Remote Booting Using a Wireless Network Card?

Eboneye asks: "I have been assigned to a project to figure out how to make a diskless portable workstation (laptop) boot through a wireless connection. The idea is to have a stateless client that stores no local data (for security purposes). The only totally network boot stuff I have found uses PXE extensions. I have seen nothing like this in a PCMCIA card, much less a -wireless- PCMCIA card. For the proof of concept, we'll boot from a read only device, but of course during the setup phase use media to create a boot image on a boot server. I am currently looking at a couple different products that will provide a booting service. Ultimately, the goal is a to have a wireless tablet that can use different PCMCIA wireless adapters to connect to different LANs. Because of the specialized concerns of tablet PCs the solution has to be Windows compatible (sorry, Linux). Has anyone seen or worked on remote boot through wireless? Any experiences, gotchas, or suggestions for ways to solve this are welcome."

Comments

Don't bother

[duffbeer703]

You obviously haven't put enough thought into this.

A scheme like this, where you have to wait for a boot image to traverse a network, kinda defeats the purpose of tablet pcs.

If you are doing this for security, use applications that utilize strong encyrption. Playing games like this at the OS level is not the appropriate place to do this.

Serious security issues with 802.11b

[TheSHAD0W]

I strongly recommend you do NOT attempt this using the 802.11b protocol.

Let's assume you set up your wireless network PROPERLY; it has a gateway machine which restricts communications within your internal network, with that gateway being the only machine accessible to your wireless network. Your intent would be for your wireless machines to have nothing accessible, except to that gateway. Your remote machines would use an encrypted tunnel to log onto that gateway.

By remote-booting, you've destroyed that paradigm. A remotely-booting client would have no resources able to establish that encrypted tunnel, so you would not be able to boot through that gateway. Okay, fine, so let's say you put the boot image on the gateway machine outside the tunnel, or on a second server provided just for that purpose.

Now you have a brand new security hole... First off, an attacker doesn't need any security codes to grab a copy of your boot image; and that boot image, in order to establish your encrypted tunnels, would give the attacker, if not direct access to the gateway, at least valuable information narrowing down your security window. Having individual passwords users have to enter to log on might help things, but doesn't close the hole...

Since the link the booting PC would by definition be unencrypted, an attacker could spoof the wireless gateway for the period of time during when a wireless machine was booting, substituting a modified copy of the boot image. The result would be an insecure client, in which, if a password is entered, it could be forwarded to the attacker; or that machine might act as its own gateway, from the attacker through the insecure machine onto your network.

Re:Serious security issues with 802.11b

[addaon]

Precisely. You need some physical media for the encryption key, unless you're doing this entirely unencrypted, a decidedly bad idea. The way I would do this is to stick a 802.11 card, permanently, in each tablet, and issue people a usbkey storage device (www.usbkeydrive.com, for instance... pricier ones available). You could either give this to each employee, or have them check them out the same way they would have checked out a pc card under your plan. These keys are bootable in most machines (the advantage over using a pc card hard drive, which may or may not be bootable depending on your hardware); what you want to do is put on each a small bootable OS, the information necessary to form your VPN or however you're dealing with security, and nothing else. (At this point, you'll wish you could use linux, as it will require a smaller key, and be cheaper. But you'll survive with windows). Of course, there are still problems with this; you're not truly remote booting, just using a read-only boot disk. But it may be sufficient.

The next step up in complexity, as well as power, is to again use a usbkey to boot, but boot into linux. Have it boot from the read-only keychain, use the (unique) information on each key to establish the connection, etc, and then start X-Windows and rdesktop (linux remote desktop client), connecting to a remote windows server. It would be quite easy to secure the tablet so that the linux distribution is secure, and again you have a unique key to secure the connection. From the users point of view, they're working on a local windows machine, although from your point of view they're remotely logged on to another box.

These are just the first two ideas that came to mind. As the parent said, though, you need some kind of local storage for encrypted booting. I highly recommend a usbkey from one brand or another, as they're relatively cheap, absurdly robust, and quite convenient. And once you're allowing even a bit of storage, make it a useful amount, and boot locally off a secured disk, rather than trying to get the hardware to do something it's not supposed to do. Remote booting, keep in mind, just uses some ROM code to boot the computer and then moves control elsewhere. I'm pretty sure you won't find a system ROM or an 802.11 ROM that does what you need; instead, you're going to have to attach a boot ROM of some kind, and a usb key is about as good as it gets.

Oh, one final point, to make this make sense. Most of the usb keys have a read-only switch that can be latched, which makes them appear as read-only mass storage devices to the OS. Once you write the key, you can physically remove the switch (I've done this to several usb keys) to make it quite inconvenient to write to them again. It is possible to write to them either by opening them up and reconnecting the switch, or by writing a custom driver which ignores that the device is read-only (it turns out that, even in read-only mode, the keys I've worked with do honor writes), but neither of these methods is very convenient. It depends just how much security you need.