Re: [saag] Liking Linkability

Henry Story <henry.story@bblfish.net> Fri, 19 October 2012 13:46 UTC

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From: Henry Story <henry.story@bblfish.net>
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Date: Fri, 19 Oct 2012 15:46:03 +0200
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References: <CCA5E789.2083A%Josh.Howlett@ja.net> <tslzk3jsjv8.fsf@mit.edu> <201210181904.PAA07773@Sparkle.Rodents-Montreal.ORG> <FB9E461D-CA62-4806-9599-054DF24C3FD9@bblfish.net> <CAG5KPzxGz+4MywjP4knfbDr2gyvqUZc1HEBXgtaDfYT+DPg5yg@mail.gmail.com> <8AB0C205-87AE-4F76-AA67-BC328E34AF5E@bblfish.net> <CABrd9SQghpi6_rVQKxYXZDtM5HwvE7Kq7SUw5zi41ZRd3y2h9A@mail.gmail.com>
To: Ben Laurie <benl@google.com>
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Subject: Re: [saag] Liking Linkability
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On 19 Oct 2012, at 15:31, Ben Laurie <benl@google.com> wrote:

> On 19 October 2012 13:01, Henry Story <henry.story@bblfish.net> wrote:
>> 
>> On 18 Oct 2012, at 21:29, Ben Laurie <ben@links.org> wrote:
>> 
>>> On Thu, Oct 18, 2012 at 8:20 PM, Henry Story <henry.story@bblfish.net> wrote:
>>>> 
>>>> On 18 Oct 2012, at 21:04, Mouse <mouse@Rodents-Montreal.ORG> wrote:
>>>> 
>>>>>> [...]
>>>>>> Unfortunately, I think that's too high of a price to pay for
>>>>>> unlinkability.
>>>>>> So I've come to the conclusion that anonymity will depend on
>>>>>> protocols like TOR specifically designed for it.
>>>>> 
>>>>> Is it my imagination, or is this stuff confusing anonymity with
>>>>> pseudonymity?  I feel reasonably sure I've missed some of the thread,
>>>>> but what I have seem does seem to be confusing the two.
>>>>> 
>>>>> This whole thing about linking, for example, seems to be based on
>>>>> linking identities of some sort, implying that the systems in question
>>>>> *have* identities, in which case they are (at best) pseudonymous, not
>>>>> anonymous.
>>>> 
>>>> With WebID ( http://webid.info/ ) you have a pseudonymous global identifier,
>>>> that is tied to a document on the Web that need only reveal your public key.
>>>> That WebID can then link to further information that is access controlled,
>>>> so that only your friends would be able to see it.
>>>> 
>>>> The first diagram in the spec shows this well
>>>> 
>>>> http://webid.info/spec/#publishing-the-webid-profile-document
>>>> 
>>>> If you put WebID behind TOR and only have .onion WebIDs - something that
>>>> should be possible to do - then nobody would know WHERE the box hosting your
>>>> profile is, so they would not be able to just find your home location
>>>> from your ip-address. But you would still be able to link up in an access
>>>> controlled manner to your friends ( who may or may not be serving their pages
>>>> behind Tor ).
>>>> 
>>>> You would then be unlinkable in the sense of
>>>> http://tools.ietf.org/html/draft-iab-privacy-considerations-03
>>>> 
>>>> [[
>>>>     Within a particular set of information, the
>>>>     inability of an observer or attacker to distinguish whether two
>>>>     items of interest are related or not (with a high enough degree of
>>>>     probability to be useful to the observer or attacker).
>>>> ]]
>>>> 
>>>> from any person that was not able to access the resources. But you would
>>>> be linkable by your friends. I think you want both. Linkability by those
>>>> authorized, unlinkability for those unauthorized. Hence linkability is not
>>>> just a negative.
>>> 
>>> I really feel like I am beating a dead horse at this point, but
>>> perhaps you'll eventually admit it. Your public key links you.
>> 
>> The question is to whom? What is the scenario you are imagining, and who is
>> the attacker there?
>> 
>>> Access
>>> control on the rest of the information is irrelevant. Indeed, access
>>> control on the public key is irrelevant, since you must reveal it when
>>> you use the client cert.
>> 
>> You are imagining that the server I am connecting to, and that I have
>> decided to identify myself to, is the one that is attacking me? Right?
>> Because otherwise I cannot understand your issue.
>> 
>> But then I still do not understand your issue, since I deliberately
>> did connect to that site in an identifiable manner with a global id.
>> I could have created a locally valid ID only, had I wanted to not
>> connect with a globally valid one.
>> 
>> So your issue boils down to this: if I connect to a web site deliberately
>> with a global identifier, then I am globally identified by that web site.
>> Which is what I wanted.
>> 
>> So perhaps it is up to you to answer: why should I not want that?
> 
> I am not saying you should not want that, I am saying that ACLs on the
> resources do not achieve unlinkability.

Can you expand on what the dangers are?

> 
>>> Incidentally, to observers as well as the
>>> server you connect to.
>> 
>> Not when you re-negotiation I think.
> 
> That's true, but is not specified in WebID, right? Also, because of
> the renegotiation attack, this is currently insecure in many cases.

WebID on TLS does rely on TLS. Security is not a goal one can reach,
it is a way of travelling. So I do expect every security protocol to
have issues. These ones are being fixed, and if more people build on 
them, the priority of the need to fix them will grow faster.

> 
>> And certainly not if you use Tor, right?
> 
> Tor has no impact on the visibility of the communication at the server end.

You really need to expand on what the danger is. Because again
I think you are thinking of the site I am connecting to as the attacker.
But I may be wrong.

> 
>> 
>> 
>> Social Web Architect
>> http://bblfish.net/
>> 
>> 
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Social Web Architect
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