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Re: Application Hash exchange between client and server

From: Conrad Irwin <conrad.irwin@gmail.com>
Date: Thu, 30 Jul 2015 15:43:25 +0100
Message-ID: <CAOTq_pv0ovm3nyoC8nNQ-a53f_vXzX-43A8sRTPUK0enuN+4hQ@mail.gmail.com>
To: Joel Weinberger <jww@chromium.org>
Cc: Ahmed Saleh <ahmedzs@live.ca>, "public-webappsec@w3.org" <public-webappsec@w3.org>
Thanks for the pointer. I joined the list to suggest implementing
subresource integrity as part of the Content-Security-Policy, because it
seemed like an obviously missing piece.

I don't know what the usual way of handling this is, but a pointer between
the two documents would have helped significantly.

Conrad


On Wed, Jul 29, 2015 at 11:45 PM, Joel Weinberger <jww@chromium.org> wrote:

> For your suggestion of the server sending hashes to the client, a variant
> of this is actually under design right now. See Subresource Integrity
> <http://www.w3.org/TR/SRI/> (and the many discussions on this list about
> it).
>
> For the client to server hash, this is unlikely to be implemented, for
> several reasons:
>
>    - As described, the application could lie to the server, so there
>    would be no benefit. A "bad" browser could run Chrome, get the hash it
>    sends, copy that hash, and start sending it to the server as if it was its
>    own.
>    - Even if some version were to be implemented (using TPMs, for
>    example, or even just OS level constructs), this would almost certainly be
>    a violation of the Priority of Constituencies
>    <http://www.schemehostport.com/2011/10/priority-of-constituencies.html>.
>    What you've described is a form of remote attestation
>    <https://en.wikipedia.org/wiki/Trusted_Computing#Remote_attestation>,
>    which generally has been rejected on the Web (with notable exceptions
>    surrounding DRM). Basically, a user agent *should* be allowed to lie.
>    In fact, this is how in browser compatibility traditionally has worked, and
>    why every user agent string has the words "Mozilla" and "IE" in it.
>
> --Joel
>
> On Wed, Jul 29, 2015 at 3:29 PM Ahmed Saleh <ahmedzs@live.ca> wrote:
>
>> Hi Sir/Madam,
>> It would be a nice feature if we can exchange hashes between server and
>> browser. a client as a browser would send clients' browser hash signature
>> and the server would send it's application hash signature. This way, as a
>> client, I would insure that I am communicating to the right version of
>> application I intend (in case if this application is open source) and as a
>> server, the server would insure that it's communicating to the right
>> clients' browser as intended(that for example, could protect and view my
>> data).
>> Thank you,
>>
>>
Received on Thursday, 30 July 2015 14:44:16 UTC

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