Re: [TLS] chairs - please shutdown wiretapping discussion...

Stephen Farrell <stephen.farrell@cs.tcd.ie> Mon, 10 July 2017 19:32 UTC

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To: "Blumenthal, Uri - 0553 - MITLL" <uri@ll.mit.edu>, "tls@ietf.org" <tls@ietf.org>
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From: Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Subject: Re: [TLS] chairs - please shutdown wiretapping discussion...
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On 10/07/17 20:07, Blumenthal, Uri - 0553 - MITLL wrote:
> My $0.02: absolutely not on the Standards Track (for reasons already
> expressed by others), might be discussable if Informational.

I haven't checked, but as far as I recall, other wiretapping
RFCs inconsistent with 2804 have all been in the ISE stream
(or predate it) and have all documented already deployed
wiretapping schemes. I think that is consistent with 2804 and
using a WG list and WG participant cycles/attention to
debate/develop wiretapping methods does go against 2804 and
ought not be done.

S.

> 
> -- Regards, Uri Blumenthal
> 
> On 7/10/17, 15:03, "TLS on behalf of Nico Williams"
> <tls-bounces@ietf.org on behalf of nico@cryptonector.com>; wrote:
> 
> On Mon, Jul 10, 2017 at 08:01:32PM +0300, Yoav Nir wrote:
>>> On 10 Jul 2017, at 17:16, Stephen Farrell
>>> <stephen.farrell@cs.tcd.ie>; wrote:
>>>> 2.  this proposal offers significantly better security
>>>> properties than current practice (central distribution of
>>>> static RSA keys)
>>> 
>>> I fail to see any relevant difference in security properties 
>>> between those two, never mind a significant improvement.
>> 
>> I can see one way in which it is worse.
>> 
>> With static RSA keys, you can configure the server to use only PFS 
>> ciphesuites (ECDHE-RSA or DHE-RSA). If you want to enable the
>> non-FS, you need to switch to RSA ciphersuites, and that would be
>> obvious to any client.  In fact, I think today a server would stick
>> out if it only supported RSA ciphersuites.
>> 
>> There is no way to know that a server is doing what it says in the 
>> draft. It’s completely opaque to the client.
>> 
>> However, in both cases the server does get FS. As long as the
>> server has not enabled RSA ciphersuites or exportable private key
>> shares, any recorded TLS stream is safe even if the attacker later
>> gets the private key.
> 
> Well, a client could observe reuse of server ECDHE public keys...
> 
> And servers can always share session keys with an auditing system. 
> There's no way a client could detect this.
> 
> I don't think we need to have the client KNOW what the server is
> doing because... how the heck can the server prove it's not
> publishing the client's secrets??  The server simply cannot prove
> that it is adhering to any privacy policy.
> 
> Brief reuse of server ECDHE public keys is an optimization.  I
> _think_ it's a safe optimization, and it's safer the shorter the
> reuse period is -- and correspondingly less safe the longer the reuse
> period.
> 
> But I would prefer that anyone wanting auditability just build that
> into their implementations as a proper audit capability.  Yes, it's
> more complex to later decrypt sessions, but it also doesn't mess with
> the protocol in any way.
> 
> That said, I wouldn't object to the proposal if it meant to be 
> Informational.  I don't see how a document that describes a possible
> a configuration (not protocol!) that is not relevant to the Internet 
> should be a Standards-Track RFC, or BCP for that matter.
> Informational will do.
> 
> Nico --
> 
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> 
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