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

["Dan Harkins" <[e-mail]>]

  Hi,

  Let me take this opportunity to point out that RFC 5297 describes
an AES-CTR variant that does not have the performance benefits that
GCM has but provides nonce misuse/abuse resistance. It is a much more
robust alternative than CCM because security is not voided if the
nonce/counter happens to get reused. The robustness properties would
work well for SA failover because you don't need to worry about the
counter being reused.

  If you're not already using CCM there's really no reason to start.
It's slow and fragile and alternatives exist to address both of those
shortcomings, GCM and SIV respectively.

  regards,

  Dan.

On Mon, March 8, 2010 8:33 am, David McGrew wrote:
>
> 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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