Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ipsecme-dh-checks
Andrey Jivsov <openpgp@brainhub.org> Tue, 09 April 2013 00:20 UTC
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Date: Mon, 08 Apr 2013 17:17:43 -0700
From: Andrey Jivsov <openpgp@brainhub.org>
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To: "Scott Fluhrer (sfluhrer)" <sfluhrer@cisco.com>
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Cc: "ipsec@ietf.org" <ipsec@ietf.org>
Subject: Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ipsecme-dh-checks
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Sorry, I was scanning too quickly. I meant section 2.1 primes, the primes in the form (renaming my earlier definition) p = k*2+1. Wouldn't receiving g^k be as much of a problem as receiving 1 for the public value? No matter what my private exponent is, the shared secret will be either of the two values. On 04/08/2013 04:15 PM, Scott Fluhrer (sfluhrer) wrote: > > >> -----Original Message----- >> From: ipsec-bounces@ietf.org [mailto:ipsec-bounces@ietf.org] On Behalf >> Of Andrey Jivsov >> Sent: Monday, April 08, 2013 6:46 PM >> To: ipsec@ietf.org >> Subject: Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ipsecme-dh-checks >> >> Sec 2.2: >>> It MUST check both that the peer's public value is in range (1 < r >>> < p-1) and that r**q = 1 mod p (where q is the size of the >>> subgroup, as listed in the RFC). >> >> Would it make sense to specify a more economical test for strong prime >> groups? > > "Strong groups", that is, groups with (p-1)/2 prime, are listed in section 2.1; and yes, the test there is considerably cheaper. > >> >> If q is meant to be p = q*2+1, there are only two possibilities for the value < >> p-1 received from the peer to be in the wrong subgroup. One of them is 1, >> which is ruled out by the check above. Another one is g^q. >> It's a fixed quantity for the given modp group. Seems like a memcmp with a >> fixed quantity g^q is the best way to address the problem. > > Actually, g^q == 1; I don't think that's what you mean. > > Now, there is certainly the possibility of the value being in the wrong subgroup; but there are far more than two possibilities. Here's the entire list for strong groups: > > 1; that's rejected by the test in section 2.1 > p-1; that's also rejected by the test in section 2.1 > primitive elements; those are elements r which have order p-1. These are not rejected by the test. > > (in addition, there are KE values that don't correspond to actual group elements; 0 and values >= p; those are rejected too). > > Now, there are q-1 different primitive elements; that's more than we could reasonably list. We could specify a test to reject primitive elements; however, that test isn't cheap (it can be done cheaper than the full r**q==1 test, nevertheless, not cheaply. In addition, an attacker injecting a primitive element could use it to deduce the lsbit of the private exponent; however that cannot deduce any more than that. I don't believe that the expense of the full test is worth protecting one bit of the exponent. > >> >> On 04/08/2013 02:46 PM, Paul Hoffman wrote: >>> [[ So far, we have received only *one* review of this document, from >>> Tero. If we don't receive more reviews, the document might not >>> progress due to lack of interest. Please review this document within >>> the next week and contribute your review to the list. ]] >>> >>> Greetings. This is the start of the WG Last Call for >>> draft-ietf-ipsecme-dh-checks; the WG period will end in two weeks, on >>> April 15. The current draft is available at >>> http://tools.ietf.org/html/draft-ietf-ipsecme-dh-checks-01 >>> >>> Given that this will be a Standards Track document, it is important for it to >> be reviewed by as many people as possible. Possible results of individual >> reviewing the document are: >>> >>> - "Looks fine, please publish" >>> >>> - "Looks fine, here are some comments" >>> >>> - "Has some problems, here they are" >>> >>> - Other things of that sort >>> >>> Many people on this mailing list are IPsec implementers but are mostly or >> completely silent on the mailing list. If you are one of those people, doing a >> WG Last Call review is a good way to participate usefully in the WG. Please >> strongly consider (a) reading the current draft and (b) sending a message to >> the list with your short or long review. If there are too few reviews on this >> document, we could get pushback from the IESG about the document. >>> >>> --Paul Hoffman >>> _______________________________________________ >>> IPsec mailing list >>> IPsec@ietf.org >>> https://www.ietf.org/mailman/listinfo/ipsec >>> >>> _______________________________________________ >>> IPsec mailing list >>> IPsec@ietf.org >>> https://www.ietf.org/mailman/listinfo/ipsec >>> >> >> _______________________________________________ >> IPsec mailing list >> IPsec@ietf.org >> https://www.ietf.org/mailman/listinfo/ipsec
- [IPsec] NUDGE: WG Last Call for draft-ietf-ipsecm… Paul Hoffman
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Dan Brown
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Andrey Jivsov
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Scott Fluhrer (sfluhrer)
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Andrey Jivsov
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Michael Richardson
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Scott Fluhrer (sfluhrer)
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Tero Kivinen
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Michael Richardson
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Dan Brown
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Michael Richardson
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Yoav Nir
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Andrey Jivsov
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Dan Brown
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Scott Fluhrer (sfluhrer)
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Dan Harkins
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Johannes Merkle
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Paul Hoffman
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Paul Hoffman
- Re: [IPsec] NUDGE: WG Last Call for draft-ietf-ip… Michael Richardson