Re: [TLS] analysis of wider impact of TLS1.3 replayabe data

Bill Cox <waywardgeek@google.com> Mon, 14 March 2016 19:32 UTC

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Date: Mon, 14 Mar 2016 12:32:50 -0700
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From: Bill Cox <waywardgeek@google.com>
To: =?UTF-8?Q?Colm_MacC=C3=A1rthaigh?= <colm@allcosts.net>
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Subject: Re: [TLS] analysis of wider impact of TLS1.3 replayabe data
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On Mon, Mar 14, 2016 at 9:34 AM, Colm MacCárthaigh <colm@allcosts.net>;
wrote:

>
>
> On Sun, Mar 13, 2016 at 12:04 PM, Bill Cox <waywardgeek@google.com>; wrote:
>>
>> IMO, 0-RTT is the most important new feature in TLS 1.3 ...  Speed really
>> _is_ that important.
>>
>
> I just want to be super explicit on this. There is a trade off to be made
> here between fast and loose Vs security and safety. My take is that speed
> absolutely is not so important that forward-secrecy for user requests, or
> replay safety for applications should be compromised.
>

I agree that the default mode of operation needs to be secure and safe.
Since 0-RTT is so important for TLS 1.3, I would favor making the default
0-RTT mode secure.


> Even better speed benefits can be had by using persistent connections,
> which incidentally are also a little more robust against traffic analysis.
>

Exactly.  Stateful 0-RTT session resumption can get us there, I think.  The
simplest approach I can think of is to use session caches.  If we don't
mind some PFS loss (comparable to what we got in TLS 1.2), the
straight-forward 0-RTT solution seems to work.

Bill