Internet Draft IS-IS Generic Cryptographic Authentication October 2008 Network Working Group Manav Bhatia Internet Draft Alcatel-Lucent Expires: March 2009 Vishwas Manral IP Infusion (Editors) IS-IS Generic Cryptographic Authentication draft-ietf-isis-hmac-sha-05.txt Status of this Memo Distribution of this memo is unlimited. 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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document proposes an extension to IS-IS to allow the use of any cryptographic authentication algorithm in addition to the already documented authentication schemes, described in the base specification and RFC 5304. Although this document has been written specifically for using HMAC construct along with the SHA family of cryptographic hash functions, the method described in this document is generic and can be used to extend IS-IS to support any cryptographic hash function in the future. Bhatia, Manral, et. al. Expires March 2009 [Page 1]
Internet Draft IS-IS Generic Cryptographic Authentication October 2008 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. [KEYWORDS] Contents 1. Introduction...................................................2 2. IS-IS Security Association.....................................3 3. Authentication Procedures......................................4 3.1 Authentication TLV.........................................4 Figure 1..........................................................4 3.2 Authentication Process.....................................4 3.3 Cryptographic Aspects......................................4 3.4 Procedures at the Sending Side.............................6 3.5 Procedure at the Receiving Side............................6 4. Security Considerations........................................7 5. Acknowledgements...............................................8 6. IANA Considerations............................................8 7. References.....................................................9 7.1 Normative References.......................................9 7.2 Informative References.....................................9 8. Author's Addresses............................................10 1. Introduction IS-IS [ISO] [RFC1195] specification allows for authentication of its PDUs via the authentication TLV 10 that is carried as the part of the PDU. The base spec has provision for only clear text passwords and RFC 5304 [RFC5304] augments this to provide the capability to use HMAC MD5 authentication for its PDUs. The first octet of value field of TLV 10 specifies the type of authentication to be carried out. Type 0 is reserved, Type 1 indicates a cleartext password, Type 54 indicates HMAC MD5 and Type 255 is used for routing domain private authentication methods. The remainder of the value field contains the actual authentication data determined by the value of the authentication type. This document proposes a new authentication type to be carried in TLV 10, called the generic cryptographic authentication (CRYPTO_AUTH). This can be used to specify any authentication algorithm for authenticating and verifying IS-IS PDUs. This document also explains how HMAC-SHA authentication can be used in IS-IS. Bhatia, Manral, et. al. Expires March 2009 [Page 2]
Internet Draft IS-IS Generic Cryptographic Authentication October 2008 By definition, HMAC [RFC2104] requires a cryptographic hash function. We propose to use any one of SHA-1, SHA-224, SHA-256, SHA-384 and SHA-512 [NIST] for this purpose to authenticate the IS-IS PDUs. We propose to do away with the per interface keys and instead have key IDs that map to unique IS-IS Security Associations. While there are no openly published attacks on the HMAC-MD5 mechanism, some reports [Dobb96a, Dobb96b] create concern about the ultimate strength of the MD5 cryptographic hash function. 2. IS-IS Security Association An IS-IS Security Association (SA) contains a set of shared parameters between any two legitimate IS-IS speakers. Parameters associated with an IS-IS SA: o Key ID : This is a one octet unsigned integer used to uniquely identify an IS-IS SA, as manually configured by the network operator. The receiver determines the active SA by looking at this field in the incoming PDU. The sender puts this Key ID based on the active configuration. 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 IS-IS peering, including the introduction of new authentication mechanisms. o Authentication Algorithm : This signifies the authentication algorithm to be used with the IS-IS SA. Valid values are HMAC-SHA-1, HMAC-SHA-224, HMAC-SHA-256, HMAC-SHA-384 and HMAC-SHA-512. o Authentication Key : This value denotes the key associated with the IS-IS SA. The length of this key is variable and depends upon the authentication algorithm specified by the IS-IS SA. Bhatia, Manral, et. al. Expires March 2009 [Page 3]
Internet Draft IS-IS Generic Cryptographic Authentication October 2008 3. Authentication Procedures 3.1 Authentication TLV A new authentication code, 0x3, indicates the CRYPTO_AUTH mechanism described in this document is in use, is inserted in the first octet of the existing IS-IS Authentication TLV (10). 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type 10 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Auth Type | Key ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | Authentication Data (Variable)| + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 3.2 Authentication Process When calculating the CRYPTO_AUTH result for Sequence Number PDUs, Level 1 Sequence Number PDUs SHALL use the Area Authentication string as in Level 1 Link State PDUs. Level 2 Sequence Number PDUs shall use the domain authentication string as in Level 2 Link State PDUs. IS-IS HELLO PDUs SHALL use the Link Level Authentication String, which MAY be different from that of Link State PDUs. The CRYPTO_AUTH result for the IS-IS HELLO PDUs SHALL be calculated after the PDU is padded to the MTU size, if padding is not disabled. Implementations that support the optional checksum for the Sequence Number PDUs and IS-IS HELLO PDUs MUST NOT include the Checksum TLV. 3.3 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 password for the PDU type as per ISO 10589. 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. Bhatia, Manral, et. al. Expires March 2009 [Page 4]
Internet Draft IS-IS Generic Cryptographic Authentication October 2008 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. (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 IS-IS packet's Authentication Data field is filled with the value Apad and the Authentication Type field is set to 0x3. Then, a first hash, also known as the inner hash, is computed as follows: First-Hash = H(Ko XOR Ipad || (IS-IS PDU)) (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 result Second-Hash becomes the Authentication Data that is sent in the Authentication Data field of the IS-IS PDU. The length of the Authentication Data field 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 IS-IS PDU as transmitted on the wire. Bhatia, Manral, et. al. Expires March 2009 [Page 5]
Internet Draft IS-IS Generic Cryptographic Authentication October 2008 3.4 Procedures at the Sending Side An appropriate IS-IS SA is selected for use with an outgoing IS-IS PDU. This is done based on the active key at that instant. If IS-IS is unable to find an active key, then the PDU is discarded. If IS-IS is able to find the active key, then the key gives the authentication algorithm (HMAC-SHA-1, HMAC-SHA-224, HMAC-SHA-256, HMAC-SHA-384 or HMAC-SHA-512) that needs to be applied on the PDU. An implementation MUST fill the authentication type and the length before the authentication data is computed. The authentication data is computed as explained in the previous section. The length of the TLV is set as per the authentication algorithm that is being used. It's set to 22 for HMAC-SHA-1, 30 for HMAC-SHA-224, 34 for HMAC-SHA- 256, 50 for HMAC-SHA-384 and 66 for HMAC-SHA-512. Note that one octet has been added to account for the Key ID and one octet for the authentication type. The key ID is filled. The Checksum and Remaining Life time fields are set to Zero for the LSPs before authentication is calculated. The result of the authentication algorithm is placed in the Authentication data, following the key ID. The authentication data for the IS-IS IIH PDUs MUST be computed after the IIH has been padded to the MTU size, if padding is not explicitly disabled. 3.5 Procedure at the Receiving Side The appropriate IS-IS SA is identified by looking at the Key ID from the Authentication TLV 10 from the incoming IS-IS PDU. Authentication algorithm dependent processing, needs to be performed, using the algorithm specified by the appropriate IS-IS SA for the received packet. Before an implementation performs any processing it needs to save the values of the Authentication Value field, the Checksum and the Remaining Life time. It should then set the Authentication Value field with Apad and zero the Checksum and Remaining Life time fields before the authentication data is computed. The calculated data is compared with the received Bhatia, Manral, et. al. Expires March 2009 [Page 6]
Internet Draft IS-IS Generic Cryptographic Authentication October 2008 authentication data in the PDU and the PDU 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 CRYPTO_AUTH information in the PDUs but does not verify this information. This is provided as a transition aid for networks in the process of migrating to the new CRYPTO_AUTH based authentication schemes. Similarly, implementations not supporting the CRYPTO_AUTH field MAY accept PDUs that contain this particular field in TLV 10. 4. Security Considerations The document proposes extensions to IS-IS 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 PDUs which is of interest to us. The technology in this document provides an authentication mechanism for IS-IS. 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 IS-IS protocol, while not causing undue implementation, deployment, or operational complexity. The mechanism detailed in this document does not protect IS-IS against replay attacks. An adversary could in theory replay old IIHs and bring down the adjacency [CRYPTO] or replay old CSNPs and PSNPs that would cause a flood of LSPs in the network. Using some sort of crypto sequence numbers in IS-IS IIHs and CSNP/PSNPs is an option to solve this problem. Discussing this is beyond the scope of this document and it's a matter which needs to be followed in the WG. This document states that the remaining lifetime of the LSP MUST be set to zero before computing the authentication, thus this field is not authenticated. This field is excluded so that the LSPs may be aged by the ISes in between without requiring to recompute the authentication data. This can be exploited by an attacker. To ensure greater security, the keys used must be changed periodically and implementations MUST be able to store and use more than one key at the same time. It should be noted that the cryptographic strength of the HMAC depends upon the cryptographic strength of the underlying hash function and on the size and quality of the key. Bhatia, Manral, et. al. Expires March 2009 [Page 7]
Internet Draft IS-IS Generic Cryptographic Authentication October 2008 If a stronger authentication were believed to be required, then the use of a full digital signature [RFC-2154] would be an approach that should be seriously considered. It was rejected for this purpose at this time because the computational burden of full digital signatures is believed to be much higher than is reasonable given the current threat environment in operational commercial networks. 5. Acknowledgements The authors would like to thank Hugo Krawczyk, Arjen K. Lenstra (Bell Labs) and Eric Grosse (Bell Labs) for educating us on some of the finer points related to Crypto Mathematics. We would also like to thank Bill Burr, Tim Polk, John Kelsey, and Morris Dworkin of (US) NIST for review of portions of this document that are directly derived from the closely related work on RIPv2 Cryptographic Authentication [RFC-4822]. 6. IANA Considerations This document requests that IANA create a new code point registry to administer the Authentication Type code points for TLV 10. This registry would be part of the existing IS-IS code points registry as established by [RFC-3563] and [RFC-3359]. This registry should be managed using the Designated Expert policy as described in [RFC-5226] and will be called IS-IS Authentication Type Codes. The values in the IS-IS Authentication Type Codes registry should be recorded in decimal and should only be approved after a designated expert, appointed by the IESG area director, has been consulted. The intention is that any allocation will be accompanied by a published RFC. However, the Designated Expert can approve allocations once it seems clear that an RFC will be published, allowing for the allocation of values prior to the document being approved for publication as an RFC. New items should be documented in a publicly and freely available specification. We should also have the provision of allowing external specifications to allocate and use the IS-IS Authentication Type Codes maintained by this registry. Initial values for the IS-IS Authentication Type Codes registry are given below; future assignments are to be made through Expert Review. Assignments consist of an authentication type name and its associated value. Bhatia, Manral, et. al. Expires March 2009 [Page 8]
Internet Draft IS-IS Generic Cryptographic Authentication October 2008 Authentication Type Code Value Reference ------------------------ ------ --------- Reserved 0 [ISO] Cleartext Password 1 [ISO] ISO 10589 Reserved 2 [ISO] Cryptographic Authentication 3 HMAC-MD5 Authentication 54 [RFC5304] Routeing Domain private authentication method 255 [ISO] This document currently defines and uses the value 3 to foster prestandard implementations. 7. References 7.1 Normative References [ISO] "Intermediate system to Intermediate system routeing information exchange protocol for use in conjunction with the Protocol for providing the Connectionless-mode Network Service (ISO 8473)", ISO/IEC 10589:1992 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, December 1990. [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119 [RFC5304] Li, T. and Atkinson, R. "Intermediate System to Intermediate System (IS-IS) Cryptographic Authentication", RFC 5304, October 2008. [RFC2104] Krawczyk, H. et al., "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, February 1997 [NIST] National Institute of Standards and Technology, "Secure Hash Standard", FIPS PUB 180-2, August 2002 [FIPS-198] US National Institute of Standards & Technology, "The Keyed-Hash Message Authentication Code (HMAC)", FIPS PUB 198, March 2002. 7.2 Informative References [Dobb96a] Dobbertin, H, "Cryptanalysis of MD5 Compress", Technical Report, 2 May 1996. (Presented at the Rump Session of EuroCrypt 1996.) [Dobb96b] Dobbertin, H, "The Status of MD5 After a Recent Attack", Bhatia, Manral, et. al. Expires March 2009 [Page 9]
Internet Draft IS-IS Generic Cryptographic Authentication October 2008 CryptoBytes, Vol. 2, No. 2, Summer 1996. [CRYPTO] Manral, V. et al., "Issues with existing Cryptographic Protection Methods for Routing Protocols", Work in Progress, February 2006 [RFC-2154] S. Murphy, M. Badger, and B. Wellington, "OSPF with Digital Signatures", RFC 2154, June 1997. [RFC-4822] R. Atkinson, M. Fanto, "RIPv2 Cryptographic Authentication", RFC 4822, February 2007. [RFC-3359] Przygienda, T., "Reserved Type, Length and Value (TLV) Codepoints in Intermediate System to Intermediate System", RFC 3359, August 2002. [RFC-3563] Zinin, A., "Cooperative Agreement Between the ISOC/IETF and ISO/IEC Joint Technical Committee 1/Sub Committee 6 (JTC1/SC6) on IS-IS Routing Protocol Development", RFC 3563, July 2003. [RFC-5226] Narten, T. and Alvestrand, H., "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, May 2008. 8. Author's Addresses Manav Bhatia Alcatel-Lucent Bangalore, India Email: manav@alcatel-lucent.com Tony Li Cisco Systems San Jose, CA USA EMail: tli@cisco.com Vishwas Manral IP Infusion Almora, Uttarakhand India Email: vishwas@ipinfusion.com Bhatia, Manral, et. al. Expires March 2009 [Page 10] Internet Draft IS-IS Generic Cryptographic Authentication October 2008 Russ White Cisco Systems RTP North Carolina USA Email: riw@cisco.com Randall J. Atkinson Extreme Networks 3585 Monroe Street Santa Clara, CA 95051 USA Email: rja@extremenetworks.com Matthew J. Fanto Ciber Inc. Dearborn, Mi USA Email: mfanto@ciber.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, Manral, et. al. Expires March 2009 [Page 11] Internet Draft IS-IS Generic Cryptographic Authentication October 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, Manral, et. al. Expires March 2009 [Page 12]
