Re: [TLS] Security review of TLS1.3 0-RTT

Nico Williams <nico@cryptonector.com> Thu, 04 May 2017 20:11 UTC

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Date: Thu, 04 May 2017 15:11:52 -0500
From: Nico Williams <nico@cryptonector.com>
To: Ilari Liusvaara <ilariliusvaara@welho.com>
Cc: Erik Nygren <erik+ietf@nygren.org>, "tls@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] Security review of TLS1.3 0-RTT
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On Thu, May 04, 2017 at 11:01:02PM +0300, Ilari Liusvaara wrote:
> On Thu, May 04, 2017 at 03:12:41PM -0400, Erik Nygren wrote:
> > On Wed, May 3, 2017 at 11:13 PM, Eric Rescorla <ekr@rtfm.com> wrote:
> > > 1. A SHOULD-level requirement for server-side 0-RTT defense, explaining
> > > both session-cache and strike register styles and the merits of each.
> 
> > Many of the discussions I've been in seem to have concluded that we should
> > always be assuming that 0-RTT data can and will be replayed, and
> > applications and application protocols need to design and use it
> > carefully, accordingly.
> 
> The problem is, the amount of replays is so great even non-idempotency
> that is normally of no consequence becomes a major problem. It isn't one
> or two or three replays, it could be _millions_ of replays.

Adaptive fallback to full handshakes.

> Almost nothing is idempotent enough, unless extremely carefully designed,
> and very few things are.

GETs of static data are.

> There are loads of GET endpoints there that don't have any wild non-
> idempotent behaviour, but still aren't idempotent enough.

Yes, this is true.  But the idea is that one should not enable 0-rtt for
servers that have such behavior.

Nico
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