Hi Paul, 

I meant implementations conforming to the RFC 4307 which implemented the group 
2. However, users must not use the group 2 because it is not secure at this 
time. 

If we want users not to use bad options, then we must prohibit them with "MUST  
NOT" for implementations. There are no reasons for saying "allowed" to 
implement them while asking users not to use them unless we want to say to 
users they are allowed to be used. 

This text "On the other hand, comments and recommendations from this document 
are also expected to be useful for such users." and the document says that  the 
groups 2 and 5 are allowed  "SHOULD NOT, not MUST NOT".  All of these seem to 
tell users that these groups are allowed to use. 

Regards,
Quynh. 


________________________________________
From: Paul Wouters <[email protected]>
Sent: Wednesday, May 11, 2016 2:15 PM
To: Dang, Quynh (Fed)
Cc: IPsecME WG
Subject: Re: [IPsec] I-D Action: draft-ietf-ipsecme-rfc4307bis-08.txt

On Wed, 11 May 2016, Dang, Quynh (Fed) wrote:

> We should explain that current MTI group is the group 2.

But it is not? The only MUST entry for Type 4 is Group 14 (modp2048)
Group 2 is SHOULD NOT.

>  However, users shall not use that group and the group. We should create a 
> similar statement for SHA1 in signatures.

What users should or should not do and what implementations offer as
default or not are out of scope for this document as explained in:

https://tools.ietf.org/html/draft-ietf-ipsecme-rfc4307bis-07#section-1.3

    The recommendations of this document mostly target IKEv2 implementers
    as implementations need to meet both high security expectations as
    well as high interoperability between various vendors and with
    different versions.  Interoperability requires a smooth move to more
    secure cipher suites.  This may differ from a user point of view that
    may deploy and configure IKEv2 with only the safest cipher suite.  On
    the other hand, comments and recommendations from this document are
    also expected to be useful for such users.

In other words, the document sets the lowest acceptable bar. An
implementation only implementing MUST algorithms is obviously
more secure than an implementation that implements SHUOLD NOT
algorithms.

Paul

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