Re: [TLS] 2nd WGLC: draft-ietf-tls-tls13

Eric Rescorla <> Tue, 11 July 2017 20:51 UTC

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From: Eric Rescorla <>
Date: Tue, 11 Jul 2017 13:50:48 -0700
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To: Benjamin Kaduk <>
Cc: Sean Turner <>, "<>" <>
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Subject: Re: [TLS] 2nd WGLC: draft-ietf-tls-tls13
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On Tue, Jul 11, 2017 at 1:39 PM, Benjamin Kaduk <>; wrote:
> Another question I also relates to 0-RTT, specifically with the freshness
> checks and the case where the computed expected_arrival_time is in outside
> "the window" by virtue of being in the future. (See the Note: at the end of
> section 8.2.) (The case where the expected_arrival_time is in the past can
> clearly be treated as "this is a stale request" and the current text about
> aborting with "illegal_parameter" or rejecting 0-RTT but accepting the PSK
> is acceptable, even if it doesn't give guidance as to what might cause
> someone to pick one behavior or the other.)  I am wondering whether we
> should consider this to be a potential attack and abort the connection.  I
> concede that there are likely to be cases where this
> situation occurs incidentally, for clients with extremely fast-running
> clocks, and potential timezone/suspend-resume weirdness.  But there is also
> the potential for a client that deliberately lies about its ticket age and
> intends to replay the wire messages when the age becomes in window, or an
> attacker that records the messages and knows that the client's clock is too
> fast, or other cases.  (A client that deliberately does this could of
> course just send the same application data later as well.)  If the time is
> only a few seconds out of the window, then delaying a response until it is
> in the window and only then entering it into the single-use cache might be
> reasonable, but if the time is very far in the future, do we really want to
> try to succeed in that case?

If the time is very far in the future, the text is supposed to tell you to
fall back
to 1-RTT...

It looks like we no longer do anything to obsolete/reserve/similar the
> HashAlgorithm and SignatureAlgorithm registries; was that just an editorial
> mixup or an intended change?

We removed the API guidance for separate APIs for read/writing early data
> versus regular data, which I believe had consensus.  But I thought we were
> going to say something carefully worded about having an API to determine
> whether the handshake has completed (or client Finished has been validated,
> or ...), and it looks like this is buried at the end of E.5(.0), with the
> string "API" not appearing.  It might be useful to make this a little more
> prominent/discoverable, whether by subsection heading or otherwise.

Suggestions welcome for where this would be better....


> I also found some issues that I believe to be purely editorial, for which
> I will submit a pull request.
> I will probably try to make another full review pass over the entire
> document (mostly looking for editorial things), but I have until the end of
> IETF LC for that, right? ;)
> -Ben
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