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Re: [tcpinc] Eric Rescorla's Discuss on draft-ietf-tcpinc-tcpeno-13: (with DISCUSS and COMMENT)

Eric Rescorla <ekr@rtfm.com> Sun, 12 November 2017 07:22 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Sun, 12 Nov 2017 07:21:42 +0000
Message-ID: <CABcZeBO0TD0KnpTfe6CbHUoiS=FmGiGW6r_mFMH_9bYFWKqKLA@mail.gmail.com>
To: Kyle Rose <krose@krose.org>
Cc: "Black, David" <David.Black@dell.com>, The IESG <iesg@ietf.org>, "draft-ietf-tcpinc-tcpeno@ietf.org" <draft-ietf-tcpinc-tcpeno@ietf.org>, "tcpinc-chairs@ietf.org" <tcpinc-chairs@ietf.org>, "tcpinc@ietf.org" <tcpinc@ietf.org>
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Subject: Re: [tcpinc] Eric Rescorla's Discuss on draft-ietf-tcpinc-tcpeno-13: (with DISCUSS and COMMENT)
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On Sun, Nov 12, 2017 at 7:19 AM, Kyle Rose <krose@krose.org> wrote:

> On Sun, Nov 12, 2017 at 1:13 PM, Eric Rescorla <ekr@rtfm.com> wrote:
> > On Sun, Nov 12, 2017 at 5:08 AM, Black, David <David.Black@dell.com>
> wrote:
> >> - Encryption: The intent is - don't use anything weaker than AES-128,
> >> e.g., don't even think about using 3DES.  The concern is how to write
> that
> >> requirement in a way that would survive hypothetical discovery of a
> >> catastrophic cryptanalytic attack on AES-128.
> >
> >
> > Or even a small one. I mean, what does this say about Curve25519 or 4Q.
>
> I think this is actually the issue driving the vagueness of the
> requirement: e.g., if some hypothetical attack against AES-128 reduced
> security by a few bits. The intent, as David suggests, is to prohibit
> the use of something like DES, not to prohibit a 128-bit cipher with
> only (say) 125 bits of security.
>

That's not a reasonable desire, but this is an RFC 2119 requirement, so it
really does need to be unambiguous.

-Ekr

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