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Re: Does no-store in request imply no-cache?

From: Mark Nottingham <mnot@mnot.net>
Date: Mon, 18 Oct 2010 11:26:46 +1100
Cc: HTTP Working Group <ietf-http-wg@w3.org>
Message-Id: <31C383BE-B5AD-4B10-B278-CA4A05702DF9@mnot.net>
To: David Morris <dwm@xpasc.com>
I'm not disputing that a response to a request with 'no-store' can't be used to satisfy subsequent requests; the spec is pretty clear about that.

The question at hand is whether a request containing 'no-store', when received by a cache, can be served from cache, or whether it implies 'no-cache.' I.e., it's not whether the response can be used in a subsequent response; it's whether a previous response can be used to satisfy it.

Using a cached response to satisfy a request with 'no-store' in it doesn't result in leakage of information, all other things being equal. 

Cheers,




On 18/10/2010, at 11:22 AM, David Morris wrote:

> 
> I don't see it as orthogonal ... no-store means no-store ... my reading
> is still that it can't be satisfied from the cache (i'm assuming that
> the cache entry was stored as the result of a request w/o no-store).
> 
> If you can't cache the result, you can't use the cache to provide the
> result. It may be that the data being protected is the association
> between this request and the response. Or what ever. I think the
> cache should be ignored for a no-store request and of course if the
> no-store first appears on the response, the new response would not
> be cached, even if it would logically invalidate existing content.
> 
> On Mon, 18 Oct 2010, Mark Nottingham wrote:
> 
>> Right, but that's largely orthogonal to the question below; whether
>> no-store in a request implies that a previously stored response needs to
>> be invalidated.
>> 
>> Cheers,
>> 
>> 
>> On 18/10/2010, at 11:05 AM, David Morris wrote:
>> 
>>> 
>>> I interpret NOSTORE as a stricter restriction than NOCACHE.
>>> If it can't be stored, it can't be used in a subsequent
>>> response.
>>> 
>>> If I recall the discussion from 10 years ago correctly, the
>>> intent was to reduce the posibility that private information
>>> could leak via even temporary storage.
>>> 
>>> Dave Morris
>>> 
>>> On Mon, 18 Oct 2010, Mark Nottingham wrote:
>>> 
>>>> Thoughts re: the below?
>>>> 
>>>> My inclination is to clarify "any response to it" so that a cache can
>>>> use the same cached response to serve multiple requests with no-store in
>>>> them (or not).
>>>> 
>>>> Cheers,
>>>> 
>>>> 
>>>> Begin forwarded message:
>>>> 
>>>>> From: Alex Rousskov <rousskov@measurement-factory.com>
>>>>> Date: 23 September 2010 9:47:57 AM AEST
>>>>> To: Mark Nottingham <mnot@yahoo-inc.com>
>>>>> Cc: Squid Developers <squid-dev@squid-cache.org>
>>>>> Subject: Re: Does no-store in request imply no-cache?
>>>>> 
>>>>> On 09/22/2010 05:05 PM, Mark Nottingham wrote:
>>>>> 
>>>>>> Strictly, as a request directive it means "you can't store the
>>>>>> response to this request" -- it says nothing about whether or not you
>>>>>> can satisfy the request from a cache.
>>>>> 
>>>>> Hi Mark,
>>>>> 
>>>>>  Let's assume the above is correct and Squid satisfied the no-store 
>>>>> request from the cache. Should Squid purge the cached response afterwards?
>>>>> 
>>>>> If Squid does not purge, the next regular request will get the same 
>>>>> cached response as the no-store request got, kind of violating the "MUST 
>>>>> NOT store any response to it" no-store requirement.
>>>>> 
>>>>> If Squid purges, it is kind of silly because earlier requests could have 
>>>>> gotten the same "sensitive" information before the no-store request came 
>>>>> and declared the already cached information "sensitive".
>>>>> 
>>>>> Thank you,
>>>>> 
>>>>> Alex.
>>>>> 
>>>>> 
>>>>>> See also:
>>>>>> http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-11#section-3.2.1
>>>>>> 
>>>>>> 
>>>>>> On 23/09/2010, at 4:27 AM, Alex Rousskov wrote:
>>>>>> 
>>>>>>> Hello,
>>>>>>> 
>>>>>>>  One interpretation of RFC 2616 allows the proxy to serve hits when
>>>>>>> the request contains "Cache-Control: no-store". Do you think such an
>>>>>>> interpretation is valid?
>>>>>>> 
>>>>>>> no-store
>>>>>>>    The purpose of the no-store directive is to prevent the
>>>>>>>    inadvertent release or retention of sensitive information (for
>>>>>>>    example, on backup tapes). The no-store directive applies to the
>>>>>>>    entire message, and MAY be sent either in a response or in a
>>>>>>>    request. If sent in a request, a cache MUST NOT store any part of
>>>>>>>    either this request or any response to it.
>>>>>>> 
>>>>>>> Thank you,
>>>>>>> 
>>>>>>> Alex.
>>>> 
>>>> --
>>>> Mark Nottingham   http://www.mnot.net/
>>>> 
>>>> 
>>>> 
>>>> 
>>> 
>> 
>> --
>> Mark Nottingham   http://www.mnot.net/
>> 
>> 
>> 
>> 

--
Mark Nottingham   http://www.mnot.net/
Received on Monday, 18 October 2010 00:27:19 GMT

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