Re: [IPsec] I-D Action: draft-ietf-ipsecme-dh-checks-03.txt

Johannes Merkle <johannes.merkle@secunet.com> Tue, 23 April 2013 17:41 UTC

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Date: Tue, 23 Apr 2013 19:41:13 +0200
From: Johannes Merkle <johannes.merkle@secunet.com>
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Subject: Re: [IPsec] I-D Action: draft-ietf-ipsecme-dh-checks-03.txt
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I hope I am not too late as the document write-up has already been sent out.

Section 2.3 specifies:
   A receiving peer MUST check
   that its peer's public value is valid; that is, it is not the point-
   at-infinity, and that the x and y parameters from the peer's public
   value satisfy the curve equation, that is, y**2 = x**3 + ax + b mod p

How can a peer check this? I am not aware of any encoding rule for the point-at-infinity in RFC 5903 or RFC 5114. Does
the encoding of SEC1 apply, where the point-at-infinity is encoded to 0x00? According to RFC 5903 this would be padded
with zeros, so that the decoding algorithm of the receiving peer would obtain x=0 and y=0. These do certainly not
fulfill the curve equation as the discriminant -16*(4*a^3 + 27*b^2) must be non-zero.

So isn't the requirement to check that the value it is not the point-at-infinity confusing and redundant?

Johannes


> 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           : Additional Diffie-Hellman Tests for IKEv2
> 	Author(s)       : Yaron Sheffer
>                           Scott Fluhrer
> 	Filename        : draft-ietf-ipsecme-dh-checks-03.txt
> 	Pages           : 11
> 	Date            : 2013-04-22
> 
> Abstract:
>    This document adds a small number of mandatory tests required for the
>    secure operation of IKEv2 with elliptic curve groups.  No change is
>    required to IKE implementations that use modular exponential groups,
>    other than a few rarely used so-called DSA groups.  This document
>    updates the IKEv2 protocol, RFC 5996.
> 
> 
> The IETF datatracker status page for this draft is:
> https://datatracker.ietf.org/doc/draft-ietf-ipsecme-dh-checks
> 
> There's also a htmlized version available at:
> http://tools.ietf.org/html/draft-ietf-ipsecme-dh-checks-03
> 
> A diff from the previous version is available at:
> http://www.ietf.org/rfcdiff?url2=draft-ietf-ipsecme-dh-checks-03
> 
> 
> Internet-Drafts are also available by anonymous FTP at:
> ftp://ftp.ietf.org/internet-drafts/
> 
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> 


-- 

Mit freundlichen Grüßen,
Dr. Johannes Merkle
Principal Beratung, Elektronische Identitäten
Public Sector
secunet Security Networks AG
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Germany
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