Internet Draft IS-IS HMAC SHA Cryptographic Authentication February 2007 Network Working Group Manav Bhatia Internet Draft Lucent Technologies Expires: August 2007 Vishwas Manral IP Infusion Russ White Cisco Systems IS-IS HMAC SHA Cryptographic Authentication draft-ietf-isis-hmac-sha-01.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 3567. Although this document has been written specifically for using MAC 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 and White Expires August 2007 [Page 1] Internet Draft IS-IS HMAC SHA Cryptographic Authentication February 2007 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] 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 3567 [RFC3567] 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 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. 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. 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. Bhatia, Manral and White Expires August 2007 [Page 2] Internet Draft IS-IS HMAC SHA Cryptographic Authentication February 2007 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. 3. Authentication Procedures 3.1 Authentication TLV A new authentication code, [TB assigned by IANA], 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 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. Bhatia, Manral and White Expires August 2007 [Page 3] Internet Draft IS-IS HMAC SHA Cryptographic Authentication February 2007 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 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 authentication value field is set to Zero. 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. 3.3 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. These fields are set to Zero and the authentication data is computed. The calculated data is compared with the received 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. Bhatia, Manral and White Expires August 2007 [Page 4] Internet Draft IS-IS HMAC SHA Cryptographic Authentication February 2007 Similarly, implementations not supporting the CRYPTO_AUTH field MAY accept PDUs that contain this particular field in TLV 10. 4. Algorithm Dependent Processing HMAC is a mechanism for message authentication using cryptographic hash functions and has been explained in depth in [RFC2104]. The reader is suggested to go through it to clearly understand how it works. HMAC can be used, without modifying any hash function, for calculating and verifying the message authentication values. It thus verifies both the data integrity and the authenticity of a message. The HMAC algorithm takes key K and text T as the input. The block size B is 64 for SHA-1, SHA-224 and SHA-256 and its 128 for SHA-384 and SHA-512 The Key K is the password that has been chosen and text T is the IS- IS PDU that needs to be authenticated. Because of the way the hash functions are used in HMAC construction, the collision attacks currently known against MD5 [MD5-attack] and SHA-1 [SHA-1-attack] do not apply. 5. 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 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. Bhatia, Manral and White Expires August 2007 [Page 5] Internet Draft IS-IS HMAC SHA Cryptographic Authentication February 2007 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. There are certain hash functions that require all the fields of the message text T to be filled with non zero values. Any extension using such hash functions to calculate the HMAC MUST fill the life time, checksum and the authentication value field of the TLV with some pre- defined non zero random number. 6. Acknowledgements We would like to thank Ran Atkinson and Tony Li for their comments and their earlier work on IS-IS authentication from which this draft has been derived. Thanks to Hugo Krawczyk, Arjen K. Lenstra (Bell Labs), Eric Grosse (Bell Labs) and Matthew J. Fanto (NIST) for educating us on some of the finer points related to Crypto Mathematics. 7. IANA Considerations IANA needs to give value for the CRYPTO_AUTH field in the authentication TLV 10. This document currently defines a value of 2 to be used to denote CRYPTO_AUTH mechanism for authenticating IS-IS PDUs. 8. References 8.1 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 [RFC3567] Li, T. and R. Atkinson, "Intermediate System to Intermediate System (IS-IS) Cryptographic Authentication", RFC 3567, July 2003 [RFC2104] Krawczyk, H. et al., "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, February 1997 Bhatia, Manral and White Expires August 2007 [Page 6] Internet Draft IS-IS HMAC SHA Cryptographic Authentication February 2007 [NIST] National Institute of Standards and Technology, "Secure Hash Standard", FIPS PUB 180-2, August 2002 8.2 Informative References [MD5-attack] Wang, X. et al., "Collisions for Hash Functions MD4, MD5, HAVAL-128 and RIPEMD", August 2004, http://eprint.iacr.org/2004/199 [SHA-1-attack] Wang, X. et al., "Collision Search Attacks on SHA1", February 2005, http://theory.csail.mit.edu/~yiqun/shanote.pdf [CRYPTO] Manral, V. et al., "Issues with existing Cryptographic Protection Methods for Routing Protocols", Work in Progress, February 2006 9. Author's Addresses Manav Bhatia Alcatel-Lucent Bangalore, India Email: manav@alcatel-lucent.com Vishwas Manral IP Infusion Almora, Uttarakhand India Email: vishwas@ipinfusion.com Russ White Cisco Systems RTP North Carolina USA Email: riw@cisco.com Full Copyright Statement Copyright (C) The IETF Trust (2007). 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. 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