Re: [P2PSIP] Ben Campbell's No Objection on draft-ietf-p2psip-share-09: (with COMMENT)

"Thomas C. Schmidt" <t.schmidt@haw-hamburg.de> Fri, 04 November 2016 22:51 UTC

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To: Ben Campbell <ben@nostrum.com>
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From: "Thomas C. Schmidt" <t.schmidt@haw-hamburg.de>
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Subject: Re: [P2PSIP] Ben Campbell's No Objection on draft-ietf-p2psip-share-09: (with COMMENT)
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HI Ben,

On 04.11.2016 23:17, Ben Campbell wrote:

>>>>> ----------------------------------------------------------------------
>>>>> COMMENT:
>>>>> ----------------------------------------------------------------------
>>>>>

>>>>  ... then you identify the user in the ACL and walk up the
>>>> delegation
>>>> chain.
>>>>
>>>> In step 5, you have arrived at the root of the delegation tree. This
>>>> is the case, when the to_user equals the signer equals the owner of
>>>> the resources (see see Figure 1). This is also how it terminates -
>>>> the
>>>> owner of the resource is the root of the trust chain.
>>>
>>> I'm probably being dense here, but my confusion is in the phrasing of
>>> "the "to_user" value user name of the signer of the previously
>>> selected
>>> ACL item".  Won't that always be true for every ACL item up the chain
>>> after the first?
>>>
>>
>> No, the selected ACL item from the previous step is the row you are
>> in. It basically says that the "to_user" value equals the username of
>> the signer. This is the "A  A" case in row 4 in your example below.
>> This row should be in an ACL only once and the user must be the owner
>> of the resource, which is requested to be verified separately.
>>
>>> As an example, Lets say I have a delegation chain of A,B,C,D, where A
>>> is
>>> the owner. Would the ACL chain look like the following (in
>>> leave-to-root
>>> order )?
>>>
>>>    signer to_user
>>> 1   C        D
>>> 2   B        C
>>> 3   A        B
>>> 4   A        A
>>>
>>> If so, then ACL 2 seems to have a to_user that matches the signer of
>>> ACL
>>> 1 (the previously selected ACL), which seems to terminate early.
>>>
>>> Again, I'm sure I'm missing something.
>>>
>>
>> I believe the confusion comes from the "previously" - this is meant to
>> refer to the "previous step" and the actual row. We changed
>> "previously" to "previous step" to avoid this confusion.
>
> I still think I'm confused. Step 5 basically says iterate over steps 3
> and 4. If I'm currently looking at the ACL from the Nth iteration of 3
> and 4, it seems to me that the "ACL from the previous step" is ACL N-1.
>

The delegation is a tree - so it's not a linear chain.

> If the terminal condition is when you find an ACL where the signer and
> the to_user are the same, then I you could say _that_ without getting
> into "previous steps."
>

Guess you are right. Why don't we simplify the sentence to

"Repeat steps 3 and 4 until the "to_user" value is equal to the user 
name of the signer of the ACL in the selected item." ?

Thanks,
  thomas

-- 

Prof. Dr. Thomas C. Schmidt
° Hamburg University of Applied Sciences                   Berliner Tor 7 °
° Dept. Informatik, Internet Technologies Group    20099 Hamburg, Germany °
° http://www.haw-hamburg.de/inet                   Fon: +49-40-42875-8452 °
° http://www.informatik.haw-hamburg.de/~schmidt    Fax: +49-40-42875-8409 °