Re: [6tsch] draft-ohba-6tsch-security-00

[Jonathan Simon <[e-mail]>]

Section 1

"6TSCH builds on a series of semi-proprietary wireless protocols..."
Is it really relevant that TSCH was built on concepts in WirelessHART?  TSCH is not proprietary, and saying it builds on proprietary protocols is a red flag.

"Following Metcalf's law..."
Not only is it not clear what point is being made, Metcalf’s law measures “utility” in connections.  For a networked sensor device, there are likely a finite number of consumers of its data, and the total number of nodes is an irrelevant utility metric. Additionally, in terms of mesh connectivity, in general there is little additional utility to having 1000 neighbors (which may be more than the node can store) over 100, and perhaps 100 over 10 provided there is sufficient connectivity for the network to function.

General

So the problem this draft is trying to solve is shared link-layer keys in the network.  It does this by proposing an 3-phase authentication scheme with unstated overhead to provide unique per-peer link-layer keys, among other things.

a) Each node would need to be preconfigured with every node's certificate material (bad), or communicate with the coordinator to validate PK certs for every device attempting to join (nearly as bad if this takes a lot of packets).  Without seeing the overhead, its hard to tell if this would even work - if a device has to stay synchronized for a long time using unsecured frames, how is that any better than a shared secret? There's still a DoS vector in the unsecured bandwidth.

b) I agree that in protocols with a well-known key for authenticating join requests, an attacker can perform a DoS attack by simulating many devices joining.  These messages are passed up to the coordinator (and rejected).  However this requires distributed injection of messages to be maximally effective, and this is little worse than flooding the network with packets authenticated with the wrong key, so I don't see how per-peer keys is an effective DoS mitigator.
-- 
Jonathan Simon, Ph. D
Director of Systems Engineering
Linear Technology, Dust Networks product group
30695 Huntwood Ave
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On Jun 23, 2013, at 7:10 PM, <[e-mail]> <[e-mail]> wrote:

> 6tsch-security draft has been submitted to IETF:
> 
> http://tools.ietf.org/html/draft-ohba-6tsch-security-00
> 
> Regards,
> Yoshihiro Ohba
> 
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