[IPsec] comments on draft-ietf-ipsecme-aes-ctr-ikev2-05.txt

The statement that "Although the [RFC4307] specifies that the AES-CTR  
encryption algorithm feature SHOULD be supported by IKEv2, no existing  
document specifies how IKEv2 can support the feature"  is not  
completely correct.  RFC 5282 specifies how to use AES in the Galois  
Counter Mode (GCM) and Counter and CBC-MAC (CCM) modes of operation.

Neither this draft nor RFC 4307 provides any rationale for why or when  
AES-CTR should be used.  If it is  considered useful because CTR can  
be pipelined or implemented in parallel, then the considerations of http://tools.ietf.org/html/draft-mcgrew-esp-ah-algo-update-00#section-3 
  would apply.  What value is there is promoting the use of AES-CTR  
when better technical alternatives exist and are on standards track?   
If the sole motivation for this standard is to correct the  
inconsistency between RFC 4307 and RFC 3686, then the draft should  
include a statement to that effect, and mention the IKEv2 transforms  
that have all of the advantages of AES-CTR already exist.

The draft is not very clear on how AES-CTR is supposed to be  
implemented.  What is the counter format and what is the increment  
function?   If the intent is to copy RFC 3686 then this needs to be  
made more explicit.

David

On Mar 3, 2010, at 9:51 AM, Paul Hoffman wrote:

>> A New Internet-Draft is available from the on-line Internet-Drafts
>> directories.
>> This draft is a work item of the IP Security Maintenance and  
>> Extensions Working Group of the IETF.
>>
>> 	Title		: Using Advanced Encryption Standard (AES) Counter Mode  
>> with IKEv2
>> 	Author(s)	: S. Shen, Y. Mao, S. murthy
>> 	Filename	: draft-ietf-ipsecme-aes-ctr-ikev2-05.txt
>> 	Pages		: 10
>> 	Date		: 2010-3-2
>> 	
>> This document describes the usage of Advanced Encryption Standard
>>  Counter Mode (AES-CTR), with an explicit initialization vector, by
>>  IKEv2 for encrypting the IKEv2 exchanges that follow the IKE_SA_INIT
>>  exchange.
>>
>> A URL for this Internet-Draft is:
>> http://www.ietf.org/internet-drafts/draft-ietf-ipsecme-aes-ctr-ikev2-05.txt
>
> Based on Pasi's AD review, the authors significantly shortened the  
> document. It seems prudent to have the WG review the new, shorter  
> version. In particular, it would be good for developers to look at  
> the new short document and see if it is complete enough to implement  
> from.
>
> This review cycle will end in a week, but please do the review early  
> in case problems are found.
>
> --Paul Hoffman, Director
> --VPN Consortium
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