RFC2485 - DHCP Option for The Open Groups User Authentication Protocol

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　　Network Working Group S. Drach
Request for Comments: 2485 Sun Microsystems
Category: Standards Track January 1999

DHCP Option for The Open Group's User Authentication Protocol

Status of this Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (1999). All Rights Reserved.

Abstract

This document defines a DHCP [1] option that contains a list of
pointers to User Authentication Protocol servers that provide user
authentication services for clients that conform to The Open Group
Network Computing Client Technical Standard [2].

Introduction

The Open Group Network Computing Client Technical Standard, a product
of The Open Group's Network Computing Working Group (NCWG), defines a
network computing client user authentication facility named the User
Authentication Protocol (UAP).

UAP provides two levels of authentication, basic and secure. Basic
authentication uses the Basic Authentication mechanism defined in the
HTTP 1.1 [3] specification. Secure authentication is simply basic
authentication encapsulated in an SSLv3 [4] session.

In both cases, a UAP client needs to obtain the IP address and port
of the UAP service. Additional path information may be required,
depending on the implementation of the service. A URL [5] is an
excellent mechanism for encapsulation of this information since many
UAP servers will be implemented as components within legacy HTTP/SSL
servers.

Most UAP clients have no local state and are configured when booted
through DHCP. No existing DHCP option [6] has a data field that
contains a URL. Option 72 contains a list of IP addresses for WWW
servers, but it is not adequate since a port and/or path can not be
specified. Hence there is a need for an option that contains a list
of URLs.

User Authentication Protocol Option

This option specifies a list of URLs, each pointing to a user
authentication service that is capable of processing authentication
requests encapsulated in the User Authentication Protocol (UAP). UAP
servers can accept either HTTP 1.1 or SSLv3 connections. If the list
includes a URL that does not contain a port component, the normal
default port is assumed (i.e., port 80 for http and port 443 for
https). If the list includes a URL that does not contain a path
component, the path /uap is assumed.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Length | URL list
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Code 98

Length The length of the data field (i.e., URL list) in
bytes.

URL list A list of one or more URLs separated by the ASCII
space character (0x20).

References

[1] Droms, R., "Dynamic Host Configuration Protocol", RFC2131,
March 1997.

[2] Technical Standard: Network Computing Client, The Open Group,
Document Number C801, October 1998.

[3] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., and T.
Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC
2068, January 1997.

[4] Freier, A., Karlton, P., and P. Kocher, "The SSL Protocol,
Version 3.0", Netscape Communications Corp., November 1996.
Standards Information Base, The Open Group,
http://www.db.opengroup.org/sib.htm#SSL_3.

[5] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
Resource Locators (URL)", RFC1738, December 1994.

[6] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC2132, March 1997.

Security Considerations

DHCP currently provides no authentication or security mechanisms.
Potential exposures to attack are discussed in section 7 of the DHCP
protocol specification.

The User Authentication Protocol does not have a means to detect
whether or not the client is communicating with a rogue
authentication service that the client contacted because it received
a forged or otherwise compromised UAP option from a DHCP service
whose security was compromised. Even secure authentication does not
provide relief from this type of attack. This security exposure is
mitigated by the environmental assumptions documented in the Network
Computing Client Technical Standard.

Author's Address

Steve Drach
Sun Microsystems, Inc.
901 San Antonio Road
Palo Alto, CA 94303

Phone: (650) 960-1300
EMail: drach@sun.com

Full Copyright Statement

Copyright (C) The Internet Society (1999). All Rights Reserved.

This document and translations of it may be copied and furnished to
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or assist in its implementation may be prepared, copied, published
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kind, provided that the above copyright notice and this paragraph are
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