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Re: [TLS] Unifying tickets and sessions

Stephen Checkoway <s@pahtak.org> Thu, 23 October 2014 19:36 UTC

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From: Stephen Checkoway <s@pahtak.org>
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Subject: Re: [TLS] Unifying tickets and sessions
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On Oct 23, 2014, at 2:36 PM, Viktor Dukhovni <ietf-dane@dukhovni.org> wrote:

> The number of key sets is irrelevant, all that matters is how long
> each one is retained.  Postfix defaults to 2 hours (1 hour encrypt
> and 1 hour decrypt).  With N keysets, you'd have (T encrypt, (N-1)*T
> decrypt).

This seems perfectly reasonable (both for general N and for specific N = 2 or N = 3). But does it make any difference from a protocol perspective? The only way a client could tell if a server is doing something wrong is if the client knows the upper limit on the ticket's validity  NT and sends a ticket after that time which the server accepts.

I'm probably missing something but it seems like there's no real way to detect if the server has followed any particular policy for a ticket so the details (such as key rotation and symmetric algorithm strength) should be left entirely up to the server. (Or resumption should be dropped from 1.3.)

Giving guidance seems reasonable. Setting unenforceable limits does not.

-- 
Stephen Checkoway

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