Re: [TLS] Further TLS 1.3 deployment updates

Hubert Kario <hkario@redhat.com> Thu, 13 December 2018 16:54 UTC

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From: Hubert Kario <hkario@redhat.com>
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Date: Thu, 13 Dec 2018 17:53:51 +0100
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Subject: Re: [TLS] Further TLS 1.3 deployment updates
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On Wednesday, 12 December 2018 23:21:43 CET David Benjamin wrote:
> Hi folks,
> 
> We have one more update for you all on TLS 1.3 deployment issues. Over the
> course of deploying TLS 1.3 to Google servers, we found that JDK 11
> unfortunately implemented TLS 1.3 incorrectly. On resumption, it fails to
> send the SNI extension. This means that the first connection from a JDK 11
> client will work, but subsequent ones fail.
> https://bugs.openjdk.java.net/browse/JDK-8211806
> 
> It appears this will be fixed in JDK 11.0.2, which is not yet released. In
> the meantime, we have sadly had to detect JDK 11 clients and disable TLS
> 1.3 for them. This, in turn, raises a problem with the downgrade signal in
> ServerHello.random. JDK 11 does implement that downgrade signal, so the
> workaround cannot send it. However, the signal is not effective for other
> clients unless all TLS 1.2 ServerHellos are marked.
> 
> To salvage this for now, we've introduced a second value, generated
> randomly:
>     0xed, 0xbf, 0xb4, 0xa8, 0xc2, 0x47, 0x10, 0xff
> 
> When Google servers detect JDK 11 and disable TLS 1.3 to work around this
> issue, they will use that value in ServerHello.random instead of the
> standard 0x44, 0x4f, 0x57, 0x4e, 0x47, 0x52, 0x44, 0x01. Future versions of
> Chrome will treat the new value as an alias of the standard one. Other
> clients may wish to do the same, but please properly test your TLS 1.3
> implementation first.

there is now a server test script in tlsfuzzer for standard downgrade 
sentinel:
https://github.com/tomato42/tlsfuzzer/blob/master/scripts/test-downgrade-protection.py

example of usage: https://github.com/tomato42/tlsfuzzer/pull/479/files

-- 
Regards,
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