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She is logging into the client Client. Client and Server 0Iocommunicate. The protocol as implemented by Sun Microsystems and other vendors uses Diffie-Hellman for the key @Zexchange, but this protocol would actually work with any symmetric key exchange protocol. qd`$Client sends Annas name to Server. 1up nServer sends the Servers public key, Annas public key, and Annas private key enciphered under the DES with @'her password as the key to the Client. v`UClient obtains Annas password and deciphers Annas private key using that password. !x oClient computes the conversation key (the protocols term for an interchange key) using Annas private key and @Servers public key. y`\Server computes the same conversation key using Servers private key and Annas public key. !z pClient generates a 56-bit random session key, appends a Validator in fixed form, enciphers the result using the @*conversation key, and sends it to Server. {`?Server uses its computed conversation key to decipher message. !| Server checks Validator for presence of specific information (bits in specific places,  etc. ) If the Validator is corqrect, Server believes Anna has correctly authenticated herself, and both parties use the session key for further smessages. If the Validator is incorrect, Server believes Anna has not correctly authenticated herself, and rejects @ the attempt. ` Kerberos ) wKerberos is an authentication protocol requiring one or more trusted authentication servers. The authentication server *50stores the users password. In what follows,  T n,x  is a ticket identifying the user  n  to the service  x ,  A n  is an authenticator 0C3identifying the user  n ,  K n,x  is a session key that  n  and  x  can use to communicate, and  K x  is a cryptographic key (password) that user or service  x  and the authentication server share. The ticket  T n,x  contains the session key  K n,x . The UU@notation { x } y  means the message  x  enciphered with cryptographic key  y  (using the DES).  n*` Logging in `{Client sends user name and request for a ticket to use the  ticket granting service  to the authentication server. **`Authentication server responds with {{ T user,tgs } K tgs , K user,tgs ,} K user .  1Client uses locally entered user password  K user  to decipher message and obtain { T user,tgs } K tgs  and  K user,tgs . If the UUmpassword is incorrect, none of the messages between the authentication server and the user will decipher cor.@,rectly, nullifying the use of any services.  -`!Obtaining a Ticket for a Service *`3Client sends message:  service ,{ T user,tgs } K tgs ,{ A user } K user,tgs  to the ticket granting service  tgs . 1ܪ~ 'The ticket granting service uses its key  K tgs  to obtain the ticket  T user,tgs and, from that, the session key  K user,tgs . It uses the session key to obtain the authenticator  A user . It then verifies that the ticket was issued to the entity named UU@in the authenticator. *U!`2The ticket granting service replies to the client with the message {{ T user,service } K service , K user,service } K user,tgs . 1 *s The client uses the session key  K user,tgs  to obtain the session key  K user,service  to use with the desired service, and @aan enciphered message { T user,service } K service  to send the service.  UU0`Using a Service  *?`Client sends message: { A user } K user,service ,{ T user,service } K service  to the server. 1 Mh .The service uses its key  K service  to obtain the ticket  T user,service   and, from that, the session key  K user,service . It uses the session key to obtain the authenticator  A user . It then verifies that the ticket was issued to the entity named in UU@the authenticator. Y*uU `The server obtains the timestamp  t  from  T user,service   and replies with { t  + 1} K user,service . 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