Re: [TLS] Forward secrecy with resumption, and 0-RTT security

Tony Arcieri <bascule@gmail.com> Sun, 06 December 2015 23:00 UTC

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From: Tony Arcieri <bascule@gmail.com>
Date: Sun, 6 Dec 2015 15:00:23 -0800
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To: Bill Cox <waywardgeek@google.com>
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Subject: Re: [TLS] Forward secrecy with resumption, and 0-RTT security
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On Sun, Dec 6, 2015 at 6:50 AM, Bill Cox <waywardgeek@google.com> wrote:

> In the past, there were two cases: resumption using session IDs, and
> resumption with session tickets.  Using session IDs loses forward secrecy,
> because the server always has session keys in a session cache, which could
> be used to decrypt the prior sessions.  Using tickets did not work either,
> because the server always kept a ticket decryption key which could be used
> to decrypt all resumed sessions since the key was last rotated.
>
> My first question is: Do we care?
>

At least for session tickets, I don't care. There's a simple enough way to
solve that problem: rotate the session ticket key every few days.

-- 
Tony Arcieri