Re: [TLS] A closer look at ROBOT, BB Attacks, timing attacks in general, and what we can do in TLS

Eric Rescorla <ekr@rtfm.com> Fri, 15 December 2017 18:08 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Fri, 15 Dec 2017 10:07:16 -0800
Message-ID: <CABcZeBOsL0a0xHvVWEus_EY3mUNioaV9fsz89Gt+HeqdHpoyDw@mail.gmail.com>
To: Ilari Liusvaara <ilariliusvaara@welho.com>
Cc: Andrei Popov <Andrei.Popov@microsoft.com>, "tls@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] A closer look at ROBOT, BB Attacks, timing attacks in general, and what we can do in TLS
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I'm not quite following how this helps. It's true that if SHA-256 is
broken, we're in serious trouble, but that's largely because of the fact
that that's what people's certificates have, so clients really can't refuse
to support SHA-256 certificates. So, how does adding new algorithms help?
(That's why I would argue that the existing SHA-384 support doesn't help).

-Ekr


On Fri, Dec 15, 2017 at 9:46 AM, Ilari Liusvaara <ilariliusvaara@welho.com>;
wrote:

> On Fri, Dec 15, 2017 at 02:57:33PM +0000, Andrei Popov wrote:
> > From: TLS [mailto:tls-bounces@ietf.org] On Behalf Of Ilari Liusvaara
> > > Even nastier dependency: SHA-2. If that breaks, currently both TLS
> > > 1.2 and 1.3 break. There are no alternatives defined.
> >
> > Here's an attempt to define a SHA-2 alternative:
> https://tools.ietf.org/html/draft-wconner-blake2sigs-01
>
> Also would need TLS ciphersuite codepoints with alternative handshake
> hash algorithms.
>
>
> -Ilari
>
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