KARP Working Group Manav Bhatia Internet Draft Alcatel-Lucent Intended status: Standards Track Vishwas Manral Expires: March, 2011 IP Infusion September 2010 Supporting Authentication Trailer for OSPFv3 draft-bhatia-manral-auth-trailer-ospfv3-00.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and 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." 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Bhatia and Manral Standards Track [Page 1] Internet-Draft September 2010 Abstract Currently OSPFv3 uses IPsec for authenticating the protocol packets. There however are some environments (mobile ad-hoc), where IPsec is difficult to configure and maintain, and this mechanism cannot be used. This draft proposes an alternative mechanism that can be used so that OSPFv3 does not depend upon IPsec for security. 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. [RFC2119] Table of Contents 1. Introduction..................................................2 2. Basic Operation...............................................4 3. OSPFv3 Security Association...................................5 4. Authentication Procedure......................................6 4.1. Authentication Trailer...................................6 4.2. Cryptographic Authentication Procedure...................7 4.3. Cryptographic Aspects....................................8 4.4. Message Verification....................................10 5. Security Considerations......................................10 6. IANA Considerations..........................................11 7. References...................................................11 7.1. Normative References....................................11 7.2. Informative References..................................11 1. Introduction Unlike OSPF (Open Shortest Path First) Version 2 [RFC2328] OSPF for IPv6 (OSPFv3) [RFC5340], does not have Auth Type and Authentication fields in its headers for authenticating the protocol packets. It instead relies on the IPv6 Authentication Header (AH) [RFC4302] and IPv6 Encapsulating Security Payload (ESP) [RFC4303] to provide integrity, authentication, and/or confidentiality. Bhatia and Manral Expires March 2011 [Page 2] Internet-Draft September 2010 [RFC4552] describes how IPv6 AH/ESP extension headers can be used to provide authentication/confidentiality to OSPFv3. There however are some environments (mobile ad-hoc), where IPsec is difficult to configure and maintain, and this mechanism cannot be used. There is also an issue with IPsec not being available on some platforms or it requiring some additional license which may be expensive. [RFC4552] discusses, at length, the reasoning behind using manually configured keys, rather than some automated key management protocol such as IKEv2 [RFC5996]. The primary problem is the lack of suitable key management mechanism, as OSPF adjacencies are formed on a one-to-many basis and most key management mechanisms are designed for a one-to-one communication model. This forces the system administrator to use manually configured security associations (SAs) and cryptographic keys to provide the authentication and, if desired, confidentiality services. Regarding replay protection [RFC4552] states that: 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. Since there is no replay protection provided there are a number of vulnerabilities in OSPFv3 which have been discussed in [crypto-issues]. OSPFv3 uses IPsec for data integrity and rarely employs it for confidentiality, therefore [RFC4552] mandates the use of ESP- NULL. Since there is no deterministic way to differentiate between encrypted and unencrypted ESP packets by simply examining the packet, it could become tricky for some implementations to prioritize certain OSPFv3 packets (Hellos for example) over the others. This draft proposes a new mechanism that works similar to OSPFv2 for providing authentication to the OSPFv3 packets and attempts to solve the problems described above for OSPFv3. Additionally this document describes how HMAC-SHA authentication can be used for OSPFv3. Bhatia and Manral Expires March 2011 [Page 3] Internet-Draft September 2010 By definition, HMAC ([RFC2104], [FIPS-198]) requires a cryptographic hash function. This document proposes to use any one of SHA-1, SHA-256, SHA-384, or SHA-512 [FIPS-180-3] to authenticate the OSPFv3 packets. It is believed that [RFC2104] is mathematically identical to [FIPS-198] and it is also believed that algorithms in [RFC4634] are mathematically identical to [FIPS-180-3]. 2. Basic Operation The OSPFv3 authentication information is appended to the OSPFv3 packet and is not actually considered part of the OSPFv3 protocol packet. Thus the authentication information is not included in the OSPFv3 header's packet length, but is instead included in the IPv6 packet's payload length. This is very similar to how the message digest is carried in the OSPFv2 packet. The only difference between this mechanism and OSPFv2's authentication mechanism is that for OSPFv3 we carry some more authentication information in addition to the message digest. The additional information carried is detailed in the next section. Packet format before applying Authentication: +----------------+-----------------+ |orig IP header | OSPFv3 Payload | |(any options) | | +----------------+-----------------+ Packet format after applying Authentication: +----------------+----------------+-----------------+ |orig IP header | OSPFv3 Payload | Authentication | |(any options) | | Trailer | +----------------+----------------+-----------------+ The procedure followed for computing the Authentication trailer is exactly the same as described in [RFC5709] and [RFC2328]. Bhatia and Manral Expires March 2011 [Page 4] Internet-Draft September 2010 3. OSPFv3 Security Association An OSPFv3 Security Association contains a set of parameters shared between any two legitimate OSPFv3 speakers. Parameters associated with an OSPFv3 SA: Key Identifier (Key ID) This is a 32-bit unsigned integer used to uniquely identify an OSPFV3 SA, as manually configured by the network operator. The receiver determines the active SA by looking at the Key ID field in the incoming protocol packet. The sender based on the active configuration, selects the Security Association to use and puts the correct Key ID value associated with the Security Association in the OSPFV3 protocol packet. If multiple valid and active OSPFV3 Security Associations exist for a given outbound interface at the time an OSPFV3 packet is sent, the sender may use any of those security associations to protect the packet. Using Key IDs makes changing keys while maintaining protocol operation convenient. Each key ID specifies two independent parts, the authentication protocol and the authentication key, as explained below. Normally, an implementation would allow the network operator to configure a set of keys in a key chain, with each key in the chain having fixed lifetime. The actual operation of these mechanisms is outside the scope of this document. Note that each key ID can indicate a key with a different authentication protocol. This allows multiple authentication mechanisms to be used at various times without disrupting an OSPFv3 peering, including the introduction of new authentication mechanisms. Authentication Algorithm This signifies the authentication algorithm to be used with the OSPFv3 SA. This information is never sent in cleartext over the wire. Because this information is not sent on the wire, the implementer chooses an implementation specific representation for this information. Bhatia and Manral Expires March 2011 [Page 5] Internet-Draft September 2010 At present, the following values are possible: HMAC-SHA-1, HMAC-SHA-256, HMAC-SHA-384 and HMAC-SHA-512. Authentication Key This value denotes the cryptographic authentication key associated with the OSPFv3 SA. The length of this key is variable and depends upon the authentication algorithm specified by the OSPFv3 SA. 4. Authentication Procedure 4.1. Authentication Trailer The authentication trailer that is appended to the OSPFv3 protocol packet is described below: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0 | Key ID | Auth Data Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Cryptographic Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Authentication Data (Variable) | ~ ~ | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 The idea is to keep the fields as similar as possible with OSPFv2 so that most of the source code can be reused for authenticating the OSPFv3 protocol packets. The various fields in the Authentication trailer are: Reserved 16-bit reserved field. The value MUST be initialized to zero by the sender, and MUST be ignored by the receiver. Bhatia and Manral Expires March 2011 [Page 6] Internet-Draft September 2010 Key ID (Identifier) 32-bit field that identifies the algorithm and the secret key used to create the message digest appended to the OSPFv3 protocol packet. Key Identifiers are unique per-interface. Cryptographic Sequence Number 32-bit non-decreasing sequence number that is used to guard against replay attacks. Authentication Data Variable data that is carrying the digest of the protocol packet. 4.2. Cryptographic Authentication Procedure As noted earlier the algorithms used to generate and verify the message digest are specified implicitly by the secret key. This specification discusses the computation of OSPFv3 Cryptographic Authentication data when any of the NIST SHS family of algorithms is used in the Hashed Message Authentication Code (HMAC) mode. The currently valid algorithms (including mode) for OSPFv3 Cryptographic Authentication include: HMAC-SHA-1 HMAC-SHA-256 HMAC-SHA-384 HMAC-SHA-512 Of the above, implementations of this specification MUST include support for at least: HMAC-SHA-256 and SHOULD include support for: HMAC-SHA-1 and MAY also include support for: HMAC-SHA-384 HMAC-SHA-512 Bhatia and Manral Expires March 2011 [Page 7] Internet-Draft September 2010 4.3. Cryptographic Aspects In the algorithm description below, the following nomenclature, which is consistent with [FIPS-198], is used: H is the specific hashing algorithm (e.g. SHA-256). K is the Authentication Key for the OSPFv3 security association. Ko is the cryptographic key used with the hash algorithm. B is the block size of H, measured in octets rather than bits. Note that B is the internal block size, not the hash size. For SHA-1 and SHA-256: B == 64 For SHA-384 and SHA-512: B == 128 L is the length of the hash, measured in octets rather than bits. XOR is the exclusive-or operation. Opad is the hexadecimal value 0x5c repeated B times. Ipad is the hexadecimal value 0x36 repeated B times. Apad is the hexadecimal value 0x878FE1F3 repeated (L/4) times. Implementation Note: This definition of Apad means that Apad is always the same length as the hash output. (1)Preparation of the Key In this application, Ko is always L octets long. If the Authentication Key (K) is L octets long, then Ko is equal to K. If the Authentication Key (K) is more than L octets long, then Ko is set to H(K). If the Authentication Key (K) is less than L octets long, then Ko is set to the Authentication Key (K) with zeros appended to the end of the Authentication Key (K) such that Ko is L octets long. (2)First Hash First, the OSPFv3 packet's Authentication Trailer (which is very similar to the appendage described in RFC 2328, Section D.4.3, Page 233, items(6)(a) and (6)(d)) is filled with the value Apad. Bhatia and Manral Expires March 2011 [Page 8] Internet-Draft September 2010 Then, a First-Hash, also known as the inner hash, is computed as follows: First-Hash = H(Ko XOR Ipad || (OSPFv3 Packet)) Implementation Notes: Note that the First-Hash above includes the Authentication Trailer containing the Apad value, as well as the OSPFv3 packet, as per RFC 2328, Section D.4.3. The definition of Apad (above) ensures it is always the same length as the hash output. This is consistent with RFC 2328. The "(OSPFv3 Packet)" mentioned in the First-Hash (above) does include the OSPF Authentication Trailer. The digest length for SHA-1 is 20 bytes; for SHA-256, 32 bytes; for SHA-384, 48 bytes; and for SHA-512, 64 bytes. (3)Second Hash Then a second hash, also known as the outer hash, is computed as follows: Second-Hash = H(Ko XOR Opad || First-Hash) (4)Result The resulting Second-Hash becomes the authentication data that is sent in the Authentication Trailer of the OSPFv3 packet. The length of the authentication data is always identical to the message digest size of the specific hash function H that is being used. This also means that the use of hash functions with larger output sizes will also increase the size of the OSPFv3 packet as transmitted on the wire. Implementation Note: RFC 2328, Appendix D specifies that the Authentication Trailer is not counted in the OSPF packet's own Length field, but is included in the packet's IP Length field. Similar to this, the Authentication Trailer is not included in OSPFv3's own Length field, but is included in IPv6's payload length. Bhatia and Manral Expires March 2011 [Page 9] Internet-Draft September 2010 4.4. Message Verification An incoming router would implicitly know that OSPFv3 non IPsec cryptographic authentication is in use if it finds that the length indicated by the IPv6 header is more than the packet length given in the OSPFv3 header. Authentication algorithm dependent processing needs to be performed, using the algorithm specified by the appropriate OSPFv3 SA for the received packet. Before an implementation performs any processing it needs to save the values of the Authentication data field from the Authentication trailer appended to the OSPFv3 packet. It should then set the Authentication data field with Apad before the authentication data is computed. The calculated data is compared with the received authentication data in the Authentication trailer and the packet is discarded if the two do not match. In such a case, an error event SHOULD be logged. An implementation MAY have a transition mode where it includes the Authentication Trailer in the packets but does not verify this information. This is provided as a transition aid for networks in the process of migrating to the mechanism described in this draft. 5. Security Considerations The document proposes extensions to OSPFv3 which would make it more secure than what it is today. It does not provide confidentiality as a routing protocol contains information that does not need to be kept secret. It does, however, provide means to authenticate the sender of the packets which is of interest to us. It should be noted that authentication method described in this document is not being used to authenticate the specific originator of a packet, but is rather being used to confirm that the packet has indeed been issued by a router which had access to the password. The mechanism described here is not perfect and does not need to be perfect. Instead, this mechanism represents a significant increase in the work function of an adversary attacking the OSPFv3 protocol, while not causing undue implementation, deployment, or operational complexity. Bhatia and Manral Expires March 2011 [Page 10] Internet-Draft September 2010 There is a transition mode suggested where routers can ignore the Generic Authentication extension header information carried in the protocol packets. The operator must ensure that this mode is only used when migrating to the new Generic Authentication based scheme as this leaves the router vulnerable to an attack. 6. IANA Considerations The Generic Authentication extension header number is assigned by IANA out of the IP Protocol Number space (and as recorded at the IANA web page at http://www.iana.org/assignments/protocol-numbers) is: TBD. 7. References 7.1. Normative References [RFC2119] Bradner, S.,"Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [FIPS-180-3] US National Institute of Standards & Technology, "Secure Hash Standard (SHS)", FIPS PUB 180-3, October 2008. [FIPS-198] US National Institute of Standards & Technology, "The Keyed-Hash Message Authentication Code (HMAC)", FIPS PUB 198, March 2002. 7.2. Informative References [RFC2104] Krawczk, H., "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, February 1997. [RFC2328] Moy, J., "OSPF Version 2", RFC 2328, April 1998. [RFC5340] Coltun, R., et. al., "OSPF for Ipv6", RFC 5340, July 2008 [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December 2005. [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, December 2005. [RFC5996] Kaufman, C., et. al., "Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 5996, September 2010. Bhatia and Manral Expires March 2011 [Page 11] Internet-Draft September 2010 [RFC4552] Gupta, M. and Melam, N., "Authentication/Confidentiality for OSPFv3", RFC 4552, June 2006 [RFC4634] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms (SHA and HMAC-SHA)", RFC 4634, July 2006. [RFC5709] Bhatia, M., et. al.,"OSPFv2 HMAC-SHA Cryptographic Authentication", RFC 5709, October 2009 [crypto-issues] Bhatia, M., et. al., "Issues with existing Cryptographic Protection Methods for Routing Protocols", Work in Progress Author's Addresses Manav Bhatia Alcatel-Lucent Bangalore India Email: manav.bhatia@alcatel-lucent.com Vishwas Manral IP Infusion USA Email: vishwas@ipinfusion.com Bhatia and Manral Expires March 2011 [Page 12]