Michael StJohns <mstjo...@comcast.net> wrote: > On 7/27/2016 5:56 PM, Michael Richardson wrote:
> Kathleen Moriarty <kathleen.moriarty.i...@gmail.com> wrote: >>> Mohit Sethi <mohit.m.se...@ericsson.com> wrote: >>> > designed/developed/specified for their use-case. I could definitely >>> > see some IoT startup building a solution that switches on the lights >>> > in a room as soon as you unlock the door (thus keeping them in the >>> > same group). >>> >>> Or perhaps more usefully, turning the lights (and the oven) off when you >>> leave the house. >> Good points, but you could do this without them being in the same >> group with some controller that managed the interactions with each. >> This would be a good set of examples for the security considerations >> sections, providing guidance to use a controller rather than group >> keys to perform useful functions like these. mcr> I agree. mcr> Perhaps we could convince Mike St.Johns to write that section? msj> Probably not - as long as symmetric key group communications is used msj> as a control protocol. Well, who other than Nixon could go to China? mcr> And ACE has the right mechanisms to make this work well. msj> I agree - public key systems. But that seems to be out of scope here. I'm not convinced. What I have taken home is that people think they want to use symmetric keys, and perhaps it might be safe among completely equivalent devices. I take your point (strongly) that this bubble will be broken, with catastrophic results. We need asymmetric methods between bubbles, and we need to define that early. mcr> We should also consider whether we can use hash-chains, like S/KEY did, to mcr> authenticate messages that should only go out in emergencies. Such messages mcr> would clearly *need* to be multicast, but once used, they can never be mcr> reused. They can't be originated by more than one sender though.... so it's mcr> really the message stored by the "EMERGENCY STOP" button. msj> That's an interesting idea - but AIRC, hash chains could be originated msj> by anyone that held the signing/verification key. Yes, provided they distributed the initial (asymmetrically signed) h^n(k) value out in advance, and gave all the devices enough time to verify that signature. Plus flash to store the n-th hash. For the single sender/controller, multiple receiver/actuator situation this would be almost as fast as the symmetric group key, yet much more secure. For the multiple sender situation, you need to replicate things n-times. But it's still not n*m keys. msj> Let's do this the right way. Let's not bow to the "tyranny of the msj> light switch" in accepting solutions that are NOT secure, even for the msj> limited scope they are proposing. +1. -- Michael Richardson <mcr+i...@sandelman.ca>, Sandelman Software Works -= IPv6 IoT consulting =-
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