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Re: [integrity] What should we hash?

From: Devdatta Akhawe <dev.akhawe@gmail.com>
Date: Wed, 12 Mar 2014 22:24:30 -0700
Message-ID: <CAPfop_0CqRoH-Jj9MmCiEWG8ds-jezV81zxYKTgZ_z6U3G-CJQ@mail.gmail.com>
To: Mark Nottingham <mnot@mnot.net>
Cc: "public-webappsec@w3.org" <public-webappsec@w3.org>, Boris Zbarsky <bzbarsky@mit.edu>
Thanks! Intuitively, it seems there should be a simpler way to refer
to "the message payload before content codings are applied.".

What does the content-type refer to? Type of what? For example, if I
am not completely wrong, content-type of a text file with gzip
content-encoding is still text/plain and so presumably talks about
"before content codings are applied"

thanks
Dev

On 12 March 2014 17:47, Mark Nottingham <mnot@mnot.net> wrote:
> The HTTPbis docs are going to obsolete RFC2616 in a few weeks, so it's best to look at them.
>
> I think you want to say that integrity operates upon the payload of the message - see
>   http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-26#section-3.3
>
> This is after chunk encoding, gzip transfer-codings, etc. have been removed. However, content-codings are still there, e.g., for gzip, deflate in the Content-Encoding header.
>
> That's because Content-Encoding is considered a property of the representation in HTTP, even though many people implement it as a separate layer.
>
> If you want to do it before content-encoding, you'd need to specify it explicitly; e.g., as "the message payload before content codings are applied."
>
> Hope this helps,
>
> On 12 Mar 2014, at 3:58 am, Devdatta Akhawe <dev.akhawe@gmail.com> wrote:
>
>> Hi
>>
>> One key question for integrity spec is "What should the browser hash?"
>> Boris mentioned this previously
>> http://lists.w3.org/Archives/Public/public-webappsec/2013Dec/0048.html
>>
>> Informally, I am leaning towards hashing content after undoing stuff
>> like gzip, deflate, chunked-encodings etc. Does that sound reasonable?
>>
>> Next, how do we formalize (spec) this? In an ideal world, just saying
>> "undo transfer-encoding" would be enough (i.e., spec would say "hash
>> entity body"). But, common behavior is to apply gzip via
>> Content-Encoding not transfer-encoding. And we want to hash after
>> undoing gzip. (see Boris' email above)
>>
>> Mark: Do you know good specification text for this? After looking at
>> the HTTP RFC, one wording that springs to my mind is: ""After decoding
>> the entity to the media-type referenced by the content-type header"
>>
>> Thanks
>> Dev
>
> --
> Mark Nottingham   http://www.mnot.net/
>
>
>
Received on Thursday, 13 March 2014 05:26:31 UTC

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