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Microsoft Responds to Windows BitLocker Claims

In a posting at the Windows Security Blog, Microsoft's Paul Cooke addresses recent claims by Fraunhofer SIT about the supposed ineffectiveness of BitLocker, the full disk encryption technology that's available in Windows Vista, 7, and Server 2008. According to the software giant, the Fraunhofer SIT report is incorrect: BitLocker can not be "broken" or "bypassed" when used as directed. Here's the word:

Windows 7 is seeing success in the marketplace which I am very happy about from a security perspective. The Microsoft Security Intelligence Report has shown us again and again that the more up-to-date a PC is, the less likely it is to be infected by malware and other potentially dangerous software. So Windows 7 making strides is helpful to the ecosystem overall from a security standpoint. Success comes at a price though, through greater scrutiny and misinterpretation of some of the technologies. One of those technologies is BitLocker.

I've seen numerous claims the past few weeks about weaknesses in BitLocker and even claims of commercial software that "breaks" BitLocker. One claim is from a product that "allows bypassing BitLocker encryption for seized computers." This claim is for a forensics product and has legitimate uses; however, to say it "breaks" BitLocker is a bit of a misnomer. The tool "recovers encryption keys for hard drives" which relies on the assumption that a physical image of memory is accessible, which is not the case if you follow BitLocker's best practices guidance. The product, like others used legitimately for data recovery and digital forensics analysis, requires "a physical memory image file of the target computer" to extract the encryption keys for a BitLocker disk.  Our discussions of Windows BitLocker have always been to communicate that it is intended to help protect data at rest (e.g. when the machine is powered off). If a forensics analyst or thief/adversary has physical access to a running system, it may be possible to make a copy of the computer's memory contents by using an administrative account on the system, or potentially through hardware-based methods such as direct memory access (DMA).

Another report discusses targeted attack vectors where the attacker must gain physical access to the computer, multiple times I might add. This research is similar to other published attacks where the owner leaves a computer unattended in a hotel room and anyone with access to the room could tamper with this computer. This sort of targeted attack poses a relatively low risk to folks who use BitLocker in the real world.Even with BitLocker's multi-authentication configurations, an attacker could spoof the pre-OS collection of the user's PIN, store this PIN for later retrieval, and then reboot into the authentic collection of the user's PIN. The attacker would then be required to gain physical access to the laptop for a second time in order to retrieve the user's PIN and complete the attack scheme. These sorts of targeted threats are not new and are something we've addressed in the past; in 2006 we discussed similar attacks, where we've been straightforward with customers and partners that BitLocker does not protect against these unlikely, targeted attacks.

Our customers are confronted with a wide spectrum of data security threats that are specific to their environment and we work hard to provide capabilities and information to help the customer achieve the right balance of security, manageability, and ease-of-use for their specific circumstances. BitLocker is an effective solution to help safeguard personal and private data on mobile PCs and provides a number of protection options that meet different end-user needs.  Like most full volume encryption products on the market, BitLocker uses a key-in memory when the system is running in order to encrypt/decrypt data on the fly for the drives in use.  Also like other encryption products, a determined adversary has significant advantages when they have physical access to a computer.

We recognize users want advice with regards to BitLocker and have published best practice guidance in The Data Encryption Toolkit for Mobile PCs. In the toolkit, we discuss the balance of security and usability and detail that the most secure method to use BitLocker in hibernate mode and a TPM+PIN configuration. Using this method, a machine that is powered off or hibernated will protect users from the ability to extract a physical memory image of the computer.

Windows 7 BitLocker continues to be a foundational component adding to any defense in depth strategy for securing systems, and specifically laptops.  Even with the great enhancements made in Windows 7 such as BitLocker To Go, it still remains that BitLocker alone is not a complete security solution.  IT professionals as well as users must be diligent when protecting IT resources and the best protection against these sorts of targeted attacks requires more than just technology: it requires end user education and physical security also play important roles.

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