Re: [Mobopts] Review of draft-irtf-mobopts-location-privacy-solutions-06

[Rajeev Koodli <[e-mail]>]

Hi Vijay,


On 11/5/07 3:28 PM, "ext Vijay Devarapalli"
<[e-mail]> wrote:

> Hello,
> 
> I reviewed the draft. It still needs a lot of work.
> 
> Section 4.1
> -----------
> Section 4.1 is not making sense to me. The pseudo home address
> changes every time return routability is run. It also changes
> every time the CoA changes. Why does it have to change so often?
> 
> Isn't one pseudo home address per session with a correspondent
> node sufficient?
> 

The pseudo HoA changing at each run of the RR provides some protection
against profiling. Change of CoA upon handover, or a new CoA nonce index or
a new RFC 3041 style CoA configuration makes a round of RR to be run. The
pseudo HoA itself is not inducing new signaling, but a few computational
steps.


> Shouldn't the following be?
> 
>>   privacy keygen token = First (64, Kcn(Home Init Cookie | nonce | 2))
> 
> privacy keygen token = First (64, HMAC_SHA1(Kcn, (Home Init Cookie |
>                                      nonce | 2))

Yes. Noted. 


> 
>>    When a correspondent node receives a Binding Update with a new
>>    destination option carrying the pseudo home address, it must first
>>    compute Kpm as above.
> 
> You probably meant "a destination option carrying a new pseudo home
> address". The home address destination option is always present in
> the BU.
> 

Actually, there is a new Type number for the Destination Option containing
the pseudo HoA, so that the CN can first compute the String and recover the
HoA.


>>    The computation is similar to how it would
>>    compute Kbm, except that the privacy keygen token is computed with
>>    the home address set to all zeros.
> 
> Earlier in section 4.1, the computation of privacy keygen token is
> shown as
> 
>     privacy keygen token = First (64, Kcn(Home Init Cookie | nonce | 2))
> 
> The home address is not used in this computation. So why is the home
> address set to all zeros?
> 

The text above (about HoA being set to zero) must be removed. It is still
lingering around from the previous version.


>> The correspondent node then
>>    stores the nonce indices, and Kbm itself.  It may also send a normal
>>    Binding Acknowledgment to the mobile node.
> 
> Wouldn't this defeat the purpose? The CN should include the pseudo
> home address in the routing header in the binding ack. What does
> "normal Binding Acknowledgment" mean?
> 

"normal" means a regular Back, but you are right it should include the
pseudo HoA.


>>    The privacy management key Kpm can be the same as the binding
>>    management key Kbm and the mobile node generates the pseudo home
>>    address as follows:
>> 
>>       pseudo home address = Enc(Kpm, home address)
>> 
>>       Where Enc(.) is a symmetric key encryption algorithm, for example,
>>       AES.
> 
> hmm... You would need to pick *an* encryption algorithm and convey
> the same to the CN. How would both ends pick the same algorithm
> otherwise?

Right.

> 
> Section 5
> ---------
> I am not sure why section 5 is needed at all. There is absolutely
> no need to generate a pseudo home address with the home agent. The
> MN can always use ESP in tunnel mode for MIPv6 signaling messages
> and hide the home address from the access link. I suggest removing
> sections 5.1, 5.2 and 5.3.
> 

You mean in relation to Section 4, this offers no additional benefits?

Thanks for the review.

-Rajeev
-- 
http://people.nokia.net/~rajeev


> Section 5 also does not take into account scenarios where there
> might not be a shared key between the MN and the HA. It also does
> not account for scenarios where the home agent allocates a home
> address for the mobile node as part of MIPv6 bootstrapping.
> 
> I stopped reviewing here. :)
> 
> Vijay
> 
> 
> 
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