Re: ssh-ed25519 implementations

Eric Rescorla <ekr@rtfm.com> Thu, 11 May 2017 05:21 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Wed, 10 May 2017 09:20:37 -0700
Message-ID: <CABcZeBNYUV=-azoZzZjnNtCEu3K0A-THHN2mt02V65oihbbrXw@mail.gmail.com>
Subject: Re: ssh-ed25519 implementations
To: Mark Baushke <mdb@juniper.net>
Cc: "ietf-ssh@NetBSD.org" <ietf-ssh@netbsd.org>, "curdle@ietf.org" <curdle@ietf.org>
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On Wed, May 10, 2017 at 9:18 AM, Mark Baushke <mdb@juniper.net> wrote:

> Hi,
>
> Eric Rescorla <ekr@rtfm.com> has brought to my attention that in
> https://tools.ietf.org/html/draft-ietf-curdle-ssh-curves-04 it is
> currently specifying the SSH encoding of secrets on the wire using the
> mpint process as described in section 5 of [RFC4251] while RFC 7748
> describes using a little-endian format:
>
>   GF(2^448 - 2^224 - 1) and are encoded as an array of bytes, u,
>   in little-endian order such that u[0] + 256*u[1] + 256^2*u[2] + ... +
>
> This seems to be what is being implemeneted for
> curve25519-sha256@libssh.org, so I should make
> an explicit note of this in the draft.
>

Thanks. To be clear, I'm not saying this is the wrong thing in the draft
(though I do think it's kind of an unfortunate outcome). I just think it's
critically important to be clear.


>
> However, I am unaware of any curve448-sha512 implementations at
> present and would like consensus that it should also follow the mpint
> method rather than the RFC 7748 method.
>

I tend to think the 7748 method, but all the options are pretty terrible
here

-Ekr


>
> Please reply to curdle@ietf.org with your opinions.
>
>         Thank you,
>         -- Mark
>
>