[TLS] 0-RTT encrypted data limits

Hubert Kario <hkario@redhat.com> Wed, 31 August 2016 18:14 UTC

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From: Hubert Kario <hkario@redhat.com>
To: tls@ietf.org
Date: Wed, 31 Aug 2016 20:14:33 +0200
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Subject: [TLS] 0-RTT encrypted data limits
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Current draft has the following text in it:

    If any of these checks fail, the server MUST NOT respond
    with the extension and must discard all the remaining first
    flight data (thus falling back to 1-RTT). If the client attempts
    a 0-RTT handshake but the server rejects it, it will generally
    not have the 0-RTT record protection keys and must instead
    trial decrypt each record with the 1-RTT handshake keys
    until it finds one that decrypts properly, and then pick up
    the handshake from that point.

My understanding of that, in case client does 0-RTT but server rejects it 
(because the PSK is too old or its time is different enough) is that the 
server needs to keep on reading arbitrarily large amounts of data it has no 
idea what to do with. All using slow path (thinking exception handling in 

Is my understanding correct?

Why is there no limit on the amount of data that can be encrypted using PSK 
keys (0-RTT)?
Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purky┼łova 99/71, 612 45, Brno, Czech Republic