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Re: [TLS] Server time

Peter Gutmann <pgut001@cs.auckland.ac.nz> Mon, 06 April 2015 11:15 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: "<tls@ietf.org>" <tls@ietf.org>
Thread-Topic: [TLS] Server time
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Date: Mon, 06 Apr 2015 11:15:44 +0000
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Subject: Re: [TLS] Server time
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Dave Garrett <davemgarrett@gmail.com> writes:

>adding a 4 byte uint32 ServerHello.time for TLS 1.3+ seems like a really
>simple solution. (note that ServerHello is already changed by dropping
>compression_method)

It's also a really dangerous solution.  All of PKI is critically dependent on
everyone having the correct time.  For a server to advertise the fact that its
clock is off, and thus revoked and expired certs will still be regarded as
valid (among other things) is a really bad idea.

>The ability of a client to sanity check or sync its time seems like something
>worth having, especially for only a 4 byte cost.

Given that there's already a globally-deployed dedicated infrastructure that
requires nothing more complicated than sending a single UDP packet to port 123
and checking the response, turning your TLS server into a sort of proxy time
server that may or may not have the correct time in the first place seems like
a bad idea.

Peter.

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