Re: [TLS] Closing on 0-RTT

Benjamin Kaduk <bkaduk@akamai.com> Thu, 06 July 2017 19:10 UTC

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From: Benjamin Kaduk <bkaduk@akamai.com>
To: Eric Rescorla <ekr@rtfm.com>, "tls@ietf.org" <tls@ietf.org>
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Date: Thu, 06 Jul 2017 14:10:16 -0500
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Subject: Re: [TLS] Closing on 0-RTT
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On 06/30/2017 11:32 AM, Benjamin Kaduk wrote:
> On 06/29/2017 03:53 PM, Eric Rescorla wrote:
>> I have updated the PR to match people's comments. I would like to
>> merge this soon, so please get any final comments in.
>
> I made a couple comments on the PR that are more appropriate for the
> list, so I'll repeat them here and hopefully get replies from the
> broader audience.
>
>
> First off, I think we should MUST-level require servers to implement a
> hard limit on the number of replays accepted.  However, it doesn't
> quite seem realistic to require "MUST use either [single-use tickets]
> or [ClientHello recording]".  My preference would be "MUST use either
> [single-use tickets], [ClientHello recording], or equivalently strong
> protection", but I don't know what level of support we have for such a
> strong requirement.  As an alternative, I will also put out "MUST
> limit replays to at most the number of endpoints capable of accepting
> connections for a given identity, and SHOULD provide even stronger
> replay protections, such as [single-use tickets] or [ClientHello
> recording]."  I think we have general agreement that strong
> anti-replay as described in the document is feasible for a
> single-server deployment, and this last formulation is achievable in
> multi-server environments by just giving each server its own local
> per-server protection.  (My main reason for wanting a MUST-level hard
> cap is that I worry that millions/billions of replays will have really
> nasty consequences in terms of DoS and side channel issues.)
>
> But, this has been quite a long thread spread out over multiple
> forums/email subjects, so I've also probably forgotten some of the
> arguments presented against having MUST-level strong anti-replay
> requirements; I'd greatly appreciate if someone could repeat them here
> for everyone's consideration.

Or are there no such arguments?
The only one I remember is the implementation complexity for distributed
systems, but if you can implement for a single-node system my compromise
proposal is trivially implementable.

-Ben