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Using HTTP Trailers [was: Content-Integrity header]

From: Mark Nottingham <mnot@mnot.net>
Date: Wed, 11 Jul 2012 09:59:02 +1000
Cc: Amos Jeffries <squid3@treenet.co.nz>, "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>
Message-Id: <02DA460A-7330-41FB-8174-57FE16683487@mnot.net>
To: "Ludin, Stephen" <sludin@akamai.com>
chunk-extensions aren't widely supported in APIs, and usually dropped hop-by-hop (then again, trailers can be too).

Some discussion of trailer support in Apache:
  http://apache-http-server.18135.n6.nabble.com/HTTP-trailers-td4796242.html

 and using Trailers to surface debug information in Firebug:
  https://groups.google.com/forum/?fromgroups#!topic/firebug/v5ldjoVThH8

(yes, this is a bit of a project for me)

Finally, I know some server-side implementers would would LOVE to be able to set things like ETag and Last-Modified in trailers, and have them used by caches...

Cheers,


On 11/07/2012, at 4:33 AM, Ludin, Stephen wrote:

> I really like the idea of placing the Digest in the chunk trailers.  Being
> able to calculate these digests on the fly and not buffer the entire
> message is critical in my opinion.
> 
> Another concept that I have been playing with is providing digests on
> individual chunks using chunk-extension.  The rational for this is for
> very large objects.  With per-chunk digests the client would have the
> ability to re-request a specific corrupted section of an object using a
> range request rather than the entire object.  This can have enormous
> perceived performance and reliability benefits for consumers of things
> such as software download and large media files.
> 
> I was working on a draft to propose this, but I didn't feel it was well
> baked enough to share.  If there is interest in this type of functionality
> I will polish it up and post it.
> 
> One issue to point is is that for these types of "frame" based integrity
> checks I generally feel like we are reinventing the content integrity
> portion of SSL/TLS.  Though I see the value in begin able to do this apart
> from SSL it forces the question at what point do you just switch over to
> SSL to get the desired functionality?
> 
> -stephen
> 
> 
> 
> On 7/9/12 4:00 PM, "Amos Jeffries" <squid3@treenet.co.nz> wrote:
> 
>> On 10.07.2012 07:08, HAYASHI, Tatsuya wrote:
>>> +1
>>> 
>>> I know that this is demanded.
>>> When I discussion about http-authentication and phishing,
>>> it is requested by many people.
>>> It is a difficult problem.
>>> ex) proxy...
>>> 
>>> I think that it is good to do this discussion now.
>>> 
>>> ---
>>> Tatsuya
>>> 
>>> On Sat, Jul 7, 2012 at 8:23 AM, James M Snell wrote:
>>>> In general, I'm +1 on the general idea albeit with a few caveats...
>>>> 
>>>> 1. To minimize complexity, only a single Content-Integrity header
>>>> should be used. I don't want, as Roy points out, to have to iterated
>>>> through a bunch of unsupported header values looking for the one I
>>>> want. Just as it makes very little sense for an implementor to
>>>> provide
>>>> multiple Last-Modified, Etag and Content-Type headers in a single
>>>> message; there should be only a single Content-Integrity statement
>>>> and
>>>> I either understand it or I don't.
>> 
>> Either the client advertises what it supports (opening itself to
>> middleware erasing options they can't modify). Or the server uses
>> multiple algorithms in hopes that the middleware cannot violate them
>> all.
>> It makes perfect sense to have several levels of integrity check. MD5,
>> SHA1, AES in one response and allow the client to validate the strongest
>> it can handle.
>> 
>> There is also an arguable case for middleware wanting to add its own
>> hash to inform the client essentially "this is what I got given". So the
>> point of manipulation can be back-traced when the more secure end-to-end
>> checks fail.
>> 
>> If you want end-to-end integrity, don't stop at half measures.
>> Particularly at half measures which can be corrupted.
>> 
>> 
>>>> 
>>>> 2. The performance impact of calculating the digest needs to be
>>>> carefully considered. I'd rather not be required to buffer a full
>>>> representation in memory all the time just to calculate a header
>>>> value. I know it's largely unavoidable, but perhaps there's some
>>>> currently elusive solution that can be considered. For instance..
>>>> allowing Content-Integrity to appear as a trailer at the end of a
>>>> chunked response.
>> 
>> As has been said Trailers happen here.
>> 
>>>> 
>>>> 3. Something needs to be said about what happens if the
>>>> Content-Integrity check fails. For instance, if a request containing
>>>> Content-Integrity is sent to the server and the server detects that
>>>> the signature is invalid, what should happen? what must happen?
>>>> Likewise, how are intermediaries expected to treat the
>>>> Content-Integrity header given that any intermediary is able to
>>>> modify
>>>> the payload at any time?
>> 
>> This is going to be most useful on request/responses sent with
>> "no-transform" of course.
>> If the integrity was only a MD5 or SHA1 hash which middleware can edit
>> easily there is no end-to-end integrity, just hop-by-hop integrity.
>> 
>> 
>> Also, there has to be a mutual secret between origin server and client.
>> Without that, when integrity is compromised the transforming hop will
>> simply erase or replace the Content-Integrity header value. A secret key
>> unknown to that middleware is required to make the integrity hash break
>> when it tries this.
>> 
>> AYJ
>> 
> 
> 

--
Mark Nottingham
http://www.mnot.net/
Received on Tuesday, 10 July 2012 23:58:56 GMT

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