Don’t Panic, Your Data Is Secure
Researchers at Princeton University announced last week that they could, under certain conditions, retrieve data from a computer’s memory even though it had been turned off. The announcement was made based on a new paper from the research group led by Princeton’s Ed Felten, described in the researchers’ blog and more completely described by a technical paper and a video demonstration.
Various computer news sites covered the same story; all discuss how this could be used to get at data people may have thought was secured by encryption. This concerns a lot of computer security people, for good reason, but it’s now been picked up by the New York Times, with the headline “Researchers Find Way to Steal Encrypted Data”.
Before the panic attacks start, let’s look at what really has been demonstrated. Then, at least if we panic, we’ll know why. To understand this whole discussion, we need to talk a little bit about computers. Since you’re reading this on a computer, you probably already know that computers have, among other things, disk memory and RAM memory. The disk is relatively slow, and stores data for a long time in a stable form (at least until the disk hardware fails and the disk “crashes”.)
Computers and Disk Encryption
Modern laptop computers have many hundreds of gigabytes worth of data space available on their hard drives, which means room for hundreds of thousands, or millions, of pages of text. This makes them very convenient to use, but it also means that any user might be carrying around information worth millions of dollars — anything from a writer’s new blockbuster exposé, to records on tens of thousands of veterans, to the terrorist’s secret plans to blow up Disneyland. If
the laptop is lost, and the data on the drive can be retrieved, the perpetrators may get away, the veterans might have their identities stolen, the terrorists might be foiled.
Of course, we all want the terrorists foiled, but we might not want anyone to be able to find our notes for the blockbuster, or the veterans’ Social Security numbers. So there are a variety of products around called “disk encryptors” that use an encryption, a mathematical code, to make the data unreadable unless you have the special password, or “key.” If you don’t have the key, the data on the disk is meaningless, gibberish; if you have the key, it’s readable.
Computers, including the your laptop, have a second kind of memory call RAM (for “random access memory”.) RAM memory is fast, not as stable, and is used essentially for the working memory, the ‘scratchpad” that your running programs need. In fact, in most computers, this memory is what is called dynamic RAM, which just means the computer has to refresh the memory every so often; in fact,
it’s refreshed thousands of times a second, transparently. You never know about it, nor do you need to; since it’s dynamic, the usual understanding is that once the power is off and the refresh cycle stops, the data in DRAM is lost.
When you use an encryption program for your disk, normally has to be in memory so the disk’s data can be read. When you use a disk encryption program, like TruCrypt for Windows or FileVault on a Mac, you have to enter the key in order to read the data, and that means the key is sitting somewhere in the computers DRAM while you’re using it.
Most users don’t know or care. (Government agencies are different; a computer handling top secret information is protected in various overt and subtle ways. But they’re not most users.) Users who do care have depended on the fact that their key disappears when the power shuts off. And here endeth the expository lump.
Cracking the Code
What Felten’s group showed was that these keys in DRAM don’t disappear instantly. There is a short time after the power is turned off in which you can recover data from the DRAM memory; if that includes the keys you need to read the disk, then the disk is compromised too. What’s more, by chilling the DRAM, you can extend the time it takes for the data to be lost: chill it to -50º C (about -58º F) and it can last for much longer; chill it with easily available liquid nitrogen to -196º C (-320º F) and it can be read for hours. Then Felten’s group demonstrated that by chilling the chips in a computer that used a commercial disk encryption product, they had plenty of time to use a small software tool called “UnBitLocker” to capture the keys, which let them read the encrypted data off the disk.
What it Means
Obviously, if you don’t turn the power off, it’s even worse: if you’re in the habit of carrying around your laptop in “sleep” or “suspend” mode, or using an “instant on” function, there is always the chance that someone could steal your laptop, extract your keys, read your data, and do bad things with it. If you are a little more wary and you were depending on power off to save you from having your keys taken, you need to think about this — but how much of a risk is it really?
I suggest not much. While it’s true that this could be used to get at encrypted data, let’s think about what it takes to do it. First of all, at normal operating temperatures according to the paper, data persists in DRAM for roughly between three and thirty seconds, and the fancier and more recent your computer is, the faster the data disappears. So long as you shut down your computer, within a minute or so, you’re safe from this attack. (You’re not, of course, safe from someone holding a gun to your head and saying “give me the key,” which would be a more common attack anyway.)
If the computer still has power, then to make use of this attack, the attacker must first get the computer away from you without shutting it off, then use the UnBitLocker software to find the keys. If they’re not going to be able to do that immediately, they can chill the computer with a cold spray, or even liquid nitrogen, and take their time. But they have to be technically sophisticated, know what computer to steal, and know how to apply this technique, in order to use it. That’s a lot of work, and pretty specialized thieves.
That kind of specialized, sophisticated thief certainly exists: they’re called “spies”. This is why TOP SECRET information is supposed to be more protected, in specialized containers, secured behind locked doors. James Bond and Jack Bauer could pull it off; TOP SECRET information can be worth this kind of effort, and a lot more.
Personal data, not so much.
The real lesson here is that if you’re worried enough about your data to use a disk encryption product, you shouldn’t leave the power on to your computer when you don’t need to. Turn the power off, and a minute later you’re safe from any but the most sophisticated attack, or the most brutally unsophisticated.
Charlie Martin is a Colorado computer scientist and nearly-successful screenwriter who contributes to the Flares Into Darkness political blog as ‘Seneca the Younger,’ and blogs under his own name at the aggressively non-political Explorations blog.
The issue is not how easy or how difficult it is to gather the encryption key from RAM. The issue is that the encryption key is exposed in the system where it can be collected by freezing the RAM or with malicous software.
The demonstrated hack would theoretically and practically not be possible with hard disk embeddedd dosk encryption as shipped by Dell, Lenovo, ASI and NEC-Europe.
The issue is that today’s common PC architecture is inherently unsafe. The hack only demonstarted that that.
And the issue is not limited to software based encryption tools. It also applies to i.e. VPN keys that are stored on the hard disk making an enterprise subject to malintended intrusion.
In the end it is all about protection of property and that can not be accomplished if the world does not turn on the Trusted Computing Group’s Trusted Platform Module (TPM) that has shipped in over 150 million enterprise class PCs already.
It is time that the enterprises wake up, acquire the necessary TPM management tools that are available today (i.e from Dell, ASI and NEC-Europe) and turn on the TPMs they already have in their clients.
On an other point, big PC OEMs, like HP and others, do the consumer community a real disservice by not yet offering the TCG/TPM technology in cosumer grade platforms.
Taking into consideration that the lifespan of a consumer platform far exceeds that of an enterprise platforms consumers will have to replace their new PCs as soon as real world secure applications will be lit on the net; And I think we will start to see them within the next 12-18 months.
Andreas, I think you’re overstating this fairly radically. The underlying risk of this particular exploit is small: it requires sophisticated intervention in a fairly small time window, unless the machine is stolen and suborned with power still on. Solution: turn the power off.
Is this an issue for those of us working in the data-at-rest world, eg, IEEE 1619? You bet, but the implementations of encrypted data-at-rest very probably are vulnerable to memory-examination attacks if you can have unlimited access to a power-up machine. Solution: physical security, and when the physical security isn’t assured, turn the damn power off.
We regularly hear of hundreds of unencrypted tapes being lost, and laptops full of millions of records of customer-identifying information en clair on their hard drives going missing. Until that problem is eliminated, worrying about this vulnerability seems unnecessary.
So, at the end of the day, the data on your computer is just as secure as your car or any of your other stuff: If some thief really wants it and knows what to do to get it, he will, regardless of how well you protect it. Fortunately most thieves don’t fit the above description; they just look for the easy marks.
In other words, I concur with Mr. Martin; there’s nothing new here.
I wouldn’t go that far, Joshua — Felten’s guys showed that this vulnerability exists and CAN be exploited. It’s just not as earthshaking as the Times makes it sound.
Most new computers are powered on with full remote access to memory (and disk if you are clever) even if they are turned off.
John, I know you said that over on Explorations as well; it’s certainly not true for laptops, and I don’t think it’s true of a lot of the server class machines with which I’m familiar. can you point me to an example of what you’re thinking about?
examples:
Many (if not all) servers from INTEL, IBM, HP, DELL, APPLE, and all new TYAN Motherboards:
http://www.intel.com/business/business-pc/manageability.htm?cid=cim:ggl|pro_us_manageability|k94F2|s
http://www.dell.com/downloads/global/products/pedge/en/pe_1950_III_spec_sheet.pdf
IPMI 2.0 http://www.intel.com/design/servers/ipmi/
Okay, John, how often do you carry a server as a laptop?
On IPMI machines, yes and no. IPMI equipped machine have a whole lot of potential vulnerabilities, but in general the IPMI functions are being handled by an ancillary processor. If you kill the power to the “server” part, there is no current to the memory. DRAM degradation applies. If it’s up, then you can generally explore the memory from the ancillary processor, but then you don’t need to freeze the chips either.
I have to agree with Charlie here. The Vulnerability does appear real and potentially high (it can end run any disk encryption solution which stores the key in RAM) but the opportunity for exploitation of the vulnerability (the Threat Level) seems quite low.
Servers, in most cases are mostly safe, since they should be securely locked away and any individual that would be in a position to kill the power, freeze the RAM and walk out should have been vetted long before they got to that room. Laptops are certianly a higher threat since they are often left free in the wild without additional measures. However, the attacker would still need to know (or strongly suspect) that the laptop was protected with Disk Encryption, before investing the time and work to freeze the RAM. There are a number of different ways to protect data at rest on a laptop. Disk encryption is only one of those options.
I would rate this as a Low Risk (Risk = Threat x Vulnerability) for Servers and a Low to Medium Risk for Laptops.
Additionally, if a company has very sensitive data which should not ever be exposed… it should NEVER be stored on media that leaves the protection of the corporate network (including zip/jump/thumb drives or laptops).