Key authentication is used to solve the problem of authenticating the keys of the person (say "person B") to whom some other person ("person A") is talking to or trying to talk to. In other words, it is the process of assuring that the key of "person A" held by "person B" does in fact belong to "person A" and vice versa. This is usually done after we assume that the keys have been shared among the two sides over some secure channel, although some of the algorithms share the keys at the time of authentication also. The simplest solution for this problem is for the two users concerned to meet face-to-face and exchange keys. However, for systems in which there are a large number of users or in which the users do not personally know each other (e.g., Internet shopping) this is not practical. There are various algorithm for both symmetric keys and asymmetric public key cryptography to solve this problem. ==Authentication using Shared Keys== For key authentication using the traditional symmetric key cryptography, this is the problem of assuring that there is no man-in-the-middle attacker who is trying to read or spoof the communication. There are various algorithms used now-a-days to prevent such attacks. The most common among the algorithms are Diffie–Hellman key exchange, authentication using Key distribution center, kerberos and Needham–Schroeder protocol. Other methods that can be used include Password-authenticated key agreement protocols etc.〔 http://www.amazon.com/Computer-Networks-Edition-Andrew-Tanenbaum/dp/0132126958〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Key authentication」の詳細全文を読む スポンサード リンク
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