Network Working Group Mike StJohns
Request for Comments: 931 TPSC
Supersedes: RFC 912 January 1985
STATUS OF THIS MEMO
This RFC suggests a proposed protocol for the ARPA-Internet
community, and requests discussion and suggestions for improvements.
This is the second draft of this proposal (superseding RFC 912) and
incorporates a more formal description of the syntax for the request
and response dialog, as well as a change to specify the type of user
identification returned. Distribution of this memo is unlimited.
The Authentication Server Protocol provides a means to determine the
identity of a user of a particular TCP connection. Given a TCP port
number pair, it returns a character string which identifies the owner
of that connection on the server's system. Suggested uses include
automatic identification and verification of a user during an FTP
session, additional verification of a TAC dial up user, and access
verification for a generalized network file server.
This is a connection based application on TCP. A server listens for
TCP connections on TCP port 113 (decimal). Once a connection is
established, the server reads one line of data which specifies the
connection of interest. If it exists, the system dependent user
identifier of the connection of interest is sent out the connection.
The service closes the connection after sending the user identifier.
Queries are permitted only for fully specified connections. The
local/foreign host pair used to fully specify the connection are
taken from the query connection. This means a user on Host A may
only query the server on Host B about connections between A and B.
RFC 931 January 1985
The server accepts simple text query requests of the form
where <local-port> is the TCP port (decimal) on the target (server)
system, and <foreign-port> is the TCP port (decimal) on the source
The response is of the form
<local-port>, <foreign-port> : <response-type> : <additional-info>
where <local-port>,<foreign-port> are the same pair as the query,
<response-type> is a keyword identifying the type of response, and
<additional info> is context dependent.
23, 6191 : USERID : MULTICS : StJohns.DODCSC.a
23, 6193 : USERID : TAC : MCSJ-MITMUL
23, 6195 : ERROR : NO-USER
A response can be one of two types:
In this case, <additional-info> is a string consisting of an
operating system name, followed by a ":", followed by user
identification string in a format peculiar to the operating system
indicated. Permitted operating system names are specified in
RFC-923, "Assigned Numbers" or its successors. The only other
names permitted are "TAC" to specify a BBN Terminal Access
Controller, and "OTHER" to specify any other operating system not
yet registered with the NIC.
RFC 931 January 1985
For some reason the owner of <TCP-port> could not be determined,
<additional-info> tells why. The following are suggested values
of <additional-info> and their meanings.
Either the local or foreign port was improperly specified.
The connection specified by the port pair is not currently in
Can't determine connection owner; reason unknown. Other values
may be specified as necessary.
Unfortunately, the trustworthiness of the various host systems that
might implement an authentication server will vary quite a bit. It
is up to the various applications that will use the server to
determine the amount of trust they will place in the returned
information. It may be appropriate in some cases restrict the use of
the server to within a locally controlled subnet.
1) Automatic user authentication for FTP
A user-FTP may send a USER command with no argument to the
server-FTP to request automatic authentication. The server-FTP
will reply with a 230 (user logged in) if it can use the
authentication. It will reply with a 530 (not logged in) if it
cannot authenticate the user. It will reply with a 500 or 501
(syntax or parameter problem) if it does not implement automatic
authentication. Please note that no change is needed to currently
implemented servers to handle the request for authentication; they
will reject it normally as a parameter problem. This is a
suggested implementation for experimental use only.
2) Verification for privileged network operations. For example,
having the server start or stop special purpose servers.
RFC 931 January 1985
3) Elimination of "double login" for TAC and other TELNET users.
This will be implemented as a TELNET option.
<request> ::= <port-pair> <CR> <LF>
<port-pair> ::= <integer-number> "," <integer-number>
<reply> ::= <reply-text> <CR> <LF>
<reply-text> ::= <error-reply> | <auth-reply>
<error-reply> ::= <port-pair> ":" ERROR ":" <error-type>
<auth-reply> ::= <port-pair> ":" USERID ":" <opsys> ":" <user-id>
<error-type> ::= INVALID-PORT | NO-USER | UNKNOWN-ERROR
<opsys> ::= TAC | OTHER | MULTICS | UNIX ...etc.
(See "Assigned Numbers")
Notes on Syntax:
1) White space (blanks and tab characters) between tokens is not
important and may be ignored.
2) White space, the token separator character (":"), and the port
pair separator character (",") must be quoted if used within a
token. The quote character is a back-slash, ASCII 92 (decimal)
("\"). For example, a quoted colon is "\:". The back-slash must
also be quoted if its needed to represent itself ("\\").
Notes on User Identification Format:
The user identifier returned by the server should be the standard one
for the system. For example, the standard Multics identifier
consists of a PERSONID followed by a ".", followed by a PROJECTID,
followed by a ".", followed by an INSTANCE TAG of one character. An
instance tag of "a" identifies an interactive user, and instance tag
of "m" identifies an absentee job (batch job) user, and an instance
tag of "z" identifies a daemon (background) user.
Each set of operating system users must come to a consensus as to
RFC 931 January 1985
what the OFFICIAL user identification for their systems will be.
Until they register this information, they must use the "OTHER" tag
to specify their user identification.
Notes on User Identification Translation:
Once you have a user identifier from a remote system, you must then
have a way of translating it into an identifier that meaningful on
the local system. The following is a sketchy outline of table driven
scheme for doing this.
The table consists of four columns, the first three are used to match
against, the fourth is the result.
USERID Opsys Address Result
MCSJ-MITMUL TAC 26.*.*.* StJohns
* MULTICS 192.5.42.* =
* OTHER 10.0.0.42 anonymous
MSJ ITS 10.3.0.44 StJohns
The above table is a sample one for a Multics system on MILNET at the
Pentagon. When an authentication is returned, the particular
application using the userid simply looks for the first match in the
table. Notice the second line. It says that any authentication
coming from a Multics system on Net 192.5.42 is accepted in the same
Obviously, various users will have to be registered to use this
facility, but the registration can be done at the same time the use
receives his login identity from the system.