Re: [Gen-art] Gen-ART and OPS-Dir review of draft-ietf-httpbis-header-compression-10

Herve--
I'm not sure that the text in 7.1.2 is explicit enough to be understood--
I'd be hard-pressed to define "guess" reliably. The bit that is missing,
imho, is that the provenance of the request is from a 3rd party, which is
reason to be suspicious.

An alternate wording:
An encoder seeing many 3rd party requests which contain keys whose values
never match may decided to ensure that such keys are never indexed when
going to that site, as this effectively prevents probing of the compression
context, and, if not malicious, would likely offer no benefit from indexing
anyway.

-=R



On Mon, Jan 26, 2015 at 9:29 AM, Hervé Ruellan <herve.ruellan@crf.canon.fr>
wrote:

> I tried to integrate all these comments, as well as those of Martin on
> GitHub into: https://github.com/http2/http2-spec/pull/704
>
> Hervé.
>
>
> On 01/23/2015 05:51 PM, Black, David wrote:
>
>> This sort of guidance will definitely be a useful addition.   A little
>> more wordsmithing on Stephen's proposed text follows:
>>
>>    The decision on whether a header field is ok to
>>    compress or
>>    not is highly dependent on the context. As a generic
>>    guidance, header fields used for conveying highly valued
>>    information, such as the Authorization or Cookie header
>>    fields, can be considered to be on the more sensitive
>>    side. In addition, a header field with a short value
>>    has potentially a smaller entropy and can be more at
>>    risk. We know that compressing low-entropy sensitive
>>    header fields can create vulnerabilities so such
>>    cases are most likely the ones to not compress today.
>>    Note though that the criteria to apply here may evolve
>>    over time as we gain knowledge of new attacks.
>>
>>
>> OLD
>>    We know that compressing low-entropy sensitive
>>    header fields can create vulnerabilities so such
>>    cases are most likely the ones to not compress today.
>>    Note though that the criteria to apply here may evolve
>>    over time as we gain knowledge of new attacks.
>> NEW
>>    We currently know that compressing low-entropy sensitive
>>    header fields can create vulnerabilities so compression
>>    of such fields ought to be avoided.
>>    This guidance may evolve
>>    over time as we gain knowledge of new attacks.
>>
>> Thanks,
>> --David
>>
>>  -----Original Message-----
>>> From: Stephen Farrell [mailto:stephen.farrell@cs.tcd.ie]
>>> Sent: Friday, January 23, 2015 10:45 AM
>>> To: Jari Arkko; Hervé Ruellan
>>> Cc: Martin Thomson; Black, David; ietf@ietf.org; General Area Review
>>> Team
>>> (gen-art@ietf.org); fenix@google.com; ietf-http-wg@w3.org
>>> Subject: Re: [Gen-art] Gen-ART and OPS-Dir review of draft-ietf-httpbis-
>>> header-compression-10
>>>
>>> -----BEGIN PGP SIGNED MESSAGE-----
>>> Hash: SHA1
>>>
>>>
>>>
>>> On 23/01/15 15:35, Jari Arkko wrote:
>>>
>>>>
>>>>  I made a proposal at
>>>>> https://github.com/http2/http2-spec/pull/704
>>>>>
>>>>
>>>> Looked reasonable to me.
>>>>
>>>
>>> Me too. Quibbling, I'd suggest:
>>>
>>> OLD:
>>>
>>>   The decision on whether a header field is sensitive or
>>>   not is highly dependent on the context. As a generic
>>>   guidance, header fields used for conveying highly valued
>>>   information, such as the Authorization or Cookie header
>>>   fields, can be considered to be on the more sensitive
>>>   side. In addition, a header field with a short value
>>>   has potentially a smaller entropy and can be more at
>>>   risk.
>>>
>>> NEW:
>>>
>>>   The decision on whether a header field is ok to
>>>   compress or
>>>   not is highly dependent on the context. As a generic
>>>   guidance, header fields used for conveying highly valued
>>>   information, such as the Authorization or Cookie header
>>>   fields, can be considered to be on the more sensitive
>>>   side. In addition, a header field with a short value
>>>   has potentially a smaller entropy and can be more at
>>>   risk. We know that compressing low-entropy sensitive
>>>   header fields can create vulnerabilities so such
>>>   cases are most likely the ones to not compress today.
>>>   Note though that the criteria to apply here may evolve
>>>   over time as we gain knowledge of new attacks.
>>>
>>> Cheers,
>>> S.
>>>
>>>
>>>
>>>
>>>
>>>> jari
>>>>
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>>
>