Re: [TLS] Should we support static RSA in TLS 1.3?

Eric Rescorla <ekr@rtfm.com> Sun, 17 November 2013 05:27 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Sat, 16 Nov 2013 21:26:34 -0800
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To: Watson Ladd <watsonbladd@gmail.com>
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Subject: Re: [TLS] Should we support static RSA in TLS 1.3?
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On Sat, Nov 16, 2013 at 9:13 PM, Watson Ladd <watsonbladd@gmail.com> wrote:

> On Sat, Nov 16, 2013 at 9:03 PM, Eric Rescorla <ekr@rtfm.com> wrote:
>  > That said, using ephemeral keying doesn't really improve latency
> > that much. There are a number of cases to consider, but off the top
> > of my head you get between 0-1/2 RTT by switching to ephemeral
> > exchange, depending on how much information the client has
> > about the server.
> If you use a signature, rather than an encrypted message, you get
> three passes rather than four, and can send
> arbitrary client data in the third pass that is authenticated and
> encrypted. This is effectively a 1-RT protocol if
> the client goes first in the application layer.


I'll revise what I said to 0-1RTT improvement. With that said...

- This depends on the client being able to send their share in the
first message, which requires some foreknowledge of what
parameters are acceptable.

- On repeated exchanges, the client can cache the server's
cert (Fast Track) and we're back to 1 RT.

- TLS with False Start is already 1RT, albeit without the client
being able to verify handshake correctness until he sees the
server's response.

-Ekr