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Re: Caching of web content based on hashes?

From: Richard Barnes <rbarnes@mozilla.com>
Date: Thu, 3 Sep 2015 14:05:09 -0400
Message-ID: <CAOAcki-a04MJPOaWJPsiHfcajWLqiQ8GBVVSnkotF9OuyFCDZA@mail.gmail.com>
To: Brad Hill <hillbrad@gmail.com>
Cc: Martin Thomson <martin.thomson@gmail.com>, Elie Bursztein <elieb@google.com>, Christian Nygaard <christiannygaard@gmail.com>, WebAppSec WG <public-webappsec@w3.org>
Yes, you could update HTTP to get this right (your particular approach
seems like an abuse of Content-Encoding, since it's not like you can decode
the content).  But that's not what SRI does :)  And in any case, you would
then only be getting a bandwidth advantage, not latency.

On Thu, Sep 3, 2015 at 1:37 PM, Brad Hill <hillbrad@gmail.com> wrote:

> + Elie Bursztein who has done a bunch of research on the topic.
>
> On Thu, Sep 3, 2015 at 9:19 AM Martin Thomson <martin.thomson@gmail.com>
> wrote:
>
>> You know that this isn't strictly a bad idea as long as you get the
>> rules right.    This might be ok...
>>
>>     GET /foo HTTP/1.1
>>     Host: example.com
>>     Accept-Encoding: hash-sha256
>>
>> Though Roy would have this defined as a new 3xx code, you might see a
>> response like:
>>
>>     HTTP/1.1 200 OK
>>     Content-Encoding: hash-sha256
>>
>>     abcdefghijklmnopqrstuvwxyz...
>>
>> That isn't caching, but at the point that you have a strong hash, it
>> doesn't matter where the content actually comes from[*].
>>
>> Of course, this is more appropriately a discussion for the HTTP working
>> group.
>>
>> [*] Much.  You still have to meet certain minimum standards of
>> confidentiality etc...
>>
>> On 3 September 2015 at 08:04, Richard Barnes <rbarnes@mozilla.com> wrote:
>> > This was discussed during the development of SRI.  It was not added
>> because
>> > it would provide the ability for a calling site to "speak for" another
>> > origin, in the sense that the browser would load the content even the
>> origin
>> > server would have sent something completely different.
>> >
>> > --Richard
>> >
>> > On Wed, Sep 2, 2015 at 5:33 PM, Christian Nygaard
>> > <christiannygaard@gmail.com> wrote:
>> >>
>> >> Is it possible to extend the Subresource integrity specification to
>> allow
>> >> for caching of web content based on hashes instead of max-age? This
>> would
>> >> allow for longer caching of objects and may speed up the web due to
>> making
>> >> cache control easier for web developers and proxies.
>> >>
>> >> http://w3c.github.io/webappsec/specs/subresourceintegrity/
>> >>
>> >> Best regards,
>> >> Christian Nygaard
>> >
>> >
>>
>>
Received on Thursday, 3 September 2015 18:05:37 UTC

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