Internet Draft Identifying ESP-NULL Packets December 2008 Network Working Group Manav Bhatia Internet Draft Alcatel-Lucent Intended Status: Proposed Standard Expires: May 2009 Identifying ESP-NULL Packets draft-bhatia-ipsecme-esp-null-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 2009. Abstract Encapsulating Security Payload (ESP) [RFC4303] provides data integrity protection, confidentiality and data origin authentication for data transported in an IP packet. There are various applications and protocols that do not require confidentiality but only need data integrity assurance or data origin authentication. Since ESP support is mandatory for IPSec, such applications end up using ESP with NULL encryption. However, because of the way ESP is defined, it is impossible for firewalls and intermediate routers to differentiate between encrypted ESP and ESP NULL packets by simply examining them. This poses Bhatia Expires April 2009 [Page 1]
Internet Draft Identifying ESP-NULL Packets December 2008 problems for the firewalls since such packets cannot be filtered and identified. It poses a different set of problems for routers since such packets cannot be properly filtered, classified and prioritized. This document proposes an extension to ESP so that firewalls and routers can disambiguate between ESP encrypted and ESP NULL encrypted packets. 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 in [RFC2119]. 1. Introduction ESP-NULL is used when confidentiality is not required and only source authentication and data integrity assurance is desired. IPSec mandates the use of ESP while keeps support for Authentication Header (AH) [RFC4302] as optional. Thus, new protocols using IPSec for data integrity also mandate the use of ESP-NULL. It is also mandatory [RFC4835] for all ESP implementations to provide support for ESP NULL encryption. Because of these factors a lot of vendors do not implement AH and only support ESP-NULL for data integrity and source authentication. The traffic using ESP-NULL is thus only going to increase with time. Firewalls and intermediate routers in the network find it impossible to parse ESP packets since they have no idea whether the packet is encrypted or not. They cannot for this reason implement filters and access control lists (ACLs). ACLs are highly desirable and used extensively by service providers to block undesired traffic coming from other domains. This draft therefore proposes an extension to ESP with which identifying an ESP-NULL packet from an ESP encrypted packet becomes trivial. It is backward compatible, therefore devices that do not understand this extension would treat packets using this extension as normal ESP packets. The extension described in this draft is applicable for both the tunnel and the transport modes of ESP. 2. Explicitly Marking ESP NULL Packets ESP-NULL packets, for both implementations based on [RFC2410] and [RFC4543] MUST be sent with a well known, reserved SPI of 1. The Bhatia Expires April 2009 [Page 2]
Internet Draft Identifying ESP-NULL Packets December 2008 original SPI should be included as part of the payload. This is encoded in the first 4 octets of the payload section of the ESP header. An implementation MUST put the next-header and the ESP header th th length as the 4 and the 5 octets of the payload. Since the packet is not encrypted these fields would be sent in clear text and would be visible to all. An extended ESP packet using NULL encryption would thus look like this: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved Security Parameters Index (RSPI) = 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Original Security Parameters Index (SPI) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | next-header | eESP HDRLen | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Payload Data* (variable) | ~ ~ | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Padding (0-255 bytes) | +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Pad Length | Next Header | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Authentication Data (variable) | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 Reserved Security Parameters Index (RSPI): Well known value that should be given by IANA to indicate that it is an ESP-NULL packet. next-header: This is a one octet field that indicates the next protocol header. Explicitly mentioning this provides an easy access to a HW parser to extract the upper layer protocol. eESP HDRLen: This is a one octet field that gives the length of the extended ESP header + IV (if mandated by the authentication algorithm). It is an offset to the beginning of the payload data. Bhatia Expires April 2009 [Page 3]
Internet Draft Identifying ESP-NULL Packets December 2008 Intermediate nodes (routers, firewalls, etc) interested in inspecting the packets en route can look at the SPI value at the start of the ESP header. If there are unaware of this extension then this packet would appear like a normal ESP packet. However, compliant implementations will understand that this is an extended ESP packet and would have enough information to be able to deep inspect the ESP- NULL packet. The compliant end nodes (routers) can similarly parse the packet easily. If the SPI value is 1, then it can extract the original SPI from the payload and process the packet accordingly. 3. Authenticating the Packets All fields of the extended ESP header starting with the RSPI and ending with the Next Header in the ESP trailer are included in the ESP data integrity check. The authentication data field is used to hold the result of the data integrity check done on the ESP packet. The length of this field depends on the authentication algorithm employed by the Security Association (SA) used to process this packet. 4. Acknowledgements The author would like to thank Jack Kohn for his useful comments. 5. IANA Considerations IANA must assign a value that for Reserved SPI which will be used as described above. The draft uses a value 1 to foster pre-standard implementations. 6. Security Considerations This proposal neither increases nor decreases the security for ESP. All considerations valid for ESP also apply here. 7. References 7.1 Normative References [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, December 2005. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP 14, February 2001. Bhatia Expires April 2009 [Page 4]
Internet Draft Identifying ESP-NULL Packets December 2008 [RFC2410] Glenn, R., and Kent, S., "The NULL Encryption Algorithm and its Use With IPsec", RFC 2410, November 1998. [RFC4543] McGrew, D. and Viega, J., "The Use of Galois Message Authentication Code (GMAC) in IPsec ESP and AH", RFC 4543, May 2006. 7.2 Informative References [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December 2005. [RFC4835] Manral, V., "Cryptographic Algorithm Implementation Requirements for Encapsulating Security Payload (ESP) and Authentication Header (AH)", RFC 4835, APRIL 2007. 8. Author's Addresses Manav Bhatia Alcatel-Lucent, Bangalore, India Email: manav@alcatel-lucent.com Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights 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; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Bhatia Expires April 2009 [Page 5]
Internet Draft Identifying ESP-NULL Packets December 2008 Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Bhatia Expires April 2009 [Page 6]