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Network Working Group                                           P. DuffyRequest for Comments: 3594                                 Cisco SystemsCategory: Standards Track                                 September 2003PacketCable Security Ticket Control Sub-Optionfor the DHCP CableLabs Client Configuration (CCC) OptionStatus 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 (2003).  All Rights Reserved.Abstract   This document defines a new sub-option for the DHCP CableLabs Client   Configuration (CCC) Option.  This new sub-option will be used to   direct CableLabs Client Devices (CCDs) to invalidate security tickets   stored in CCD non volatile memory (i.e., locally persisted security   tickets).1.   Conventions used in this document   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inBCP 14,RFC 2119 [2].2.   Terminology   Definitions of terms/acronyms used throughout this document:   CCC - CableLabs Client Configuration option, described in [1].   CCD - CableLabs Client Device.  A PacketCable MTA is an example of a         CCD.   STC - Security Ticket Control.  The CCC sub-option described in this         document.Duffy                       Standards Track                     [Page 1]

RFC 3594                Security Ticket Control           September 2003   MTA - Media Terminal Adapter.  The CCD specific to the PacketCable         architecture.   PacketCable - multimedia architecture developed by CableLabs.  See         [8] for full details.3.   Introduction   The CableLabs Client Configuration Option [1] defines several   sub-options used to configure devices deployed into CableLabs   architectures.  These architectures implement the PacketCable   Security Specification [4] (based on Kerberos V5 [5]), to support CCD   authentication and establishment of security associations between   CCDs and application servers.   CCDs are permitted to retain security tickets in local persistent   storage.  Thus a power-cycled CCD is enabled to avoid expensive   ticket acquisition for locally persisted, non-expired tickets.  This   feature greatly reduces the security overhead of a deployment.   This sub-option allows the service provider to control the lifetime   of tickets persisted locally on a CCD.  The service provider requires   this capability to support operational functions such as forcing re-   establishment of security associations, remote testing, and remote   diagnostic of CCDs.   It should be noted that, although based on the Kerberos V5 RFC [5],   the PacketCable Security Specification is not a strict implementation   of this RFC.  See [4] for details of the PacketCable Security   Specification.4.   Security Ticket Control Sub-option   This sub-option defines a Ticket Control Mask (TCM) that instructs   the CCD to validate/invalidate specific application server tickets.   The sub-option is encoded as follows:    Code   Len      TCM   +-----+-----+-----+-----+   |  9  |  2  | m1  | m2  |   +-----+-----+-----+-----+   The length MUST be 2.  The TCM field is encoded as an unsigned 16 bit   quantity per network byte order.  Each bit of the TCM is assigned to   a specific server or server group.  A bit value of 0 means the CCD   MUST apply normal invalidation rules (defined in [4]) to the locallyDuffy                       Standards Track                     [Page 2]

RFC 3594                Security Ticket Control           September 2003   persisted ticket for the server/server group. A bit value of 1 means   the CCD MUST immediately invalidate the locally persisted ticket for   the server/server group.   Bit #0 is the least significant bit of the field.  The bit positions   are assigned as follows:      Bit #0 - the PacketCable Provisioning Server used by the CCD.      Bit #1 - the group of all PacketCable Call Management Servers used      by the CCD.      Bit #2 - #15.  Reserved and MUST be set to 0.   If a CCD does not locally store tickets, it MUST ignore this   sub-option.  Bit values not known to the CCD MUST be ignored.5.   IANA Considerations   IANA has assigned a sub-option code to this sub-option from the   "CableLabs Client Configuration" sub-option number space (maintained   within the BOOTP-DHCP Parameters Registry).   IANA has also set-up a new registry and will 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 insection 4 of this document.   IANA will register future bit mask definitions via an "IETF   Consensus" approval policy as described inRFC 2434 [3].6.   Security Considerations   Potential DHCP protocol attack exposure is discussed insection 7 of   the DHCP protocol specification [6] and in Authentication for DHCP   Messages [7].  Additional CCC attack exposure is discussed in [1].   The STC sub-option could be used to disrupt a CableLabs architecture   deployment.  In the specific case of PacketCable [8], a deployment   could be disrupted if a large number of MTAs are reset/power cycled,   initiate their provisioning flow [9], and are instructed by a   malicious DHCP server to invalidate all security tickets.  This could   lead to a Denial of Service (DoS) condition as this large set of MTAs   simultaneously attempt to authenticate and obtain tickets from the   security infrastructure.   However, the scenario described above is unlikely to occur. Within   the cable delivery architecture required by the various CableLabs   projects, the DHCP client is connected to a network through a cableDuffy                       Standards Track                     [Page 3]

RFC 3594                Security Ticket Control           September 2003   modem and the CMTS (head-end router).  The CMTS is explicitly   configured with a set of valid DHCP server addresses to which DHCP   requests are forwarded.  Further, a correctly configured CMTS will   only allow DHCP downstream traffic from 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.   Intellectual Property Statement   The IETF takes no position regarding the validity or scope of any   intellectual property or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; neither does it represent that it   has made any effort to identify any such rights.  Information on the   IETF's procedures with respect to rights in standards-track and   standards-related documentation can be found inBCP-11.  Copies of   claims of rights made available for publication and any assurances of   licenses to be made available, or the result of an attempt made to   obtain a general license or permission for the use of such   proprietary rights by implementors or users of this specification can   be obtained from the IETF Secretariat.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights which may cover technology that may be required to practice   this standard.  Please address the information to the IETF Executive   Director.Duffy                       Standards Track                     [Page 4]

RFC 3594                Security Ticket Control           September 20038.   References8.1.  Normative   [1] Beser, B. and P. Duffy, "DHCP Option for CableLabs Client       Configuration",RFC 3495, March 2003.   [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement       Levels",BCP 14,RFC 2119, March 1997.   [3] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA       Considerations Section in RFCs",RFC 2434, October 1998.   [4] "PacketCable Security Specification", PKT-SP-SEC-I09-030728,http://www.packetcable.com/downloads/specs/PKT-SP-SEC-I09-030728.pdf8.2.  Informative   [5] Kohl, J. and C. Neuman, "The Kerberos Network Authentication       Service (V5)",RFC 1510, September 1993.   [6] Droms, R., "Dynamic Host Configuration Protocol",RFC 2131, March       1997.   [7] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages",RFC3118, June 2001   [8] "PacketCable 1.0 Architecture Framework Technical Report",       PKT-TR-ARCH-V01-991201,http://www.packetcable.com/downloads/specs/pkt-tr-arch-v01-991201.pdf   [9] "PacketCable MTA Device Provisioning Specification",       PKT-SP-PROV-I07-030728,http://www.packetcable.com/downloads/specs/PKT-SP-PROV-I07-030728.pdfDuffy                       Standards Track                     [Page 5]

RFC 3594                Security Ticket Control           September 20039.   Acknowledgments   The author would like to acknowledge the effort of all those who   contributed to the development of the PacketCable Provisioning   specifications:   Sumanth Channabasappa (Alopa Networks); Angela Lyda, Rick Morris,   Rodney Osborne (Arris Interactive); Steven Bellovin and Chris   Melle (AT&T); Eugene Nechamkin (Broadcom); John Berg, Maria   Stachelek, Matt Osman, Venkatesh Sunkad (CableLabs); Klaus   Hermanns, Azita Kia, Michael Thomas, Paul Duffy (Cisco); Deepak   Patil (Com21); Jeff Ollis, Rick Vetter (General   Instrument/Motorola); Roger Loots, David Walters (Lucent); Peter   Bates (Telcordia); Patrick Meehan (Tellabs); Satish Kumar, Itay   Sherman, Roy Spitzer (Telogy/TI), Aviv Goren (Terayon);   Prithivraj Narayanan (Wipro), and Burcak Beser (Juniper   Networks).10.   Author's Address   Paul Duffy   Cisco Systems   1414 Massachusetts Avenue   Boxborough, MA 01719   EMail: paduffy@cisco.comDuffy                       Standards Track                     [Page 6]

RFC 3594                Security Ticket Control           September 200311.  Full Copyright Statement   Copyright (C) The Internet Society (2003).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assignees.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Duffy                       Standards Track                     [Page 7]