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., Purkyňova 115, 612 00 Brno, Czech Republic
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