My numbers show that on a network, the probablity is so small that the
address is statistically unique.
Even with 50,000 devices on a network, the probably would be 6.67E-9%
Just not there.
On 07/20/2016 02:27 PM, Pascal Thubert (pthubert) wrote:
Thanks Bob!
I think the bottom line here is what's the exposure. If the collision occurred
on a MAC address that would effectively get packets to the wrong place and
would partially cut off devices from the network.
No such thing here. The collision has no operational consequence. Both nodes
will register their addresses fine and there will be no visible effect unless
the IPv6 addresses are also in collision.
Is there a security opening then?
The exposure is that two devices may be capable of claiming one another's
address and the 6LBR will fail to prevent this, putting us back to today's
situation for these 2 particular devices.
Even in the highly remote chance that they are on a same subnetwork, even if
one is a really mean device, L2 crypto does not allow node B to see what UID is
used by device A so those 2 devices will not know they are in this situation.
It's good to add words to explain all this but the chance of accident are too
remote to be of consequence. Instead we need to focus on getting a CGA that is
hard enough to attack....
Regards,
Pascal
Le 20 juil. 2016 à 13:17, Robert Moskowitz <[email protected]> a écrit :
On 07/20/2016 11:59 AM, Mohit Sethi wrote:
Dear Behcet and Pascal
I have previously reviewed the draft on address protected neighbor discovery:
draft-sarikaya-6lo-ap-nd-01.
I generally like the idea but still have some questions. I wonder what about
collisions for cryptographic IDs. The draft defines them as 64-bits long. I
assume that at a minimum 80 bits are needed to assume that it is collision
free. Or is it the case that collisions are not an issue in this case?
I just ran some numbers through for another problem with a 64bit number field.
It works out as follows.
The formula is: 1 - e^{-k^2/(2n)}
Where n is your maximum popluation size (2^64 here, 1.84E19) and K is your
actual population.
A .01% probablity of a collision is a bit less than 66M devices.
If everyone in the world has one device (7B), then you are up to a 73%
probablity of a collision.
So your risk of a collision on a network is there, but really low.
ID author, you may want to put this formula into your draft.
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