Re: [TLS] New Version Notification for draft-bzwu-tls-ecdhe-keyshare-00.txt

" 武炳正(允中) " <bingzheng.wbz@alibaba-inc.com> Tue, 28 April 2015 06:41 UTC

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From: "=?GBK?B?zuSx/tX9KNTK1tAp?=" <bingzheng.wbz@alibaba-inc.com>
To: "'Ilari Liusvaara'" <ilari.liusvaara@elisanet.fi>
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Date: Tue, 28 Apr 2015 14:41:18 +0800
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Subject: Re: [TLS] New Version Notification for draft-bzwu-tls-ecdhe-keyshare-00.txt
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> > Thanks for reminding.
> > Maybe a 'type' should be added in each ClientKeyShareOffer, to indicate
> different Diffie-Hellman exchange.
> > And change this extension's name from ECDHE-keyshare to DH-keyshare.
> 
> Well, there is a draft in pipeline (IETF LC complete, waiting for
> writeup) that assigns a range of group IDs for finite-field Diffie- Hellman (the
> TLS 1.3 group ids come from there).
> 
> Basically, the MSB of group ID being 0x01 means DHE (others are ECDHE).

Thanks again.
I find it in http://datatracker.ietf.org/doc/draft-ietf-tls-negotiated-ff-dhe/ .
So it seems that the 'type' is not need.
I only need to change the extension's name and description.


> > > I consider supporting arbitrary curves here a bad idea. Why not just
> > > use values out of EC Named Curve Registry (16-bit)?
> > >
> > > (That's the way TLS 1.3 does it).
> >
> > I tried to change as less as possible, to avoid unnecessary trouble, both in
> protocol or implementation.
> 
> Well, the difference between ECParameters and NamedCurve when
> non-named groups are disallowed is extra 0x03 prefix (to designate
> NamedCurve).

It's still easier to reuse tls1_check_curve() in OpenSSL if keeping the extra prefix.

> 
> Also, I consider using non-named groups to bring more security problems than
> it is worth (e.g. currently known ways to exploit THS for (EC)DHE rely on those).

This extension aims to reduce the handshake's latency only.
I think it's more clear that this extension behaves the same as normal handshake, both for SSL library's developer and web server administrator.
If someone thinks non-named curve is not safe, he should find a way to disable it for normal handshake;
and this extension will not use non-named curves then.

For example, a web server administrator may prefer the instructions that "non-named curve is not safe. disable it in configure file",
 than " non-named curve is not safe. but there is an extension which disable it automatically. However you still need to disable it in configure file".


expect for your recommendation
Bingzheng Wu