[TLS] [PSA] 0-RTT tolerance is mandatory

Hubert Kario <hkario@redhat.com> Wed, 04 July 2018 12:42 UTC

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From: Hubert Kario <hkario@redhat.com>
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Date: Wed, 04 Jul 2018 14:42:51 +0200
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Subject: [TLS] [PSA] 0-RTT tolerance is mandatory
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All the implementations I deal with in my day-to-day work fail to handle the 
0-RTT client hello correctly when the 0-RTT support is not enabled on the 

I.e. they ignore the MUST clause from
https://tools.ietf.org/html/draft-ietf-tls-tls13-28#page-58 stating that the 
server can handle an early_data extension (and following encrypted data) in 
only one of three ways, neither which allows for unconditional connection 

This also runs afoul the recommendation from https://tools.ietf.org/html/
draft-ietf-tls-tls13-28#section-D.3 on 0-RTT backwards compatibility.

Quick test can be performed by running the tlsfuzzer script.
Start a server on port 4433 (or use the -p switch to the test case to change 
it) on localhost (or use -h switch to provide ip or hostname) with support for 
draft-28, a RSA server key, support for P-256 ECDH, AES-128-GCM cipher and 
SHA-256 signature hash. The server needs to be able to respond to a record 
with an HTTP GET query (i.e. either HTTP server or an echo server will work).

Download the requirements:
git clone https://github.com/tomato42/tlsfuzzer
pushd tlsfuzzer
# won't be needed after tlsfuzzer#423 PR is merged
git checkout 0rtt-garbage-resumption
git clone https://github.com/tomato42/tlslite-ng .tlslite-ng
ln -s .tlslite-ng/tlslite tlslite
git clone https://github.com/warner/python-ecdsa .python-ecdsa
ln -s .python-ecdsa/ecdsa ecdsa

Run the test case:
PYTHONPATH=. python scripts/test-tls13-0rtt-garbage.py

successful run will print
Test end
successful: 3
failed: 0

at the end

the test case supports also --num-bytes switch to provide how big the early 
data should be (sends 2^14B by default).
Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purky┼łova 115, 612 00  Brno, Czech Republic