Re: [TLS] What would make TLS cryptographically better for TLS 1.3

Watson Ladd <watsonbladd@gmail.com> Sun, 03 November 2013 23:28 UTC

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Date: Sun, 3 Nov 2013 15:28:14 -0800
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From: Watson Ladd <watsonbladd@gmail.com>
To: Ralf Skyper Kaiser <skyper@thc.org>
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Subject: Re: [TLS] What would make TLS cryptographically better for TLS 1.3
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On Sun, Nov 3, 2013 at 3:23 PM, Ralf Skyper Kaiser <skyper@thc.org> wrote:
> Hi Yoav,
>
> i agree with the UI issue. That's the only use that I can see where
> renegotiation is useful.
>
> I would guess here that 99% of all TLS users (if not 99.99%) do not need
> this feature.
>
> The 99.99% of all users would have to carry the risk of complexity to
> satisfy the need of the 0.01% of users.
>
> There are hopefully other ways to satisfy the need of the 0.01% without the
> 99.99% of us having to take an extra risk (complexity). (Anyone? Ideas are
> welcome...).
Kick it into the application layer.
>
> (ps when i'm speaking about complexity i do not mean the working hours it
> would take to write the code [earlier replies by somebody indicated this]
> but rather the security complexity [making mistakes and auditing a
> process/procedures/... that is rarely used]).
>
> regards,
>
> ralf
>
>
>
>
> On Sun, Nov 3, 2013 at 7:18 PM, Yoav Nir <ynir@checkpoint.com> wrote:
>>
>>
>> On Nov 3, 2013, at 9:03 AM, Ralf Skyper Kaiser <skyper@thc.org> wrote:
>>
>> > Hi,
>> >
>> > avoid renegotiation. It serves no purpose and only adds complexity. It
>> > is so much more secure to kill and re-establish the TLS if the counters run
>> > out instead of renegotiating.
>> >
>>
>> Hi, Ralf
>>
>> The one use of renegotiation that I'm aware of, is for overcoming a UI
>> issue in browsers. If you do a TLS handshake with mutual authentication (so
>> the server sends a CertReq), the browser pops up a dialog box with all the
>> certificates you might have. Website designers with to avoid that,
>> especially on the welcome screen, so the web server does not send a CertReq.
>> Instead, they present a welcome screen with a button or link that says
>> "Login with certificates" Clicking that performs a regular SSL handshake (or
>> does nothing at all if the connection is already established), but when the
>> request comes in ("GET /login_with_certs HTTP/1.1"), the web server sends a
>> HELLO_REQUEST, and in the resulting handshake it sends the CertReq, so the
>> pop-up appears when the user *is* expecting it.
>>
>> I totally agree that renegotiation for rekeying is useless for people who
>> are not doing DES-CBC and 3DES-CBC. It's even superfluous for them in most
>> cases (you're pretty save doing 500,000,000 blocks, and that's 4 GB in 3DES.
>> How many sites do you browse with 4 GB?  Maybe downloading stuff…)
>>
>> But before we can drop renegotiation from the standards, or recommend that
>> implementors don't implement it, we need an alternate mechanism to upgrade
>> from server-authenticated to mutually-authenticated within the same session.
>> That is a real market need. How about allowing a CertReq sent from the
>> server to the client in the middle of a connection, followed by the client
>> sending a Certificate and Certificate Verify. For simplicity, we could
>> always do that after the Finished, so that it's always Server-authenticated
>> session when the Finished is sent.
>>
>> Yoav
>>
>
>
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