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.\" $Id: auth.nr,v 1.3 1992/06/26 22:59:17 stevea Exp stevea $
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.so rfc.macro
.ds TL Telnet Authentication Option
.ds SB Internet Engineering Task Force
.ds WG Telnet Working Group
.ds RN DRAFT
.ds ED D. Borman
.ds CE Cray Research, Inc.
.HD
Status of this Memo
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.nh
.ST
.\".hy
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.LT "1.  Command Names and Codes" 0.3i
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.LR 1.8i AUTHENTICATION 37
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.LR 1.8i IS 0
.LR 1.8i SEND 1
.LR 1.8i REPLY 2
.LR 1.8i NAME 3
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.LR 1.8i "Authentication Types" ""
.LR 1.8i NULL 0
.LR 1.8i KERBEROS_V4 1
.LR 1.8i KERBEROS_V5 2
.LR 1.8i SPX 3
.LR 1.8i RSA 6
.LR 1.8i LOKI 10
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.LR 1.8i "Modifiers" ""
.LR 2.2i AUTH_WHO_MASK 1
.LR 2.6i AUTH_CLIENT_TO_SERVER 0
.LR 2.6i AUTH_SERVER_TO_CLIENT 1
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.LR 2.2i AUTH_HOW_MASK 2
.LR 2.6i AUTH_HOW_ONE_WAY 0
.LR 2.6i AUTH_HOW_MUTUAL 2
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.LT "2.  Command Meanings" 0.3i
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This document makes reference to a "server" and a "client".
For the purposes of this document, the "server" is the side of
the connection that did the passive TCP open (TCP LISTEN state),
and the "client"
is the side of the connection that did the active open.
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IAC WILL AUTHENTICATION
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The client side of the connection sends this command to indicate
that it is willing to send and receive authentication information.
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IAC DO AUTHENTICATION
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The servers side of the connection sends this command to indicate
that it is willing to send and receive
authentication information.
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IAC WONT AUTHENTICATION
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The client side of the connection sends this command to indicate
that it refuses to send or receive authentication information;
the server side sends this command if it receives a DO AUTHENTICATION
command.
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IAC DONT AUTHENTICATION
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The server side of the connection sends this command to indicate
that it refuses to send or receive authentication information;
the client side sends this command if it receives a WILL AUTHENTICATION
command.
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IAC SB AUTHENTICATION SEND authentication-type-pair-list IAC SE
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The sender of this command (the server) requests that the remote side
send authentication information for one of the authentication
types listed in "authentication-type-pair-list".  The "authentication-type-pair-list"
is an ordered list of "authentication-type" pairs.
Only the server side (DO AUTHENTICATION) is allowed to send this.
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IAC SB AUTHENTICATION IS authentication-type-pair <auth data> IAC SE
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The sender of this command (the client) is sending the authentication
information for authentication type "authentication-type-pair".
Only the client side (WILL AUTHENTICATION) is allowed to send this.
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IAC SB AUTHENTICATION REPLY authentication-type-pair <auth data> IAC SE
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The sender of this command (the server) is sending a reply to the
the authentication information received in a previous
IS command.
Only the server side (DO AUTHENTICATION) is allowed to send this.
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IAC SB AUTHENTICATION NAME remote-user IAC SE
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This optional command is sent to specify the
account name on the remote host that the user wishes
to be authorized to use.
Note that authentication may succeed, and the authorization
to use a particular account may still fail.
Some authentication mechanisms may ignore this command.
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The "authentication-type-pair" is two octets, the first is the
authentication type, and the second is a modifier to the type.
There are currently two one bit fields defined in the modifier,
the AUTH_WHO_MASK bit and the AUTH_HOW_MASK bit, so there are
four possible combinations:
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AUTH_CLIENT_TO_SERVER
.br
AUTH_HOW_ONE_WAY
.br
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The client will send authentication information
about the local user to the server.
If the negotiation is successful, the
server will have authenticated the user
on the client side of the connection.
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AUTH_SERVER_TO_CLIENT
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AUTH_HOW_ONE_WAY
.br
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The server will authenticate itself to the client.
If the negotiation is successful, the
client will know that it is connected
to the server that it wants to be connected to.
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AUTH_CLIENT_TO_SERVER
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AUTH_HOW_MUTUAL
.br
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The client will send authentication information
about the local user to
the server, and then
the server will authenticate itself
to the client.
If the negotiation is successful, the
server will have authenticated the user
on the client side of the connection,
and the client will know that it is connected
to the server that it wants to be connected to.
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AUTH_SERVER_TO_CLIENT
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AUTH_HOW_MUTUAL
.br
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The server will authenticate itself
to the client, and then
the client will authenticate itself
to the server.
If the negotiation is successful, the
client will know that it is connected
to the server that it wants to be connected to,
and the server will know that the client
is who it claims to be.
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.LT "3.  Default Specification" 0.3i
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The default specification for this option is
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WONT AUTHENTICATION
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DONT AUTHENTICATION
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meaning there will not be any exchange of authentication
information.
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.LT "4.  Motivation" 0.3i
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One of the deficiences of the Telnet protocol is that
in order to log into remote systems, users have to
type their passwords, which are passed
in clear text through the network.
If the connections goes through untrusted networks,
there is the possibility that passwords will be
compromised by someone watching the packets as they go by.
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The purpose of the AUTHENTICATION option is to provide
a framework for the passing of authentication
information through the TELNET session.
This means that: 1) the users password will not be
sent in clear text across the network, and 2) if the
front end telnet process has the appropriate authentication
information, it can automatically send the information,
and the user will not have to type any password.
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It is intended that the AUTHENTICATION option be
general enough that it can be used to pass information
for any authentication system.
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.LT "5.  Security Implications" 0.3i
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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.
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.LT "6.  Implementation Rules" 0.3i
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WILL and DO are used only at the beginning of the connection
to obtain and grant permission for future negotiations.
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The authentication is only negotiated in one directions;
the server must send the "DO", and the client must
send the "WILL".
This restriction is due to the nature of authentication; there are three
possible cases; server authenticates client, client authenticates
server, and server and client authenticate each other.
By only negotiating the option in one direction, and then
determining which of the three cases is being used via
the suboption, potential ambiguity is removed.
If the server receives a "DO", it must respond with a "WONT".
If the client receives a "WILL", it must respond with a "DONT".
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Once the two hosts have exchanged a DO and a WILL, the server
is free to request authentication information.
In the request, a list of supported authentication
types is sent.
Only the server may send
requests ("IAC SB AUTHENTICATION SEND authentication-type-pair-list IAC SE").
Only
the client may transmit authentication information via the "IAC
SB AUTHENTICATION IS authentication-type ... IAC SE" command.
Only the server may send
replys ("IAC SB AUTHENTICATION REPLY authentication-type ... IAC SE").
As many IS and REPLY suboptions may be exchanged as are needed
for the particular authentication scheme chosen.
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If the client does not support any of the authentication types
listed in the authentication-type-pair-list,
a type of NULL should be used to indicate this in the IS reply.
Note that in this case, the server may choose to close the
connection.
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The order of the authentication types MUST be ordered to indicate a
preference for different authentication types, the first type being
the most preferred, and the last type the least preferred.
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The following is an example of use of the option:
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.EB
.ET Client Server
.ER
IAC DO AUTHENTICATION
.EL
IAC WILL AUTHENTICATION
.BC
The server is now free to request authentication information.
.EC
.ER
IAC SB AUTHENTICATION SEND
KERBEROS_V4 CLIENT|MUTUAL
KERBEROS_V4 CLIENT|ONE_WAY
IAC SE
.BC
The server has requested mutual Kerberos authentication,
but is willing to do just one-way Kerberos authentication.
The client will now respond with the name of the user
that it wants to log in as, and the
Kerberos ticket.
.EC
.EL
IAC SB AUTHENTICATION NAME "joe" IAC SE
.br
IAC SB AUTHENTICATION IS KERBEROS_V4 CLIENT|MUTUAL AUTH
4 7 1 67 82 65 89 46 67 7 9 77 0 48 24 49 244 109 240
50 208 43 35 25 116 104 44 167 21 201 224 229 145 20
2 244 213 220 33 134 148 4 251 249 233 229 152 77 2
109 130 231 33 146 190 248 1 9 31 95 94 15 120 224 0
225 76 205 70 136 245 190 199 147 155 13
IAC SE
.BC
The server responds with an ACCEPT command to state
that the authentication was successful.
.EC
.ER
IAC SB AUTHENTICATION REPLY KERBEROS_V4
CLIENT|MUTUAL ACCEPT IAC SE
.BC
Next, the client sends across a CHALLENGE to verify
that it is really talking to the right server.
.EC
.EL
IAC SB AUTHENTICATION IS KERBEROS_V4
CLIENT|MUTUAL CHALLENGE xx xx xx xx xx xx xx xx IAC SE
.BC
Lastly, the server sends across a RESPONSE to prove
that it really is the right server.
.ER
IAC SB AUTHENTICATION REPLY KERBEROS_V4
CLIENT|MUTUAL RESPONSE yy yy yy yy yy yy yy yy IAC SE
.EE
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It is expected that any implementation that supports the Telnet
AUTHENTICATION option will support all of this specification.
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.LT "7.  References" 0.3i
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.LT "[1]" 0.4i
Reynolds, Joyce, and Postel, Jon, "Assigned Numbers", RFC 1060,
ISI, March 1990
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.LT "Author's Address" 0.3i
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David A. Borman, Editor
.br
Cray Research, Inc.
.br
655F Lone Oak Drive
.br
Eagan, MN 55123
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Phone: (612) 452-6650
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Mailing List: telnet-ietf@CRAY.COM
.br
EMail: dab@CRAY.COM
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.LT "Chair's Address" 0.3i
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The working group can be contacted via the current chair:
.sp
Steve Alexander
.br
INTERACTIVE Systems Corporation
.br
1901 North Naper Boulevard
.br
Naperville, IL 60563-8895
.sp
Phone: (708) 505-9100 x256
.br
EMail: stevea@isc.com