Re: [Cfrg] Adoption call for draft-barnes-cfrg-hpke
Richard Barnes <rlb@ipv.sx> Sat, 27 April 2019 21:24 UTC
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From: Richard Barnes <rlb@ipv.sx>
Date: Sat, 27 Apr 2019 17:23:43 -0400
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To: Dan Brown <danibrown@blackberry.com>
Cc: Paterson Kenneth <kenny.paterson@inf.ethz.ch>, "cfrg@irtf.org" <cfrg@irtf.org>
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Subject: Re: [Cfrg] Adoption call for draft-barnes-cfrg-hpke
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Hi Dan, Thanks for the comments. A couple of replies inline below. On Fri, Apr 26, 2019 at 12:58 PM Dan Brown <danibrown@blackberry.com> wrote: > > > -----Original Message (abbreviated) ----- > > From: Cfrg <cfrg-bounces@irtf.org> On Behalf Of Paterson Kenneth > > Sent: Friday, April 26, 2019 4:09 AM > > This email starts a 2-week adoption call for: > > > > Hybrid Public Key Encryption > > > > Please give your views on whether this document should be adopted as a > CFRG > > draft, and if so, whether you'd be willing to help work on it/review it. > > I think it item should be adopted, with changes, though I'm not sure how > much I will be able to work on it or review it. > > Minor comments: > > The word "hybrid" now has 3 distinct meanings in crypto, two of them nearly > opposite. The older meaning refers a system, with security relying on both > components of the hybrid, i.e. weakest link. This is what HPKE means: > both > ECDH and AES-GCM must be secure, for example. A newer, nearly opposite, > meaning is defense-in-depth, redundancy, strongest-link, etc., for example > ECC+PQC. (A third meaning refers to a type of security proof.) Based on > its title, this document could be expected to be a how-to on combining > ECC+PQC+RSA+... (Arguably, the older meaning of "hybrid" should have > precedence, and the newer meaning is infringing, etc.) I recommend > changing > "hybrid" to something else, but suffer from writer's block for an > alternative (sorry). > Yeah, Karthik and I spent a fair bit of time brainstorming alternatives, and didn't come up with anything better. FWIW, my personal favorite among what we invented was Combined Asymmetric / Symmetric Hybrid Encryption Wrapping, or CASHEW. > A well-known downside of ECIES (and any PKE) is the lack of forward secrecy > (on the recipient side). In the olden times of ECC versus RSA, a real risk > was somebody drop-in replacing RSA by ECIES, even when some type of > forward-secure ECDH was possible. The famous example TLS 1.3 of requiring > (EC)DHE should now minimize this risk. Nonetheless, a PKE document is > better > if it (somehow?) recommends the reader to use forward security if possible. > (Maybe current draft does this well enough already.) > I would be be open to suggestions here if you have more concrete thoughts. My main worry going down this line is that I don't think we want to invent too much protocol here, vs. keeping this to a fairly small, reusable tool. Given that forward secrecy typically involves a lot of context and RTTs, it might be better to punt and say, "You should aim for forward secrecy, and for that you need more of a full protocol, e.g., MLS". After all, the whole point of MLS is arguably to build up from HPKE to something with forward secrecy and post-compromise security. > Perhaps differences in HPKE from ECIES standards (i.e. algorithm, security, > efficiency) - especially if those ECIES standards were implemented - should > be documented (in an tedious appendix or table)? Also what about a > comparison to other types of ECPKE: Cramer--Shoup encryption, NaCL's > crypto_box, even ECC-in-CMS EnvelopedData, etc? > Good idea. I've filed an issue in our repo. > An updated link of SEC1 v2 for is http://www.secg.org/sec1-v2.pdf (Sorry > that PDF metadata title is version 1.9.) The ECIES in SEC1 v2 is rather > outdated in its symmetric component (i.e. AEAD part). It uses a menu of > KDF, XOR/AES/DES CTR/CBC, HMAC/CMAC, and then some concatenation of 2 extra > info inputs. (Perhaps, one day a new version SEC1 will correct/modernize > this, though CFRG may not care.) > > The ANSI X9.63-2011 standard used the extended KDF output as XOR key > stream, > and then an "Approved MAC", which allows HMAC, but also allows updates via > other X9 documents, mainly the registry, (pointing to NIST MACs). > > There was an aim that the intersection of the ECIES versions defined IEEE > 1363a, SEC1 and X9.63 was non-empty. Not sure if HPKE wants to aim for > similar backwards interop. > Personally, I am not inclined to bother with this. If someone wants to work out what it would take to achieve this and propose a solution, I would be willing to review a proposal. --Richard > > > > _______________________________________________ > Cfrg mailing list > Cfrg@irtf.org > https://www.irtf.org/mailman/listinfo/cfrg >
- [Cfrg] Adoption call for draft-barnes-cfrg-hpke Paterson Kenneth
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Stanislav V. Smyshlyaev
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Stephen Farrell
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Richard Barnes
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Benjamin Beurdouche
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Scott Arciszewski
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Dan Brown
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Mehmet Adalier
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Russ Housley
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… denis bider
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… John Mattsson
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Christopher Wood
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Richard Barnes
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Richard Barnes
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Paul Lambert
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… mcgrew
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Marek Jankowski
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Jim Schaad
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Hugo Krawczyk
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Dan Brown
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Hugo Krawczyk
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Natanael
- Re: [Cfrg] Adoption call for draft-barnes-cfrg-hp… Alexey Melnikov