Re: [Cfrg] I-D Action: draft-irtf-cfrg-hpke-02.txt

Michael Scott <mike.scott@miracl.com> Wed, 04 December 2019 11:28 UTC

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From: Michael Scott <mike.scott@miracl.com>
Date: Wed, 4 Dec 2019 11:29:53 +0000
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Subject: Re: [Cfrg] I-D Action: draft-irtf-cfrg-hpke-02.txt
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Hello,

We have implemented an experimental version of HPKE, working from the
latest draft (in the C++ language only for now)

https://github.com/miracl/core

Our experimental API supports all 4 modes of operation, but currently only
for AES-GCM and the curves X25519 and P521.

Some feed-back: It would be a good idea to explicitly warn the reader that
the X25519/X448 keys are actually in little-endian format, whereas for
P256/521 they are big-endian.

The Npk sizes given for the KEMS for curves P256 and P521 appear to be for
a compressed form of the points. In the test vectors uncompressed public
keys are used.

The first test vector provided (for mode 3) appears out-of-order.

Other than that a well written and easy to follow draft.


Mike

On Wed, Dec 4, 2019 at 1:17 AM Nasrul Zikri <nasrulzikri@outlook.com> wrote:

>
> Hello Richard,
>
> Thanks for looking at my use-case. I have been working recently on a quick
> implementation of FFDH so I would be interested to see how this perform in
> HPKE. If I can test this first and then request code points later that is
> good enough. If you can find a way to re-use TLS cipher suite code points
> (like Stephen say) that is good also because this defines
> ffdhe2048(0x0100), ffdhe3072(0x0101), ffdhe4096(0x0102), ffdhe6144(0x0103),
> ffdhe8192(0x0104), ffdhe_private_use(0x01FC..0x01FF).
>
> I think there are improvements that can be made for generating custom
> group for better security and speed. Using custom group help defend against
> an powerful adversary who would put a lot of work into breaking a fixed
> group, so I disagree that they are "even worse idea", but I realise there
> will be difficulties in negotiate parameters for custom group so I don't
> want to delay your draft.
>
> Tk,
> Nasrul
>
>
> ------------------------------
> *From:* Richard Barnes <rlb@ipv.sx>
> *Sent:* Thursday, November 28, 2019 04:02
> *To:* Nasrul Zikri <nasrulzikri@outlook.com>
> *Cc:* cfrg@irtf.org <cfrg@irtf.org>
> *Subject:* Re: [Cfrg] I-D Action: draft-irtf-cfrg-hpke-02.txt
>
> Hi Nasrul,
>
> Thanks for taking a look at this draft.  Personally, I am disinclined to
> define FFDH schemes, unless there are other folks in the RG who think they
> would be useful.  That said, the registry policy on group IDs is
> Specification Required, so you can get code points if you have a
> specification; it doesn't have to be in this doc..  AFAIK, there should be
> no technical barrier to doing FFDH.
>
> As far as custom parameters, I think the only reasonable way to
> accommodate them here would be to reserve some space in the registry for
> private, vendor-specific use.  But this seems like an even worse idea than
> FFDH, so again, I'm inclined to do nothing here.
>
> If other folks are interested in these cases, please speak up.
>
> --Richard
>
>
> On Wed, Nov 20, 2019 at 1:32 AM Nasrul Zikri <nasrulzikri@outlook.com>
> wrote:
>
> On your draft of Hybrid Public Key Encryption.
>
> The draft appears to be for any DH KEM, but I note, however that the
> examples and test vectors it gives are only for the elliptic curves
> P-256, Curve25519, P-521, Curve448.
>
> Would it be possible to define the algorithm identifiers and test
> vectors for some FFDH groups as well as the elliptic curve? Or is there
> some important reason why only ECDH methods are suitable?
>
> If FFDH groups are indeed correct for use in the draft, it would appear
> that the table in section 8.1 could be extended to allocate identifiers
> for at least the parameter ffdhe2048, ffdhe3072, ffdhe4096, ffdhe6144,
> ffdhe8192 as stated in RFC 7919, and perhaps the MODP groups as stated
> in RFC 3526 and RFC 5114.
>
> I would also like there to be a way of specifying the use of a custom
> finite field for when the use of a defined elliptic curve or finite
> field is not enough. I realise that stating a method for transporting
> the parameters {p,q,g} is outside the scope of this draft, but could a
> value for custom groups or private use be stated in this table also?
>
> Tk,
> Nasrul
>
>
>
> > Hey all,
> >
> > Happy IETF 106 deadline day!
> >
> > The authors feel that this version of HPKE is substantially complete.
> All
> > of the functional parts are there, as well as test vectors to facilitate
> > interop.  And I think we've got some formal proofs on the way.  Please
> take
> > a look and speak up if you see any gaps.
> >
> > Thanks,
> > --Richard
> >
> > On Mon, Nov 4, 2019 at 3:47 PM <internet-drafts@ietf.org>rg>; wrote:
> >
> > >
> > > A New Internet-Draft is available from the on-line Internet-Drafts
> > > directories.
> > > This draft is a work item of the Crypto Forum RG of the IRTF.
> > >
> > >         Title           : Hybrid Public Key Encryption
> > >         Authors         : Richard L. Barnes
> > >                           Karthik Bhargavan
> > >         Filename        : draft-irtf-cfrg-hpke-02.txt
> > >         Pages           : 45
> > >         Date            : 2019-11-04
> > >
> > > Abstract:
> > >    This document describes a scheme for hybrid public-key encryption
> > >    (HPKE).  This scheme provides authenticated public key encryption of
> > >    arbitrary-sized plaintexts for a recipient public key.  HPKE works
> > >    for any combination of an asymmetric key encapsulation mechanism
> > >    (KEM), key derivation function (KDF), and authenticated encryption
> > >    with additional data (AEAD) encryption function...  We provide
> > >    instantiations of the scheme using widely-used and efficient
> > >    primitives.
> > >
> > >
> > > The IETF datatracker status page for this draft is:
> > > https://datatracker.ietf.org/doc/draft-irtf-cfrg-hpke/
> > >
> > > There are also htmlized versions available at:
> > > https://tools.ietf.org/html/draft-irtf-cfrg-hpke-02
> > > https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-hpke-02
> > >
> > > A diff from the previous version is available at:
> > > https://www.ietf.org/rfcdiff?url2=draft-irtf-cfrg-hpke-02
> > >
> > >
> > > Please note that it may take a couple of minutes from the time of
> > > submission
> > > until the htmlized version and diff are available at tools.ietf.org.
> > >
> > > Internet-Drafts are also available by anonymous FTP at:
> > > ftp://ftp.ietf.org/internet-drafts/
> > >
> > > _______________________________________________
> > > Cfrg mailing list
> > > Cfrg@irtf.org
> > > https://www.irtf.org/mailman/listinfo/cfrg
>
>
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