Network working group L. Zheng Internet Draft M. Chen Intended status: Standards Track Huawei Technologies Updates: RFC 5036 (if approved) Expires: April 2011 October 8, 2010 LDP Hello Cryptographic Authentication draft-zheng-mpls-ldp-hello-crypto-auth-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." 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 April 8, 2010. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Zheng, et al. Expires April 8, 2011 [Page 1] Internet-Draft LDP Hello Cryptographic Authentication October 2010 Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Abstract This document introduces a new Cryptographic Authentication TLV which is used in LDP Hello message as an optional parameter. It enhances the authentication mechanism for LDP by securing the Hello message against spoofing attack. 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. Cryptographic Authentication TLV..............................4 2.1. Optional Parameter for Hello Message.....................4 2.2. Cryptographic Authentication TLV Encoding................4 3. Processing Hello Message Using Cryptographic Authentication...5 3.1. Transmission Using Cryptographic Authentication..........6 3.2. Receipt Using Cryptographic Authentication...............6 4. Security Considerations.......................................7 5. IANA Considerations...........................................7 6. Acknowledgments...............................................8 7. References....................................................8 7.1. Normative References.....................................8 7.2. Informative References...................................8 Authors' Addresses...............................................9 1. Introduction The Label Distribution Protocol (LDP) [RFC 5036] utilizes LDP sessions that run between LDP peers. The peers may be directly connected at the link level or may be remote. A label switching router (LSR) that speaks LDP may be configured with the identity of its peers or may discover them using the LDP Hello message sent encapsulated in UDP that may be addressed to "all routers on this subnet" or to a specific IP address. Periodic Hello messages are also used to maintain the relationship between LDP peers necessary to keep the LDP session active. Zheng, et al. Expires April 8, 2011 [Page 2] Internet-Draft LDP Hello Cryptographic Authentication October 2010 Unlike all other LDP messages, the Hello messages are sent using UDP not TCP. This means that they cannot benefit from the security mechanisms available with TCP. [RFC5036] does not provide any security mechanisms for use with Hello messages except to note that some configuration may help protect against bogus discovery events. Spoofing a Hello packet for an existing adjacency can cause the valid adjacency to time out and in turn can result in termination of the associated session. This can occur when the spoofed Hello specifies a smaller Hold Time, causing the receiver to expect Hellos within this smaller interval, while the true neighbor continues sending Hellos at the previously agreed lower frequency. Spoofing a Hello packet can also cause the LDP session to be terminated directly, which can occur when the spoofed Hello specifies a different Transport Address, other than the previously agreed one between neighbors. Spoofed Hello messages is observed and reported as real problem in production networks. As described in [RFC5036], the threat of spoofed Basic Hellos can be reduced by accepting Basic Hellos only on interfaces to which LSRs that can be trusted, and ignoring Basic Hellos not addressed to the "all routers on this subnet" multicast group. Spoofing attacks via Extended Hellos are potentially more serious threat. An LSR can reduce the threat of spoofed Extended Hellos by filtering them and accepting only those originating at sources permitted by an access list. However, performing the filtering using access lists requires LSR resource, and the LSR is still vulnerable to the IP source address spoofing. This document introduces a new Cryptographic Authentication TLV which is used in LDP Hello message as an optional parameter. It enhances the authentication mechanism for LDP by securing the Hello message against spoofing attack, and an LSR can be configured to only accept Hello messages from specific peers when authentication is in use. Using this Cryptographic Authentication TLV, one or more secret keys (with corresponding key IDs) are configured in each system. For each LDP Hello packet, the key is used to generate and verify a "message digest" or "message hash" that is stored in the LDP Hello packet. A sequence number is also carried in each packet to help avoid replay attacks. Zheng, et al. Expires April 8, 2011 [Page 3] Internet-Draft LDP Hello Cryptographic Authentication October 2010 2. Cryptographic Authentication TLV 2.1. Optional Parameter for Hello Message [RFC5036] defines the encoding for the Hello message. Each Hello message contains zero or more Optional Parameters, each encoded as a TLV. Three Optional Parameters are defined by [RFC5036]: Optional Parameter Type ------------------------------- -------- IPv4 Transport Address 0x0401 Configuration Sequence Number 0x0402 IPv6 Transport Address 0x0403 This document defines a new Optional Parameter: the Cryptographic Authentication parameter. The Cryptographic Authentication TLV Encoding is described in section 2.2. 2.2. Cryptographic Authentication TLV Encoding 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|0| Auth (0x0404) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Auth Type | Auth Key ID | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Auth Key/Digest/Hash... ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - Type: 0x0404 (TBD by IANA), Cryptographic Authentication - Length: Specifying the length in octets of the value field. - Auth Type: The authentication type in use 0 - Keyed MD5 Zheng, et al. Expires April 8, 2011 [Page 4] Internet-Draft LDP Hello Cryptographic Authentication October 2010 1 - Meticulous Keyed MD5 2 - Keyed SHA1 3 - Meticulous Keyed SHA1 4 - Keyed SHA-256 5 - Keyed SHA-384 6 - Keyed SHA-512 7-255 - Reserved for future use (TBD by IANA) - Auth Key ID: The authentication key ID in use for this packet. This allows one or more keys to be active simultaneously. - Reserved: MUST be set to zero on transmit, and ignored on receipt. - Sequence Number: The sequence number for this packet, providing protection against replay attacks. The value is incremented occasionally. For Meticulous Keyed MD5 and Meticulous Keyed SHA1 Authentication, this value is incremented for each successive packet transmitted for a session. - Auth Key/Digest/Hash: This field carries the MD5/SHA1/SHA2 key digest/hash for the packet. The length of the Auth Key/Digest/Hash varies based on the cryptographic algorithm used, which is shown as below: Auth type Length ---------------------- ---------- Keyed MD5 16 bytes Meticulous Keyed MD5 16 bytes Keyed SHA1 20 bytes Meticulous Keyed SHA1 20 bytes Keyed SHA-256 32 bytes Keyed SHA-384 48 bytes Keyed SHA-512 64 bytes When calculating the digest/hash, the shared key is stored in this field, padding with trailing zeros if needed. 3. Processing Hello Message Using Cryptographic Authentication The Cryptographic Authentication mechanisms described in this draft are very similar to those used in other protocols. One or more secret keys (with corresponding key IDs) are configured in each Zheng, et al. Expires April 8, 2011 [Page 5] Internet-Draft LDP Hello Cryptographic Authentication October 2010 system. One of the keys is included in a digest or a hash calculated over the outgoing LDP Hello packet, but the Key itself is not carried in the packet. A sequence number is also carried in each packet to help avoid replay attacks. The sequence number may be incremented in a circular fashion. For most of the authentication scheme in use, the sequence number is occasionally incremented (The decision as to when to increment the sequence number is implementation dependent and outside the scope of this document). Specifically, for Meticulous Keyed MD5 and Meticulous Keyed SHA1, the sequence number is incremented on every packet. 3.1. Transmission Using Cryptographic Authentication Prior to transmitting Hello message, the Auth Type field is set to indicate the authentication type in use. The Auth Key ID field is set to the ID of the current authentication key. The Sequence Number field is set, possibly having been incremented from the last message sent according to the scheme in place. The authentication key is placed into the Auth Key/Digest field, padding with trailing zeros as necessary, for digest/hash calculation. An MD5 digest or a SHA1/SHA2 hash is calculated over the entire LDP Hello packet. The resulting digest/hash is stored in the Auth Key/Digest/Hash field prior to transmission. The secret key is replaced by the digest/hash, and MUST NOT be carried in the packet. 3.2. Receipt Using Cryptographic Authentication The receiving LSR applies acceptability criteria for received Hellos using cryptographic authentication. If the Cryptographic Authentication TLV is unknown to the receiving LSR, the received packet MUST be discarded according to Section 3.5.1.2.2 of [RFC5036]. If the Cryptographic Authentication TLV in a received Hello packet does not contain a known and acceptable Auth Type value, then the received packet MUST be discarded. If the Auth Key ID field does not match the ID of a configured authentication key, the received packet MUST be discarded. Zheng, et al. Expires April 8, 2011 [Page 6] Internet-Draft LDP Hello Cryptographic Authentication October 2010 For most of the authentication scheme in use, if the received sequence number lies outside of the range of last sequence number received to last sequence number received +(Hello Hold Time/Hello Interval) inclusive, the received packet MUST be discarded. Specifically, for Meticulous Keyed MD5 and Meticulous Keyed SHA1, if the received sequence number lies outside of the range of last sequence number received+1 to last sequence number received +(Hello Hold Time/Hello Interval) inclusive, the received packet MUST be discarded. The receiving LSR replaces the contents of the Auth Key/Digest/Hash field with the authentication key specified by the received Auth Key ID field. If the MD5 digest or SHA1/SHA2 hash of the entire LDP Hello packet is equal to the received value of the Auth Key/Digest/Hash field, the received packet is accepted for other normal checks and processing as described in [RFC5036]. Otherwise, the received packet MUST be discarded. 4. Security Considerations Section 1 of this document describes the security issues arising from the use of unsecured LDP Hello messages. In order to combat those issues, it is RECOMMENDED that all deployments use the Cryptographic Authentication TLV to secure the Hello message. The quality of the security provided by the Cryptographic Authentication TLV depends completely on the strength of the cryptographic algorithm in use, the strength of the key being used, and the correct implementation of the security mechanism in communicating LDP implementations. Also, the level of security provided by the Cryptographic Authentication TLV varies based on the authentication type used. 5. IANA Considerations IANA maintains a registry of LDP message parameters with a sub- registry to track LDP TLV Types. This document request IANA to assign a new TLV Types as follows: TLV Type Cryptographic Authentication 0x0404 (TBD) Zheng, et al. Expires April 8, 2011 [Page 7] Internet-Draft LDP Hello Cryptographic Authentication October 2010 This document also request IANA to assign a new registry titled "LDP Hello Authentication Type", its recommended values as follows: Value LDP Hello Authentication Type Name ------- ----------------------------------- 0 Keyed MD5 1 Meticulous Keyed MD5 2 Keyed SHA1 3 Meticulous Keyed SHA1 4 Keyed SHA-256 5 Keyed SHA-384 6 Keyed SHA-512 7-255 Unassigned (TBD) 6. Acknowledgments The authors would like to thank Liu Xuehu for his work on background and motivation for LDP Hello authentication. The authors also would like to thank Adrian Farrel, Thomas Nadeau and So Ning for their comments. 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. [RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP Specification", RFC 5036, October 2007. 7.2. Informative References [RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5 Signature Option", RFC 2385, August 1998. [RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M., Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic Authentication", RFC 5709, October 2009. [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection", RFC 5880, June 2010. Zheng, et al. Expires April 8, 2011 [Page 8] Internet-Draft LDP Hello Cryptographic Authentication October 2010 Authors' Addresses Lianshu Zheng Huawei Technologies Co., Ltd. Huawei Building, No.3 Xinxi Road, Hai-Dian District, Beijing 100085 China Email: verozheng@huawei.com Mach(Guoyi) Chen Huawei Technologies Co., Ltd. Huawei Building, No.3 Xinxi Road, Hai-Dian District, Beijing 100085 China Email: mach@huawei.com Zheng, et al. Expires April 8, 2011 [Page 9]