Network Working Group K. Alagappan Request for Comments: 1412 Digital Equipment Corporation January 1993
Telnet Authentication: SPX
Status of this Memo
This memo defines an Experimental Protocol for the Internet community. Discussion and suggestions for improvement are requested. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited.
IAC SB AUTHENTICATION IS <authentication-type-pair> AUTH <SPX authentication token> IAC SE
This is used to pass the SPX authentication token to the remote side of the connection. (A document which describes the authentication token syntax is forthcoming.) The first octet of the <authentication-type-pair> value is SPX. The second octet is a modifier to the SPX authentication type.
IAC SB AUTHENTICATION REPLY <authentication-type-pair> ACCEPT <mutual response> IAC SE
This command indicates that the authentication was successful. After an SPX authentication exchange, both sides have securely established a random 8-byte key to be used as the default key for the ENCRYPTION option. If the AUTH_HOW_MUTUAL bit is set in the second octet of the authentication-type-pair, the sender includes the mutual response bytes. The receiver of the ACCEPT command compares the "mutual response" with its expected mutual response.
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RFC 1412 SPX for Telnet January 1993
(A document which describes the mutual response syntax is forth coming.) If the AUTH_HOW_ONE_WAY bit is set in the second octet of the authentication-type-pair, the sender includes zero bytes of mutual response.
IAC SB AUTHENTICATION REPLY <authentication-type-pair> REJECT <optional reason for rejection> IAC SE
This command indicates that the authentication was not successful, and if there is any more data in the sub-option, it is an ASCII text message of the reason for the rejection.
User "joe" may wish to log in as user "pete" on machine "foo". If "pete" has set things up on "foo" to allow "joe" access to his account, then the client would send IAC SB AUTHENTICATION NAME "pete" IAC SE IAC SB AUTHENTICATION IS SPX AUTH <joe's spx authentication token> IAC SE. The server would then authenticate the user as "joe" from the token information, and the server would send back either ACCEPT or REJECT. If mutual authentication is being used, the server would include in the ACCEPT message, a mutual response. The authorization check to see if "pete" is allowing "joe" to use his account is made after the authentication exchange is complete. Therefore, it is possible for the client to receive an ACCEPT response (based on the authentication token), but for joe to be denied access to log in to pete's account.
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RFC 1412 SPX for Telnet January 1993
Client Server IAC DO AUTHENTICATION IAC WILL AUTHENTICATION
[ The server is now free to request authentication information. ]
IAC SB AUTHENTICATION SEND SPX CLIENT|MUTUAL SPX CLIENT|ONE_WAY IAC SE
[ The server has requested mutual SPX authentication. If mutual authentication is not supported, then the server is willing to do one-way SPX authentication. ]
[ The client will now respond with the name of the user that it wants to log in as, and the SPX authentication token. ]
IAC SB AUTHENTICATION NAME "pete" IAC SE IAC SB AUTHENTICATION IS SPX CLIENT|MUTUAL AUTH <spx authentication token information> IAC SE
[ The server responds with an ACCEPT command to state that the authentication was successful. ]
[ If AUTH_HOW_MUTUAL, the server responds with the mutual response so the client can verify that it is really talking to the right server. ]
[ If AUTH_HOW_ONE_WAY, the server responds with a NULL mutual response, since the client is willing to trust the server already. ]
The ability to negotiate a common authentication mechanism between client and server is a feature of the authentication option that should be used with caution. When the negotiation is performed, no authentication has yet occurred. Therefore, each system has no way of knowing whether or not it is talking to the system it intends. An intruder could attempt to negotiate the use of an authentication system which is either weak, or already compromised by the intruder.
Kannan Alagappan Digital Equipment Corporation 550 King Street, LKG1-2/A19 Littleton, MA 01460
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