Re: Comments on Explicit/Trusted Proxy

Roberto Peon <grmocg@gmail.com> Fri, 03 May 2013 00:54 UTC

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Date: Thu, 2 May 2013 17:53:31 -0700
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From: Roberto Peon <grmocg@gmail.com>
To: "Adrien W. de Croy" <adrien@qbik.com>
Cc: Peter Lepeska <bizzbyster@gmail.com>, HTTP Working Group <ietf-http-wg@w3.org>
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Subject: Re: Comments on Explicit/Trusted Proxy
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The scheme allows for injection of bytes, but not within any of the secure
tunnels. Instead, the proxy's bytes are clearly demarqued as different.

The idea here is that the client or server should always know when the
proxy has changed bytes, and it shouldn't, though it may inject
bytes/requests/whatever in either direction.


Sure, a client cert is one way of authenticating to the server. I didn't go
into that much detail, but rather pointed out that the scheme proposed in
that doc, that servers may decide they don't want to service queries from
(some) proxies, and direct the client to either try directly, or allow the
request to fail.

-=R

On Thu, May 2, 2013 at 5:48 PM, Adrien W. de Croy <adrien@qbik.com>; wrote:

>
> proxies need to be able to modify the bytes or at least inject messages
> back to the client.
>
> e.g.
>
> * request denied by policy (e.g. you can't POST to that site due to DLP
> rules)
> * serving from cache
> * ad stripping
> * malware blocking
> * etc etc etc
>
> let alone stripping hop-by-hop headers etc
>
> So I don't think anyone will bother with a scheme that doesn't allow for
> that.  If the only option of the intermediary is to delay or drop the
> connection, the client is going to be in the dark as to why.  Already the
> user experience in this area is poor.
>
> As for intercepting proxies.  Whilst I agree they are a PITN, they are
> strongly favoured by customers for several obvious reasons.
>
> Until we can get a wide-spread mechanism deployed to securely FORCE
> clients to use a proxy, we're going to see interception.
>
> As for MITM.  Whilst we continue to think of it as an attack, we will
> continue to see resistance.  It's clear some people see it only negatively,
> where others see this as an opportunity to improve things compared to
> current MITMs.
>
> Personally I would rather know what is going on, than be in the dark and
> be forced to swallow whatever I receive simply because I was forced (by
> company policy) to install a root cert for the spoofed certs.  Sites using
> EV certs will show me what is going on if I know a site uses EV certs,
> since the EV breaks on spoofed certs.  Or I need to check the cert path on
> any site to see if I can find the forced cert at the root.  But that's me,
> not everyday punters.
>
> As for the server trusting the proxy.  Why is that any different to the
> server trusting the client.  Use a client cert.  Can always fall back to a
> tunnel if the server indicates it needs a client cert.  Currently there's
> no way around this issue in today's MITM systems except for installing the
> client cert on the proxy.
>
> Adrien
>
>
> ------ Original Message ------
> From: "Roberto Peon" <grmocg@gmail.com>;
> To: "Peter Lepeska" <bizzbyster@gmail.com>;
> Cc: "HTTP Working Group" <ietf-http-wg@w3.org>;
> Sent: 3/05/2013 12:13:21 p.m.
> Subject: Re: Comments on Explicit/Trusted Proxy
>
>  responses inline.
>
>
>  On Thu, Apr 25, 2013 at 1:38 PM, Peter Lepeska <bizzbyster@gmail.com>;
>  wrote:
>
>> Some comments on Roberto's doc:
>>
>>   In the case where the user-agent has been configured with Chris as a
>>    trusted-proxy, either Anne's connect-stream MUST use either a null-
>>    cipher, or Anne MUST provide the decryption key material to Chris
>>    immediately after tunnel establishment, and before any data traverses
>>    the tunnel.
>>
>>
>> This seems like a showstopper to me. Even if we can get past the problems
>> associated with a trusted proxy in general, I can't see getting acceptance
>> of any approach that involves sending a session key from one machine to
>> another. But why not just use two full SSL sessions like the typical MITM
>> proxy (http://crypto.stanford.edu/ssl-mitm/or http://mitmproxy.org/)
>> approach? But instead of forging certificates like they do, just give the
>> trusted proxy its own certificate and then display both the trusted proxy
>> certificate and the content server certificate in the browser when the user
>> wants info about the two point-to-point SSL sessions.
>>
>>
> Using two connections may require two separate connections at the eventual
> endpoint, and it contributes to bufferbloat.
> Also, the proxy may wish to influence the private channel (e.g. don't talk
> to site X). With connection sharing, this is difficult/impossible otherwise
> (that other connection may not only go to example.com).
>
>
>>  "For the purpose of this document, it is assumed that the user locates
>>
>>    a piece of paper upon a wall and reads it, typing these proxy
>>    settings into a configuration field for their user-agent.  This is
>>    obviously not the only possible configuration mechanism, but it may,
>>    sadly, be the most secure.  It is assumed that alternate distribution
>>    techniques may be discussed.
>>
>> "
>>
>> While explicit proxy configuration may be the most secure, it is very
>> difficult to manage for mobile devices especially, as others have mentioned
>> on this list. Transparent interception is the more widely adopted approach
>> -- not because of security but because of stability and manageability.
>>
>>
> There is no secure automatic proxy configuration unless a completely
> separate trust chain is somehow created and is reliable (or at least moreso
> than what we have with TLS today).
> Transparent proxying causes problems in upgrading the protocol as nobody
> knows where the problem lies. If this wasn't such a painful point, we'd
> have been using SPDY over port 80...
> I'm fundamentally opposed to transparent proxying because it makes
> protocol evolution next to impossible when you can't figure out who is
> messing up...
>
>
>
>>  What about "transparent" proxies that advertise themselves? Is it
>> possible to use NPN (
>> https://technotes.googlecode.com/git/nextprotoneg.html) to advertise the
>> presence of an intercepting proxy for 443 traffic? Then the user can be
>> notified that a proxy wants to be trusted for X reasons and the user would
>> then make the opt in or opt out decision. Then, similar to SPDY, the
>> presence of the trusted proxy in the end-to-end path could be signaled to
>> the end user via icons in the browser.
>>
>
>
>
>
>>
>> MITM is used today with no user knowledge. At least in this approach, a
>> user has the ability to opt in or out and to also be aware of the presence
>> of the intermediate proxy.
>>
>
> That is the idea.
> Additionally, and this is important, the server gets to decide if the MITM
> is acceptable, and, in the proposed scheme the MITM doesn't get to modify
> bytes. It merely gets to advise the recipient of how to deal with them,
> delay them, or disconnect.
>
> -=R
>
>
> On Thu, Apr 25, 2013 at 1:38 PM, Peter Lepeska <bizzbyster@gmail.com>wrote:
>
>> Some comments on Roberto's doc:
>>
>>   In the case where the user-agent has been configured with Chris as a
>>    trusted-proxy, either Anne's connect-stream MUST use either a null-
>>    cipher, or Anne MUST provide the decryption key material to Chris
>>    immediately after tunnel establishment, and before any data traverses
>>    the tunnel.
>>
>>
>> This seems like a showstopper to me. Even if we can get past the problems
>> associated with a trusted proxy in general, I can't see getting acceptance
>> of any approach that involves sending a session key from one machine to
>> another. But why not just use two full SSL sessions like the typical MITM
>> proxy (http://crypto.stanford.edu/ssl-mitm/ or http://mitmproxy.org)
>> approach? But instead of forging certificates like they do, just give the
>> trusted proxy its own certificate and then display both the trusted proxy
>> certificate and the content server certificate in the browser when the user
>> wants info about the two point-to-point SSL sessions.
>>
>> "For the purpose of this document, it is assumed that the user locates
>>
>>    a piece of paper upon a wall and reads it, typing these proxy
>>    settings into a configuration field for their user-agent.  This is
>>    obviously not the only possible configuration mechanism, but it may,
>>    sadly, be the most secure.  It is assumed that alternate distribution
>>    techniques may be discussed.
>>
>> "
>>
>> While explicit proxy configuration may be the most secure, it is very
>> difficult to manage for mobile devices especially, as others have mentioned
>> on this list. Transparent interception is the more widely adopted approach
>> -- not because of security but because of stability and manageability.
>>
>> What about "transparent" proxies that advertise themselves? Is it
>> possible to use NPN (
>> https://technotes.googlecode.com/git/nextprotoneg.html) to advertise the
>> presence of an intercepting proxy for 443 traffic? Then the user can be
>> notified that a proxy wants to be trusted for X reasons and the user would
>> then make the opt in or opt out decision. Then, similar to SPDY, the
>> presence of the trusted proxy in the end-to-end path could be signaled to
>> the end user via icons in the browser.
>>
>> MITM is used today with no user knowledge. At least in this approach, a
>> user has the ability to opt in or out and to also be aware of the presence
>> of the intermediate proxy.
>>
>> Thoughts?
>>
>> Peter
>>
>>
>>  On Apr 24, 2013, at 12:49 PM, William Chan (陈智昌) <willchan@chromium.org>;
>> wrote:
>>
>>  Yep, but no, it hasn't gone anywhere.
>>
>>
>> On Wed, Apr 24, 2013 at 7:44 AM, Peter Lepeska <bizzbyster@gmail.com>wrote:
>>
>>> Hi William,
>>>
>>> Is this draft by Roberto Peon the one you were referring to?
>>>
>>> http://tools.ietf.org/html/draft-rpeon-httpbis-exproxy-00
>>>
>>> Has this gone anywhere?
>>>
>>> I'm looking to design and build a "trusted proxy" that aligns with the
>>> browser development roadmap/vision in order to provide web acceleration
>>> functionality and so would like to get involved in this process if still
>>> active.
>>>
>>> Thanks,
>>>
>>> Peter
>>>
>>>
>>> On Mon, Apr 30, 2012 at 5:57 PM, William Chan (陈智昌) <
>>> willchan@chromium.org>; wrote:
>>>
>>>> On the contrary, I think it's great to have multiple proposals. If you
>>>> have your own vision for how this should work, please send it out! :) My
>>>> statement was simply an FYI, not a "back off, we've got this!"
>>>>
>>>> On Mon, Apr 30, 2012 at 2:45 PM, Peter Lepeska <bizzbyster@gmail.com>wrote:
>>>>
>>>>> Perfect then I'll sit tight.
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Peter
>>>>>
>>>>>
>>>>> On Mon, Apr 30, 2012 at 5:43 PM, William Chan (陈智昌) <
>>>>> willchan@chromium.org>; wrote:
>>>>>
>>>>>> FYI, we (google spdy team) have been discussing a "trusted proxy"
>>>>>> internally and I think Roberto's got a draft in the works.
>>>>>>
>>>>>>
>>>>>> On Mon, Apr 30, 2012 at 2:22 PM, Peter Lepeska <bizzbyster@gmail.com>wrote:
>>>>>>
>>>>>>> Hi Mark,
>>>>>>>
>>>>>>> Earlier this group discussed the idea of a "trusted proxy". Does
>>>>>>> that fall under the HTTP/2.0 category?
>>>>>>>
>>>>>>> I may have some cycles for this.
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>> Peter
>>>>>>>
>>>>>>>
>>>>>>> On Fri, Apr 27, 2012 at 1:28 AM, Mark Nottingham <mnot@mnot.net>wrote:
>>>>>>>
>>>>>>>> Just a reminder that we're still accepting proposals for:
>>>>>>>>
>>>>>>>> 1. HTTP/2.0
>>>>>>>> 2. New HTTP authentication schemes
>>>>>>>>
>>>>>>>> As per our charter <http://datatracker.ietf.org/wg/httpbis/charter/
>>>>>>>> >.
>>>>>>>>
>>>>>>>> So far, we've received the following proposals applicable to
>>>>>>>> HTTP/2.0:
>>>>>>>>  <http://trac.tools.ietf.org/wg/httpbis/trac/wiki/Http2Proposals>
>>>>>>>>
>>>>>>>> But none yet for authentication schemes:
>>>>>>>>  <http://trac.tools.ietf.org/wg/httpbis/trac/wiki/HttpAuthProposals
>>>>>>>> >
>>>>>>>>
>>>>>>>> As communicated in Paris, the deadline for proposals is 15 June,
>>>>>>>> 2012. It's fine if your proposal isn't complete, but we do need to have a
>>>>>>>>  good sense of it by then, for discussion.
>>>>>>>>
>>>>>>>> Regards,
>>>>>>>>
>>>>>>>> --
>>>>>>>> Mark Nottingham   http://www.mnot.net/
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>>
>