ActorsA	authentication serverC	clientD	client's domainS	serverC'	client's name in S's domain Message FragmentsChx	challenge sent by xKx	x's private keyKN	nonce keyERR	an error message K{Q} = Q encrypted with key K 	# C sends its challenge to S1) C->S	KC{Acchal, ChC, S}, C, D 	# S passes C's challenge to A, along with its own challenge2) S->A	KS{Aschal, ChS, C, D, KC{Acchal, ChC, S}}, S 	# A sends an encrypted challenge back to C relayed by S	# KN is a new key to be used in encrypting the conversation3) A->S->C	KC{KS{Astick, ChS, C', KN}, Actick, ChC, KN}, PADor3) A->S->C 	Aerr, ERR 	# C now trusts S to be S	# C sends the encrypted challenge back to S5) C->S	KS{Astick, ChS, C', KN} 	# S now trusts C to be C'6) S->C "OK" .TSK'x	x's auxiliary keyCnS	challenge for an aux key sent by S.TE From a non-plan 9 machineC->S	CS->C	CnSC->S	K'C{CnS}S->A	KS{Asnchal, ChS, C, CnS, K'C{CnS}}, SA->S	KS{Astick, ChS, C', KN}}S->C	ok The same protocol is used for file and compute server attaches.The last message is a ticket that a compute server acceptsto set the user name to C'. Changing passwordsA user can change her password by contacting the password serviceon the authentication server.  The protocol isA -> C	challengeC -> A	client KC{challenge, oldpassword, newpassword}A -> C	"password changed" or error messageold password and new password are 10 char wide fixed-width fields.challenge is an 64 bit random number