Re: [Ila] [DMM] Fwd: New Version Notification for draft-herbert-ila-mobile-00.txt

[Tom Herbert <[e-mail]>]

On Mon, Feb 5, 2018 at 10:16 PM, Lorenzo Colitti <[e-mail]> wrote:

> On Tue, Feb 6, 2018 at 3:02 PM, Tom Herbert <[e-mail]> wrote:
>
>> On Tue, Feb 6, 2018 at 2:17 PM, Tom Herbert <[e-mail]> wrote:
>>>
>>>> Section 8.3 provides the argument that singleton addresses are needed
>>>> for privacy-sensitive communications. For practicality and probably scaling
>>>> /64 is needed, however for strong privacy singleton addresses would be
>>>> needed (to avoid resorting to NAT).
>>>>
>>>
>>> You don't need singletons for privacy. You can just assign /64s that
>>> change over time.
>>>
>>
>> Yes, that seems to be the recommendation of RFC4914. However, neither
>> that RFC nor anyone else that I can tell has been able to quantitatively
>> describe the relationship between frequency of changing prefix and privacy.
>> Any statements about this are qualitative in nature. By intuition, it might
>> be believable that higher frequency should mean better privacy, but nobody
>> can quantify that. So for a user where privacy is paramount, my example is
>> a political dissident that is anonymously criticizing their government,
>> there is no definitive answer to give then when they ask what frequency
>> they need to ensure their privacy. Besides that, I believe that any
>> frequency could be defeated with the postulated exploit below (if you see a
>> flaw in this logic please let me know).
>>
>
> In general, any scheme that relies in changing singletons can be
> implemented by changing /64 prefixes in the same way.
>
> Lorenzo,

The number of unique /64 prefixes a network could assign for this purpose
is much less than 2^64 due to network prefix and a prefix needed for
internal routing.


> Your example of a dissident that is criticizing the government is not a
> relevant one in the likely case that the
>

Consider that the dissident might be exiled in a country that is
sympathetic to their cause, and the government being criticized has no
control over the local provider. There are several famous individuals for
which this is true, protecting their anonymity and location may be a matter
life and death.


> government has the power to compel the network operator to log all the
> singletons that the network assigns.
>
>
Then the government should have the power to compel an operator to log NAT
mappings, but apparently that hasn't happened or isn't sufficient for what
law enforcement thinks they need. I suspect that the primary reason that LI
wants trackable addresses in the Internet is to perform mass passive
surveillance on transit networks in their jurisdiction to deduce criminal
networks and intent.


> Actually, there is one frequency where the privacy effects can be
>> qualified: that is to use a different address per connection. This is
>> effectively what stateful NAT provides and why law enforcement doesn't like
>> it. With a large enough pool of users behind a NAT, flows sourced form the
>> same device cannot be correlated by a third party in external network. This
>> is strong privacy privacy in addressing (properties listed in 8.3). In lieu
>> of telling the political dissident to find a provider using NAT, assigning
>> addresses for singe use can provide it. Assigning a /64 to every flow won't
>> scale, but singleton addresses could.
>>
>
> Saying that assigning unaggregatable singleton addresses to each flow
> would scale is an extremely bold statement. Back-of-the-envelope says that
> with 100M devices and an average of 10 flows per device that last 5 minutes
> on average you've got 1B entries and 3.3 milion flow updates per second.
> That amount of state must be available within a reasonable time (line rate,
> or, say, 1 RTT) to any border router that could conceivably receive a
> packet for any one of those flows. I don't know what sort of hardware you'd
> be able to run that on, nor who would want to make such a colossal
> infrastructure investment even if it could be done.
>

Here are some mitigating factors for scaling issue:

1) Not all communications require strong privacy, so they all don't need
singleton addresses.
2) The amount of state is equal, or at least proportional, to that in a
network using NAT today. Scaling single use addresses then scales as much
as NAT scales.
3) As pointed out in section 8.3 it is conceivable that crypto-graphic
addresses might be used that would allow a method of address aggregation
that a provider network knows about but is hidden to the rest of the world.
I think this possibility is worth investigation.

Tom