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Re: [Unbearable] 0-RTT Token Binding: When to switch exporters?

Andrei Popov <Andrei.Popov@microsoft.com> Tue, 21 March 2017 17:07 UTC

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From: Andrei Popov <Andrei.Popov@microsoft.com>
To: Eric Rescorla <ekr@rtfm.com>, Martin Thomson <martin.thomson@gmail.com>
CC: Nick Harper <nharper@google.com>, IETF Tokbind WG <unbearable@ietf.org>
Thread-Topic: [Unbearable] 0-RTT Token Binding: When to switch exporters?
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Archived-At: <https://mailarchive.ietf.org/arch/msg/unbearable/t_ItOqvbqjKGo_AZ4LGdJL_DdDs>
Subject: Re: [Unbearable] 0-RTT Token Binding: When to switch exporters?
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The rules for the switch from 0-RTT EKM to the proper EKM are becoming fairly complex and hard-to-enforce.
On the other hand, the use of 0-RTT EKM, generally, makes bound tokens replayable.

I think that a server that cares enough about token replay to enable TB (and verify extra signatures) should not accept 0-RTT (at least with those clients that offer TB).

Cheers,

Andrei

From: Eric Rescorla [mailto:ekr@rtfm.com]
Sent: Tuesday, March 21, 2017 5:24 AM
To: Martin Thomson <martin.thomson@gmail.com>
Cc: Nick Harper <nharper@google.com>; Andrei Popov <Andrei.Popov@microsoft.com>; IETF Tokbind WG <unbearable@ietf.org>
Subject: Re: [Unbearable] 0-RTT Token Binding: When to switch exporters?



On Mon, Mar 20, 2017 at 7:23 PM, Martin Thomson <martin.thomson@gmail.com<mailto:martin.thomson@gmail.com>> wrote:
On 21 March 2017 at 10:32, Nick Harper <nharper@google.com<mailto:nharper@google.com>> wrote:
> All HTTP requests which the client starts processing to send after the
> client sends its Finished message MUST use the exporter_secret for
> their token bindings.

How would a server verify this?

I don't believe it can. It can verify some violations (effectively those that Nick's
role detected) at the HTTP layer.

-Ekr

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