OSPF HMAC-SHA Cryptographic Authentication

The “OSPF HMAC-SHA Cryptographic Authentication” draft co-authored by me has been accepted as a WG document.

This IETF draft describes a mechanism for authenticating OSPF packets by making use of the HMAC algorithm in conjunction with the SHA family of cryptographic hash functions. Because of the way the hash functions are used in HMAC construction, the collision attacks currently known against SHA-1 do not apply. 
So why do we need this extension?

In the cryptographic authentication scheme described in RFC 2328, the OSPF routers on a common network/subnet share a secret key which is used to generate a keyed MD5 digest for each packet while a monotonically increasing sequence number scheme is used to prevent replay attacks. 
This isnt good enough as there have been recent reports about attacks on MD5 which raises concerns about the remaining useful lifetime of this scheme. Specifically, the researchers have been able to develop algorithms that can compute hash collisions for some applications of MD5. MD5CRK, was a distributed computing project to break the MD5 hash algorithm in a short period of time. The project closed down with the publication of the paper.
It was discovered that collisions can be found in MD5 algorithm in less than 24 hours, making MD5 insecure. Further research has verified this result and shown other ways to find collisions in MD5 hashes.  It should however be noted that these attacks may not necessarily result in direct vulnerabilities in Keyed-MD5 as used in OSPF authentication purposes, because the colliding message may not  necessarily be a syntactically correct protocol packet. However, there is a need felt to move away from MD5 towards more complex and difficult to break hash algorithms. 
This document therefore adds support for HMAC  construction to be used for authenticating OSPF packets. HMAC can be used, without modifying any hash function, for calculating and verifying the message authentication values. It verifies both the data integrity and the authenticity of a message. Because of the way the hash functions are used in HMAC construction, the collision attacks    currently known against MD5 and SHA-1 do not apply. 
By definition, HMAC 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 OSPF packets. 
This document explains how HMAC-SHA-1, HMAC-SHA-224, HMAC-SHA-256, HMAC-SHA-384 and HMAC-SHA-512 shall work with OSPF. 


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