Network Working Group M. Gupta Internet Draft Nokia Document: draft-ietf-ospf-ospfv3-auth-05.txt N. Melam Expires: April 2005 Nokia October 2004 Authentication/Confidentiality for OSPFv3 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 RFC 3668. 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. Abstract This document describes means/mechanisms to provide authentication/confidentiality to OSPFv3 using an IPv6 AH/ESP Extension Header. Copyright Notice Copyright (C) The Internet Society. (2004) 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 RFC-2119 [N7]. M. Gupta/N. Melam Expires - Apr 2005 [Page 1]
Internet Draft Authentication/Confidentiality to OSPFv3 October 2004 Table of Contents 1. Introduction...................................................2 2. Transport Mode vs Tunnel Mode..................................2 3. Authentication.................................................3 4. Confidentiality................................................3 5. Distinguishing OSPFv3 from OSPFv2..............................4 6. IPsec Requirements.............................................4 7. Key Management.................................................4 8. SA Granularity and Selectors...................................6 9. Virtual Links..................................................7 10. Changing Keys.................................................8 11. IPsec rules...................................................8 12. Mandatory Encryption and Authentication Algorithms...........10 13. Replay Protection............................................10 Security Considerations..........................................10 Normative References.............................................11 Informative References...........................................11 Acknowledgments..................................................11 Authors' Addresses...............................................12 1. Introduction OSPF (Open Shortest Path First) Version 2 [N1] defines fields AuType and Authentication in its protocol header in order to provide security. In OSPF for IPv6 (OSPFv3) [N2], both of the authentication fields were removed from OSPF headers. OSPFv3 relies on the IPv6 Authentication Header (AH) and IPv6 Encapsulating Security Payload (ESP) to provide integrity, authentication and/or confidentiality. This document describes how IPv6 AH/ESP extension headers can be used to provide authentication/confidentiality to OSPFv3. It is assumed that the reader is familiar with OSPFv3 [N2], AH [N5], ESP [N4], the concept of security associations, tunnel and transport mode of IPsec and the key management options available for AH and ESP (manual keying [N3] and Internet Key Exchange (IKE)[I1]). 2. Transport Mode vs Tunnel Mode Transport mode Security Association (SA) is the security association between two hosts or routers/gateways when they are acting as hosts. SA must be tunnel mode if either end of the security association is a router/gateway. OSPFv3 packets are exchanged between the routers but M. Gupta/N. Melam Expires - April 2005 [Page 2]
Internet Draft Authentication/Confidentiality to OSPFv3 October 2004 as the packets are destined to the routers, the routers act like hosts in this case. So transport mode SA MUST be used in order to provide required security to OSPFv3. 3. Authentication Implementations conforming to this specification MUST support Authentication for OSPFv3. In order to provide authentication to OSPFv3, "ESP with NULL encryption" MUST be supported and AH SHOULD be supported by the implementation. If "ESP with NULL encryption" in transport mode is used, it will provide authentication to only OSPFv3 protocol headers but not to the IPv6 header, extension headers and options. If AH in transport mode is used, it will provide authentication to OSPFv3 protocol headers, selected portions of IPv6 header, selected portions of extension headers and selected options. When OSPFv3 authentication is enabled, O OSPFv3 packets that are not protected with AH or ESP MUST be silently discarded. O OSPFv3 packets that fail the authentication checks MUST be silently discarded. 4. Confidentiality Implementations conforming to this specification SHOULD support confidentiality for OSPFv3. If confidentiality is provided, "ESP with non-null encryption" MUST be used. When OSPFv3 confidentiality is enabled, O OSPFv3 packets that are not protected with ESP MUST be silently discarded. O OSPFv3 packets that fail the confidentiality checks MUST be silently discarded. M. Gupta/N. Melam Expires - April 2005 [Page 3]
Internet Draft Authentication/Confidentiality to OSPFv3 October 2004 5. Distinguishing OSPFv3 from OSPFv2 The IP/IPv6 Protocol Type for OSPFv2 and OSPFv3 is same (89) and OSPF distinguishes them based on the OSPF header version number. However current IPsec standards do not allow using arbitrary protocol specific header fields as the selectors. Therefore, in order to distinguish OSPFv3 packets from the OSPFv2 packets, OSPF version field in the OSPF header cannot be used. As OSPFv2 is only for IPv4 and OSPFv3 is only for IPv6, version field in IP header can be used to distinguish OSPFv3 packets from OSPFv2 packets. 6. IPsec Requirements In order to implement this specification, the following IPsec capabilities are required. Transport Mode IPsec in transport mode MUST be supported. [N3] Traffic Selectors The implementation MUST be able to use interface index, source address, destination address, protocol and direction for choosing the right security action. Manual key support Manually configured keys MUST be able to secure the specified traffic. [N3] Encryption and Authentication Algorithms AES-CBC and HMAC-SHA1 MUST be supported as the encryption and the authentication algorithms respectively. [N6] Dynamic IPsec rule configuration Routing module SHOULD be able to configure, modify and delete IPsec rules on the fly. This is needed mainly for securing virtual links. 7. Key Management OSPFv3 exchanges both multicast and unicast packets. While running OSPFv3 over a broadcast interface, the authentication/confidentiality required is "one to many". Since IKE is based on the Diffie-Hellman key agreement protocol and works only for two communicating parties, it is not possible to use IKE for providing the required "one to many" authentication/confidentiality. Manual keying MUST be used for this purpose. In manual keying SAs are statically installed on the M. Gupta/N. Melam Expires - April 2005 [Page 4]
Internet Draft Authentication/Confidentiality to OSPFv3 October 2004 routers and these static SAs are used to authenticate/encrypt the packets. The following discussion explains that it is not scalable and practically infeasible to use different security associations for inbound and outbound traffic in order to provide the required "one to many" security. Therefore, the implementations MUST use manually configured keys with same SA for inbound and outbound traffic (as shown in Figure 3). A | SAa ------------>| SAb <------------| | B | SAb ------------>| SAa <------------| Figure: 1 | C | SAa/SAb ------------>| SAa/SAb <------------| | Broadcast Network If we consider communication between A and B in Figure 1, everything seems to be fine. A uses security association SAa for outbound packets and B uses the same for inbound packets and vice versa. Now if we include C in the group and C sends a packet out using SAa then only A will be able to understand it or if C sends the packets out using SAb then only B will be able to understand it. Since the packets are multicast packets and they are going to be processed by both A and B, there is no SA for C to use so that A and B both can understand it. A | SAa ------------>| SAb <------------| SAc <------------| | B | SAb ------------>| SAa <------------| Figure: 2 SAc <------------| | M. Gupta/N. Melam Expires - April 2005 [Page 5]
Internet Draft Authentication/Confidentiality to OSPFv3 October 2004 C | SAc ------------>| SAa <------------| SAb <------------| | Broadcast Network The problem can be solved by configuring SAs for all the nodes on all the nodes as shown in Figure 2. So A, B and C will use SAa, SAb and SAc respectively for outbound traffic. Each node will lookup the SA to be used based on the source (A will use SAb and SAc for packets received from B and C respectively). This solution is not scalable and practically infeasible because every node will need to be configured with a large number of SAs and addition of a node in the network will cause addition of another SA on all the nodes. A | SAs ------------>| SAs <------------| | B | SAs ------------>| SAs <------------| Figure: 3 | C | SAs ------------>| SAs <------------| | Broadcast Network The problem can also be solved by using the same SA for inbound and outbound traffic as shown in Figure 3. 8. SA Granularity and Selectors The user SHOULD be given a choice to share the same SA among multiple interfaces or using unique SA per interface. OSPFv3 supports running multiple instances over one interface using the "Instance Id" field contained in the OSPFv3 header. As IPsec does not support arbitrary fields in protocol header to be used as the selectors, it is not possible to use different SAs for different instances of OSPFv3 running over the same interface. Therefore, all the instances of OSPFv3 running over the same interface will have to M. Gupta/N. Melam Expires - April 2005 [Page 6]
Internet Draft Authentication/Confidentiality to OSPFv3 October 2004 use the same SA. In OSPFv3 RFC terminology, SAs are per-link and not per-interface. 9. Virtual Links Different SA than the SA of underlying interface MUST be provided for virtual links. Packets sent out on virtual links use unicast non- link local IPv6 addresses as the IPv6 source address and all the other packets use multicast and unicast link local addresses. This difference in the IPv6 source address is used in order to differentiate the packets sent on interfaces and virtual links. As the end point IP addresses of the virtual links are not known at the time of configuration, the secure channel for these packets needs to be set up dynamically. The end point IP addresses of virtual links are learned during the routing table build up process. The packet exchange over the virtual links starts only after the discovery of end point IP addresses. In order to provide security to these exchanges, the routing module should setup a secure IPsec channel dynamically once it acquires the required information. According to the OSPFv3 RFC [N2], the virtual neighbor's IP address is set to the first prefix with the "LA-bit" set from the list of prefixes in intra-area-prefix-LSAs originated by the virtual neighbor. But when it comes to choosing the source address for the packets that are sent over the virtual link, the RFC simply suggests using one of the router's own site-local or global IPv6 addresses. In order to install the required security rules for virtual links, the source address also needs to be predictable. So the routers that implement this specification MUST change the way the source and destination addresses are chosen for the packets exchanged over virtual links when the security is enabled on that virtual link. The first IPv6 address with the "LA-bit" set in the list of prefixes advertised in intra-area-prefix-LSAs in the transit area MUST be used as the source address for packets exchanged over the virtual link. When multiple intra-area-prefix-LSAs are originated they are considered as being concatenated and are ordered by ascending Link State ID. The first IPv6 address with the "LA-bit" set in the list of prefixes received in intra-area-prefix-LSAs from the virtual neighbor in the transit area MUST be used as the destination address for packets exchanged over the virtual link. When multiple intra-area-prefix- LSAs are received they are considered as being concatenated and are ordered by ascending Link State ID. M. Gupta/N. Melam Expires - April 2005 [Page 7]
Internet Draft Authentication/Confidentiality to OSPFv3 October 2004 This makes both the source and destination addresses of the packets exchanged over the virtual link, predictable on both the routers for security purposes. 10. Changing Keys To maintain the security of a link, the key values SHOULD be changed from time to time. The following three-step procedure SHOULD be provided to rekey the routers on a link without dropping OSPFv3 protocol packets or disrupting the adjacency. (1) For every router on the link, create an additional inbound SA for the interface being rekeyed using a new SPI and the new key. (2) For every router on the link, replace the original outbound SA with one using the new SPI and key values. The SA replacement operation should be atomic with respect to sending OSPFv3 packets on the link so that no OSPFv3 packets are sent without authentication/encryption. (3) For every router on the link, remove the original inbound SA. Note that all the routers on the link must complete step 1 before any begin step 2. Likewise, all the routers on the link must complete step 2 before any begin step 3. One way to control the progression from one step to the next is for each router to have a configurable time constant KeyRolloverInterval. After the router begins step 1 on a given link, it waits for this interval and then moves to step 2. Likewise, after moving to step 2, it waits for this interval and then moves to step 3. In order to achieve smooth key transition, all the routers on a link should use the same value for KeyRolloverInterval, and should initiate the key rollover process within this time period. At the end of this procedure, all the routers will have a single inbound and outbound SA for OSPFv3 on the link with the new SPI and key values. 11. IPsec rules The following set of transport mode rules can be installed in a typical IPsec implementation to provide the authentication/confidentiality to OSPFv3 packets. Outbound Rules for interface running OSPFv3 security: M. Gupta/N. Melam Expires - April 2005 [Page 8]
Internet Draft Authentication/Confidentiality to OSPFv3 October 2004 No. source destination protocol action 1 fe80::/10 any OSPF apply Outbound Rules for virtual links running OSPFv3 security: No. source destination protocol action 2 src/128 dst/128 OSPF apply Inbound Rules for interface running OSPFv3 security: No. source destination protocol action 3 fe80::/10 any ESP/OSPF or AH/OSPF apply 4 fe80::/10 any OSPF drop Inbound Rules for virtual links running OSPFv3 security: No. source destination protocol action 5 src/128 dst/128 ESP/OSPF or AH/OSPF apply 6 src/128 dst/128 OSPF drop For outbound rules, action "apply" means encrypting/calculating ICV and adding ESP or AH header. For inbound rules, action "apply" means decrypting/authenticating the packets and stripping ESP or AH header. Rules 4 and 6 are to drop the insecure OSPFv3 packets without ESP/AH headers. ESP/OSPF or AH/OSPF in rules 3 and 5 mean that it is an OSPF packet secured with ESP or AH. Rules 1, 3 and 4 are meant to secure the unicast and multicast OSPF packets that are not being exchanged over the virtual links. These rules MUST be installed only in the security policy database (SPD) of the interface running OSPFv3 security. Rules 2, 5 and 6 are meant to secure the packets being exchanged over virtual links. These rules are dynamically installed after learning the end point IP addresses of a virtual link. These rules MUST be installed on at least the interfaces that are connected to the transit area for the virtual link. These rules MAY alternatively be installed on all the interfaces. If these rules are not installed on all the interfaces, clear text or malicious OSPFv3 packets with same source and destination addresses as virtual link end point addresses will be delivered to OSPFv3. Though OSPFv3 drops these packets because they were not received on the right interface, OSPFv3 receives some clear text or malicious packets even when the security is on. Installing these rules on all the interfaces insures that M. Gupta/N. Melam Expires - April 2005 [Page 9]
Internet Draft Authentication/Confidentiality to OSPFv3 October 2004 OSPFv3 does not receive these clear text or malicious packets when security is turned on. On the other hand installing these rules on all the interfaces increases the processing overhead on the interfaces where there is no IPsec processing otherwise. The decision of installing these rules on all the interfaces or on just the interfaces that are connected to the transit area is a private decision and doesn't affect the interoperability in any way. So this decision is left to the implementers. 12. Mandatory Encryption and Authentication Algorithms The implementation MUST allow the user to choose AES-CBC as the encryption algorithm and HMAC-SHA1 as the authentication algorithm for securing OSPFv3 packets. The implementation MUST NOT allow the user to choose stream ciphers as the encryption algorithm for securing OSPFv3 packets as the stream ciphers are not suitable for manual keys. 13. Replay Protection As it is not possible as per the current standards to provide complete replay protection while using manual keying, the proposed solution will not provide protection against replay attacks. Fields LS age, LS Sequence Number and LS checksum in LSA header are kept intact in OSPFv3. Though these fields do not provide the complete protection, they certainly help against replay attacks. Security Considerations This memo discusses the use of IPsec AH and ESP headers in order to provide security to OSPFv3 for IPv6. Hence security permeates throughout this document. This specification mandates the usage of manual keys. The following are the known limitations of the usage of manual keys. O Manual keys are usually long lived (changing them very often is a tedious task). This gives an attacker enough time to discover the keys. O As the administrator is manually configuring the keys, there is a chance that the configured keys are weak (there are known weak keys for DES/3DES at least). M. Gupta/N. Melam Expires - April 2005 [Page 10]
Internet Draft Authentication/Confidentiality to OSPFv3 October 2004 O As the sequence numbers can not be negotiated, replay protection can not be provided. Inspite of the above known limitations, the security provided by the usage of the manual keys should be adequate for a routing protocol. Normative References N1. Moy, J., "OSPF version 2", RFC 2328, April 1998 N2. Coltun, R., Ferguson, D. and J. Moy, "OSPF for IPv6", RFC 2740, December 1999 N3. Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC XXXX, date [Note to RFC-Editor: Replace XXXX with the number of the RFC 2401 replacement]. N4. Kent, S., "IP Encapsulating Security Payload (ESP)", RFC XXXY, date [Note to RFC-Editor: Replace XXXY with the number of the RFC 2406 replacement]. N5. Kent, S., "IP Authentication Header (AH)", RFC XXXZ, date [Note to RFC-Editor: Replace XXXZ with the number of the RFC 2402 replacement]. N6. Eastlake, D., "Cryptographic Algorithm Implementation Requirements For ESP And AH", RFC XXYY, date [Note to RFC-Editor: Replace XXYY with the number of the RFC that the draft draft-ietf-ipsec-esp-ah- algorithms-02.txt gets]. N7. Bradner, S., "Key words for use in RFCs to Indicate Requirement Level", BCP 14, RFC 2119, March 1997. Informative References I1. Kaufman, C., "The Internet Key Exchange (IKEv2) Protocol", RFC XXZZ, date [Note to RFC-Editor: Replace XXZZ with the number of the RFC 2409 replacement]. Acknowledgments Authors would like to extend sincere thanks to Marc Solsona, Janne Peltonen, John Cruz, Dhaval Shah, Abhay Roy and Paul Wells for providing useful information and critiques in order to write this memo. M. Gupta/N. Melam Expires - April 2005 [Page 11]
Internet Draft Authentication/Confidentiality to OSPFv3 October 2004 We would also like to thank IPsec and OSPF WG people to provide valuable review comments. Authors' Addresses Mukesh Gupta Nokia 313 Fairchild Drive Mountain View, CA 94043 Phone: 650-625-2264 Email: Mukesh.Gupta@nokia.com Nagavenkata Suresh Melam Nokia 313 Fairchild Drive Mountain View, CA 94043 Phone: 650-625-2949 Email: Nagavenkata.Melam@nokia.com Full copyright statement Copyright (C) The Internet Society (2004). 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 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. 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 M. Gupta/N. Melam Expires - April 2005 [Page 12]
Internet Draft Authentication/Confidentiality to OSPFv3 October 2004 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. M. Gupta/N. Melam Expires - April 2005 [Page 13]
