draft-ietf-dhc-pktc-kerb-tckt-01.txt   draft-ietf-dhc-pktc-kerb-tckt-02.txt 
Internet Engineering Task Force P. Duffy Internet Engineering Task Force P. Duffy
INTERNET DRAFT Cisco Systems INTERNET DRAFT Cisco Systems
DHC Working Group March 2003 DHC Working Group May 2003
Document: draft-ietf-dhc-pktc-kerb-tckt-01.txt Document: draft-ietf-dhc-pktc-kerb-tckt-02.txt
Security Ticket Control Sub-option PacketCable Security Ticket Control Sub-option
for the CableLabs Client Configuration Option. for the CableLabs Client Configuration Option.
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC 2026. with all provisions of Section 10 of RFC 2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
RFC 2119 [2]. RFC 2119 [2].
2. Terminology 2. Terminology
Definitions of terms/acronyms used throughout this document: Definitions of terms/acronyms used throughout this document:
CCC - CableLabs Client Configuration option, defined in [1]. CCC - CableLabs Client Configuration option, described in [1].
CCD - CableLabs Client Device. A PacketCable MTA is an example CCD - CableLabs Client Device. A PacketCable MTA is an example
of a CCD. of a CCD.
STC - Security Ticket Control. The CCC sub-option described in STC - Security Ticket Control. The CCC sub-option described in
this document. this document.
MTA - Media Terminal Adapter. The CCD specific to the PacketCable MTA - Media Terminal Adapter. The CCD specific to the PacketCable
architecture. architecture.
PacketCable - multimedia architecture developed by CableLabs. See PacketCable - multimedia architecture developed by CableLabs. See
[7] for full details. [8] for full details.
Security Ticket - a data object used to support establishment of
authentication and privacy relationships. Defined in the
PacketCable Security Specification[3].
3. Introduction 3. Introduction
The CableLabs Client Configuration Option [1] defines several sub- The CableLabs Client Configuration Option [1] defines several sub-
options used to configure devices deployed within CableLabs options used to configure devices deployed into CableLabs
architectures. These architectures implement the PacketCable architectures. These architectures implement the PacketCable
Security Specification [3] (based on Kerberos V5 [4]) to support Security Specification [4] (based on Kerberos V5 [5]), to
CCD authentication and establishment of security associations support CCD authentication and establishment of security
between CCDs and application servers. associations between CCDs and application servers.
CCDs are permitted to retain security tickets in local persistent CCDs are permitted to retain security tickets in local
storage. Thus a power-cycled CCD is enabled to avoid expensive persistent storage. Thus a power-cycled CCD is enabled to avoid
ticket acquisition for locally persisted, non-expired tickets. expensive ticket acquisition for locally persisted, non-expired
This feature greatly reduces the security overhead of a tickets. This feature greatly reduces the security overhead of
deployment. a deployment.
This sub-option allows the service provider to control the This sub-option allows the service provider to control the
lifetime of tickets persisted locally on a CCD. The service lifetime of tickets persisted locally on a CCD. The service
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provider requires this capability to support operational provider requires this capability to support operational
functions such as forcing authentication, remote testing, and functions such as forcing re-establishment of security
remote diagnostics of CCDs. associations, remote testing, and remote diagnostic of CCDs.
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It should be noted that, although based on the Kerberos V5 RFC It should be noted that, although based on the Kerberos V5 RFC
[4], the PacketCable Security Specification is not a strict [5], the PacketCable Security Specification is not a strict
implementation of this RFC. See [3] for details of the implementation of this RFC. See [4] for details of the
PacketCable Security Specification. PacketCable Security Specification.
4. Security Ticket Control Sub-option 4. Security Ticket Control Sub-option
This sub-option defines a Ticket Control Mask (TCM) that This sub-option defines a Ticket Control Mask (TCM) that
instructs the CCD to validate/invalidate specific application instructs the CCD to validate/invalidate specific application
server tickets. The sub-option is encoded as follows: server tickets. The sub-option is encoded as follows:
Code Len TCM Code Len TCM
+-----+-----+-----+-----+ +-----+-----+-----+-----+
| TBD | 2 | m1 | m2 | | TBD | 2 | m1 | m2 |
+-----+-----+-----+-----+ +-----+-----+-----+-----+
The length MUST be 2. The TCM field is encoded as an unsigned 16 The length MUST be 2. The TCM field is encoded as an unsigned 16
bit quantity per network byte-ordering rules. Each bit of the TCM bit quantity per network byte order. Each bit of the TCM is
is assigned to a specific server or server group. A bit value of assigned to a specific server or server group. A bit value of 0
0 means the CCD MUST apply normal invalidation rules (defined in means the CCD MUST apply normal invalidation rules (defined in
[3]) to the locally persisted ticket for the server/server group. [4]) to the locally persisted ticket for the server/server group.
A bit value of 1 means the CCD MUST immediately invalidate the A bit value of 1 means the CCD MUST immediately invalidate the
locally persisted ticket for the server/server group. locally persisted ticket for the server/server group.
Bit #0 is the least significant bit of the field. The bit Bit #0 is the least significant bit of the field. The bit
positions are assigned as follows. positions are assigned as follows.
Bit #0 - the PacketCable Provisioning Server used by the CCD. Bit #0 - the PacketCable Provisioning Server used by the CCD.
Bit #1 - the group of all PacketCable Call Management Servers Bit #1 - the group of all PacketCable Call Management Servers
used by the CCD. used by the CCD.
Bit #2 - #15. Reserved and MUST be set to 0. Bit #2 - #15. Reserved and MUST be set to 0.
If a CCD does not locally persist tickets, it MUST ignore this If a CCD does not locally store tickets, it MUST ignore this sub-
sub-option. option.
5. IANA Considerations 5. IANA Considerations
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IANA is requested to assign a sub-option code to this sub-option IANA is requested to assign a sub-option code to this sub-option
from the "CableLabs Client Configuration" sub-option number space from the "CableLabs Client Configuration" sub-option number space
(maintained within the BOOTP-DHCP Parameters Registry). (maintained within the BOOTP-DHCP Parameters Registry).
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IANA is also requested to maintain a new number space of
"CableLabs Client Configuration Option Ticket Control Mask Bit
Definitions", located in the BOOTP-DHCP Parameters Registry. The
initial bit definitions are described in section 4 of this
document. IANA is requested to register future bit mask
definitions via an "IETF Consensus" approval policy as described
in RFC 2434 [3].
6. Security Considerations 6. Security Considerations
Potential DHCP protocol attack exposure is discussed in section 7 Potential DHCP protocol attack exposure is discussed in section 7
of the DHCP protocol specification [5] and in Authentication for of the DHCP protocol specification [6] and in Authentication for
DHCP Messages [6]. Additional CCC attack exposure is discussed DHCP Messages [7]. Additional CCC attack exposure is discussed
in [1]. in [1].
The STC sub-option could be used to disrupt a CableLabs The STC sub-option could be used to disrupt a CableLabs
architecture deployment. In the specific case of PacketCable architecture deployment. In the specific case of PacketCable
[7], a deployment could be disrupted if a large number of MTAs [8], a deployment could be disrupted if a large number of MTAs
are reset/power cycled, initiate their provisioning flow [8], and are reset/power cycled, initiate their provisioning flow [9], and
are instructed by a malicious DHCP server to invalidate all are instructed by a malicious DHCP server to invalidate all
security tickets. This could lead to a Denial of Service (DoS) security tickets. This could lead to a Denial of Service (DoS)
condition as this large set of MTAs simultaneously attempt to condition as this large set of MTAs simultaneously attempt to
authenticate and obtain tickets from the security infrastructure. authenticate and obtain tickets from the security infrastructure.
However, the scenario described above is unlikely to occur. However, the scenario described above is unlikely to occur.
Within the cable delivery architecture required by the various Within the cable delivery architecture required by the various
CableLabs projects, the DHCP client is connected to a network CableLabs projects, the DHCP client is connected to a network
through a cable modem and the CMTS (head-end). The CMTS is through a cable modem and the CMTS (head-end router). The CMTS is
explicitly configured with a set of DHCP servers to which DHCP explicitly configured with a set of valid DHCP server addresses
requests are forwarded. Further, a correctly configured CMTS to which DHCP requests are forwarded. Further, a correctly
will only allow downstream traffic from specific IP configured CMTS will only allow DHCP downstream traffic from
addresses/ranges. specific DHCP server addresses.
It should be noted that the downstream filtering of DHCP packets
will not prevent spoofed DHCP servers behind the CMTS, but the
network infrastructure behind the CMTS is assumed to be closely
controlled by the service provider.
7. References 7. References
7.1. Normative 7.1. Normative
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[1] B. Beser and P. Duffy, "DHCP Option for CableLabs Client [1] B. Beser and P. Duffy, "DHCP Option for CableLabs Client
Configuration", http://www.ietf.org/internet-drafts/draft-ietf- Configuration", RFC 3495, March 2003.
dhc-packetcable-06.txt, January 2003.
[2] S. Bradner, "Key words for use in RFCs to Indicate Requirement [2] S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[3] "PacketCable Security Specification", PKT-SP-SEC-I07-021127, [3] T. Narten and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 2434, October 1998.
[4] "PacketCable Security Specification", PKT-SP-SEC-I08-030415,
http://www.packetcable.com/specifications.html http://www.packetcable.com/specifications.html
7.2. Informational 7.2. Informational
Duffy Expires September 2003 4 [5] J. Kohl and C. Neuman, "The Kerberos Network Authentication
[4] J. Kohl and C. Neuman, "The Kerberos Network Authentication
Service (V5)", RFC 1510, September 1993. Service (V5)", RFC 1510, September 1993.
[5] R. Droms, "Dynamic Host Configuration Protocol", RFC 2131, [6] R. Droms, "Dynamic Host Configuration Protocol", RFC 2131,
March 1997. March 1997.
[6] R. Droms and W. Arbaugh, "Authentication for DHCP Messages", [7] R. Droms and W. Arbaugh, "Authentication for DHCP Messages",
RFC 3118, June 2001 RFC 3118, June 2001
[7] "PacketCable Architecture Framework Technical Report", PKT- [8] "PacketCable Architecture Framework Technical Report", PKT-
TR-ARCH-V01-991201, TR-ARCH-V01-991201,
http://www.packetcable.com/specifications.html http://www.packetcable.com/specifications.html
[8] "PacketCable MTA Device Provisioning Specification", PKT-SP- [9] "PacketCable MTA Device Provisioning Specification", PKT-SP-
PROV-I05-021127. http://www.packetcable.com/specifications.html PROV-I06-030415. http://www.packetcable.com/specifications.html
8. Acknowledgments 8. Acknowledgments
The author would like to acknowledge the effort of all those who The author would like to acknowledge the effort of all those who
contributed to the development of the PacketCable Provisioning contributed to the development of the PacketCable Provisioning
specifications: specifications:
Sumanth Channabasappa (Alopa Networks); Angela Lyda, Rick Morris, Sumanth Channabasappa (Alopa Networks); Angela Lyda, Rick Morris,
Rodney Osborne (Arris Interactive); Steven Bellovin and Chris Rodney Osborne (Arris Interactive); Steven Bellovin and Chris
Melle (AT&T); Eugene Nechamkin (Broadcom); John Berg, Maria Melle (AT&T); Eugene Nechamkin (Broadcom); John Berg, Maria
Stachelek, Matt Osman (CableLabs); Klaus Hermanns, Azita Kia, Stachelek, Matt Osman, Venkatesh Sunkad (CableLabs); Klaus
Michael Thomas, Paul Duffy (Cisco); Deepak Patil (Com21); Jeff Hermanns, Azita Kia, Michael Thomas, Paul Duffy (Cisco); Deepak
Ollis, Rick Vetter (General Instrument/Motorola); Roger Loots, Patil (Com21); Jeff Ollis, Rick Vetter (General
David Walters (Lucent); Peter Bates (Telcordia); Patrick Meehan Instrument/Motorola); Roger Loots, David Walters (Lucent); Peter
(Tellabs); Satish Kumar, Itay Sherman, Roy Spitzer (Telogy/TI),
Aviv Goren (Terayon); Prithivraj Narayanan (Wipro), Burcak Beser
(Juniper Networks), and Rich Woundy (Comcast).
The author would also like to extend a special "thank you" to Duffy Expires November 2003 5
Eugene Nechamkin (Broadcom), David Atwood (Motorola), and Eric Bates (Telcordia); Patrick Meehan (Tellabs); Satish Kumar, Itay
RosenFeld (CableLabs) for their thoughtful inputs. Sherman, Roy Spitzer (Telogy/TI), Aviv Goren (Terayon);
Prithivraj Narayanan (Wipro), and Burcak Beser (Juniper
Networks).
9. Author's Addresses 9. Author's Addresses
Paul Duffy Paul Duffy
Cisco Systems Cisco Systems
300 Apollo Drive 300 Apollo Drive
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Chelmsford, MA, 01824 Chelmsford, MA, 01824
Email: paduffy@cisco.com Email: paduffy@cisco.com
10. Full Copyright Statement 10. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished This document and translations of it may be copied and furnished
to others, and derivative works that comment on or otherwise to others, and derivative works that comment on or otherwise
explain it or assist in its implementation may be prepared, explain it or assist in its implementation may be prepared,
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This document and the information contained herein is provided on This document and the information contained herein is provided on
an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE
OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY
IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
PURPOSE. PURPOSE.
Acknowledgement Acknowledgement
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Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
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