Re: [TLS] Relative vs absolute ServerConfiguration.expiration_date

Eric Rescorla <ekr@rtfm.com> Wed, 22 July 2015 20:01 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Wed, 22 Jul 2015 21:59:20 +0200
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To: Blake Matheny <bmatheny@fb.com>
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Subject: Re: [TLS] Relative vs absolute ServerConfiguration.expiration_date
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On Wed, Jul 22, 2015 at 9:55 PM, Blake Matheny <bmatheny@fb.com> wrote:

> One of the topics of discussion at the WG discussion was whether
> ServerConfiguration.expiration_date should be an absolute or relative
> value. Subodh (CC) dug into our production data and found that nearly half
> of the TLS errors we see in production (end user to edge/origin) are due to
> date mismatch. This often occurs when people intentionally reset the clock
> on their phone, or for other various reasons.
>
> Due to the high rate of date mismatch errors we see, my preference would
> be that ServerConfiguration.expiration_date be a relative value instead of
> an absolute one. This provides the client an opportunity to correctly use a
> monotonic (or other similar) clock to minimizing exposure, without losing
> the value of the ServerConfiguration. Using an absolute value means that
> ServerConfiguration, for clients with invalid clocks, would essentially
> never be cacheable. These clients wouldn’t benefit from ServerConfiguration.
>
> Thoughts or feedback?


Can you provide a sense of the range of clock skew you are seeing? I'm
trying to
figure out how many of these clients are going to start choking with OCSP
must-staple, short-lived certs, etc.

-Ekr