Subject: [Hipsec] A question on the replay protection in HIP-base 08.draft

From: JiangXingFeng <[email-masked]>
Date: Tue, 31 Jul 2007 16:26:24 +0800

Hi: 
In the section 4.1.4 of draft-ietf-hip-base-08, it says that "
Implementations MUST accept puzzles from the current generation and MAY
accept puzzles from earlier generations'. 

The generation counter is designed to protect replay attack in HIP. The
initiator should not accept R1 with earlier counter, but HIP uses IP
protocol to transport message and lack of reliability, so that the R1
message MAY duplicate or out of order. From the above reason, the draft say
that "initiator MAY accept puzzles from earlier generations". Is my
understanding right? If it is not, what is the reason for that statement? 

Regards!
--
Jiang XingFeng

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From: Pekka Nikander <[email-masked]>
Date: Tue, 31 Jul 2007 11:35:10 +0300

AFAICS, your understanding is basically correct.

However, IIRC, another consideration we had in mind was very limited  
hosts.  It may be desirable to implement HIP on hosts where it is too  
costly to store the generation counter for all/some hosts.   
Furthermore, if you don't store the generation counter, you harm only  
yourself: you will become vulnerable to certain replay attacks, but  
that doesn't harm the Internet in the large.  So, in the spirit of  
doing no harm, it seemed safest to allow hosts to pick their own  
policy depending on their resources etc.

--Pekka