Hot Plug and How to Defeat It

Finally I found the URL of a device I’ve been hearing rumours about. The HotPlug is a device to allow you to move a computer without turning it off [1]. It is described as being created for “Government/Forensic customers” but is also being advertised for moving servers without powering them down.

The primary way that it works is by slightly unplugging the power plug and connecting wires to the active and neutral terminals, then when mains power is no longer connected it supplies power from a UPS. When mains power is re-connected the UPS is cut off.

Australian 240 volt 10 amp mains power plug

Modern electrical safety standards in most countries require that exposed pins of a power plug (other than the earth) be shielded to prevent metal objects or the fingers of young children from touching live conductors. The image above shows a recent Australian power plug which has the active and neutral pins protected with plastic such that if the plug is slightly removed there will be no access to live conductors. I have photographed it resting on a keyboard so that people who aren’t familiar with Australian plugs can see the approximate scale.

I’m not sure exactly when the new safer plugs were introduced, a mobile phone I bought just over three years ago has the old-style plug (no shielding) while most things that I bought since then have it. In any case I expect that a good number of PCs being used by Australian companies have the old style as I expect that some machines with the older plugs haven’t reached their three year tax write-down period.

For a device which has a plug with such shielding they sell kits for disassembling the power lead or taking the power point from the wall. I spoke to an an electrician who assured me that he could with a 100% success rate attach to wires within a power cord without any special tools (saving $149 of equipment that the HotPlug people offer). Any of these things will need to be implemented by a qualified electrician to be legal, and any electrician who has been doing the job for a while probably has a lot of experience working before the recent safety concerns about “working live“.

The part of the web site which concerns moving servers seems a little weak. It seems to be based on the idea that someone might have servers which don’t have redundant PSUs (IE really cheap machines – maybe re-purposed desktop machines) which have to be moved without any down-time and for which spending $500US on a device to cut the power (plus extra money to pay an electrician to use it) is considered a good investment. The only customers I can imagine for such a device are criminals and cops.

I also wonder whether you could get the same result with a simple switch that cuts from one power source to another. I find that it’s not uncommon for brief power fluctuations to cause the lights to flicker but for most desktop machines to not reboot. So obviously the capacitors in the PSU and on the motherboard can keep things running for a small amount of time without mains power. That should be enough for the power to be switched across to another source. It probably wouldn’t be as reliable but a “non-government” organisation which desires the use of such devices probably doesn’t want any evidence that they ever purchased one…

Now given that such devices are out there, the question is how to work around them. One thing that they advertise is “mouse jigglers” to prevent screen-lock programs from activating. So an obvious first step is to not allow jiggling to prevent the screen-saver. Forcing people to re-authenticate periodically during their work is not going to impact productivity much (of course the down-side is that it offers more opportunities for shoulder-surfing authentication methods).

Once a machine is taken the next step is to delay or prevent an attacker from reading the data. If an attacker has the resources of a major government behind them then they could read the bus of the machine to extract data and maybe isolate the CPU and send memory read commands to system memory to extract all data (including the keys for decrypting the hard drive). The only possible defence against that would be to have multiple machines exchanging encrypted heart-beat packets and configured to immediately shut themselves down if all other machines stop sending packets to them. But if defending against an attacker with more modest resources the shutdown period could be a lot longer (maybe a week without a successful login).

Obviously an attacker who gets physical ownership of a running machine will try and crack it. This is where all the OS security features we know can be used to delay them long enough to allow an automated shut-down that will remove the encryption keys from memory.

4 comments to Hot Plug and How to Defeat It

  • Matthew W. S. Bell

    Er, I looked at the videos on the website, and the method you described is not referenced at all…

  • etbe

    Matthew: I didn’t view the videos, just read the text. I generally avoid videos as they always seem to be in painful and annoying formats and the content is never as clear or easy to quote as text.

  • Jaakko Niemi

    A lot of network gear and low end servers have only one PSU.

    You’d be suprised how many. There are people who consider network gear as nuisance.

  • etbe

    Jaakko: I realise the quantity of equipment without redundant PSUs. My claim is that people are unlikely to purchase such cheap servers and then purchase expensive equipment (and pay electricians) to move it. As for network gear, it generally boots quickly so a significant amount of the down-time taken for a move is likely to be moving the network connections.