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 文章标题 : [新闻]BitLocker被princeton的 hacker破解,有论文或视频为证
帖子发表于 : 2008-02-22 15:40 
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It's an old adage that no security measure is worth anything if an attacker has physical access to the machine, but things like heavy-duty disk encryption are supposed to at least slow things down. Sadly, that may not actually be the case, as a group of Princeton researchers has just published a paper detailing an exploit that requires little more than a spray duster and a screwdriver. Since the encryption key for systems like BitLocker and FileVault lives in RAM, all an attacker has to do to get it is cool the RAM modules with the air duster held upside down, yank the DIMM, and insert it into another machine, where it can then be read to access the key. Of course, this assumes that you've already typed in your password, but check the video after the break to see how long bits in RAM stay written -- even if you've turned off your computer, there's a chance the key can still be read. Looks like there's an actual benefit to MacBook Air's soldered-in RAM after all, eh?


理论基础为内存掉电后,数据并没有
丢失!

http://citp.princeton.edu/memory/


引用:
Abstract Contrary to popular assumption, DRAMs used in most modern computers retain their contents for seconds to minutes after power is lost, even at operating temperatures and even if removed from a motherboard. Although DRAMs become less reliable when they are not refreshed, they are not immediately erased, and their contents persist sufficiently for malicious (or forensic) acquisition of usable full-system memory images. We show that this phenomenon limits the ability of an operating system to protect cryptographic key material from an attacker with physical access. We use cold reboots to mount attacks on popular disk encryption systems — BitLocker, FileVault, dm-crypt, and TrueCrypt — using no special devices or materials. We experimentally characterize the extent and predictability of memory remanence and report that remanence times can be increased dramatically with simple techniques. We offer new algorithms for finding cryptographic keys in memory images and for correcting errors caused by bit decay. Though we discuss several strategies for partially mitigating these risks, we know of no simple remedy that would eliminate them.


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帖子发表于 : 2008-02-22 16:15 
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引用:
We found that information in most computers’ RAMs will persist from several seconds to a minute even at room temperature. We also found a cheap and widely available product — “canned air” spray dusters — can be used to produce temperatures cold enough to make RAM contents last for a long time even when the memory chips are physically removed from the computer. The other components of our attack are easy to automate and require nothing more unusual than a laptop and an Ethernet cable, or a USB Flash drive. With only these supplies, someone could carry out our attacks against a target computer in a matter of minutes.


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帖子发表于 : 2008-02-22 16:16 
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New Research Result: Cold Boot Attacks on Disk Encryption
February 21st, 2008 by Ed Felten

Today eight colleagues and I are releasing a significant new research result. We show that disk encryption, the standard approach to protecting sensitive data on laptops, can be defeated by relatively simple methods. We demonstrate our methods by using them to defeat three popular disk encryption products: BitLocker, which comes with Windows Vista; FileVault, which comes with MacOS X; and dm-crypt, which is used with Linux. The research team includes J. Alex Halderman, Seth D. Schoen, Nadia Heninger, William Clarkson, William Paul, Joseph A. Calandrino, Ariel J. Feldman, Jacob Appelbaum, and Edward W. Felten.

Our site has links to the paper, an explanatory video, and other materials.

The root of the problem lies in an unexpected property of today’s DRAM memories. DRAMs are the main memory chips used to store data while the system is running. Virtually everybody, including experts, will tell you that DRAM contents are lost when you turn off the power. But this isn’t so. Our research shows that data in DRAM actually fades out gradually over a period of seconds to minutes, enabling an attacker to read the full contents of memory by cutting power and then rebooting into a malicious operating system.

Interestingly, if you cool the DRAM chips, for example by spraying inverted cans of “canned air” dusting spray on them, the chips will retain their contents for much longer. At these temperatures (around -50 °C) you can remove the chips from the computer and let them sit on the table for ten minutes or more, without appreciable loss of data. Cool the chips in liquid nitrogen (-196 °C) and they hold their state for hours at least, without any power. Just put the chips back into a machine and you can read out their contents.

This is deadly for disk encryption products because they rely on keeping master decryption keys in DRAM. This was thought to be safe because the operating system would keep any malicious programs from accessing the keys in memory, and there was no way to get rid of the operating system without cutting power to the machine, which “everybody knew” would cause the keys to be erased.

Our results show that an attacker can cut power to the computer, then power it back up and boot a malicious operating system (from, say, a thumb drive) that copies the contents of memory. Having done that, the attacker can search through the captured memory contents, find any crypto keys that might be there, and use them to start decrypting hard disk contents. We show very effective methods for finding and extracting keys from memory, even if the contents of memory have faded somewhat (i.e., even if some bits of memory were flipped during the power-off interval). If the attacker is worried that memory will fade too quickly, he can chill the DRAM chips before cutting power.

There seems to be no easy fix for these problems. Fundamentally, disk encryption programs now have nowhere safe to store their keys. Today’s Trusted Computing hardware does not seem to help; for example, we can defeat BitLocker despite its use of a Trusted Platform Module.

For more details, see the paper site.


http://citp.princeton.edu/memory/


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帖子发表于 : 2008-02-22 16:17 
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Experimenting with Memory Remanence


Advanced users can try to observe memory remanence effects on their own systems by performing this simple experiment. (These instructions are written for Linux machines, but they can be adapted for other operating systems.)

1. Create a Python program with the following code:

#!/usr/bin/env python

# a pirate's favorite chemical element
a = ""
while 1: a += "ARGON"

This program will fill memory with copies of the word “ARGON”.
2. Run the sync command to flush any cached data to the hard disk.

3. Start the Python program, and allow it to run for several minutes. It won’t display anything on the screen, but after a while you should see hard drive activity as the memory fills and data gets swapped to disk.

4. Deliberately crash the system by turning the power off and on again or briefly removing the battery and power cord.

5. After the system reboots, look for the “ARGON” pattern in memory. You can use the following command to print strings of text contained in RAM:

sudo strings /dev/mem | less

If you see copies of the string “ARGON”, some of the contents of memory survived the reboot. You’ll see many other strings that were loaded into memory when the system restarted, and possibly other data left over from before it rebooted.

If you don’t see any copies of the pattern, possible explanations include (1) you have ECC (error-correcting) RAM, which the BIOS clears at boot; (2) your BIOS clears RAM at boot for another reason (try disabling the memory test or enabling “Quick Boot” mode); (3) your RAM’s retention time is too short to be noticeable at normal temperatures. In any case, your computer might still be vulnerable — an attacker could cool the RAM so that the data takes longer to decay and/or transfer the memory modules to a computer that doesn’t clear RAM at boot and read them there.


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帖子发表于 : 2008-02-22 16:32 
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Data remanence


Data remanence is the residual representation of data that has been in some way been nominally erased or removed. This residue may be due to data being left intact by a nominal delete operation, or through physical properties of the storage medium. Data remanence may make inadvertent disclosure of sensitive information possible, should the storage media be released into an uncontrolled environment (e.g., thrown in the trash, or given to a third-party).

Over time, various techniques have been developed to counter data remanence. Depending on the effectiveness and intent, they are often classified as either clearing or purging/sanitizing. Specific methods include overwriting, degaussing, encryption, and physical destruction.

Many operating systems, file managers, and other software provide a facility where file are not immediately deleted when the user requests that action. Instead, the file is moved to a holding area, to allow the user to easily revert a mistake.

Even when an explicit deleted file retention facility is not provided or when the user does not use it, most computers do not actually remove the contents of a file when it is deleted. Instead, they simply remove the file's entry from the file system directory. The contents of the file -- the actual data -- remain on the storage medium. The data will remain there until the operating system reuses the space for new data. In some systems, enough filesystem metadata is also left behind to enable easy undeletion by commonly available utility software. Even when undelete is not possible, until the actual data is overwritten, it can be read by software that reads disk sectors directly. Computer forensics often employs such software.

Likewise, reformatting, repartitioning or reimaging a system is not always guaranteed to write to every area of the disk, though all will cause the disk to appear empty to most software.

Finally, even when the storage medium is overwritten, physical properties of the medium may make it possible to recover the previous contents using laboratory techniques.

Countermeasures

Clearing

Clearing is the removal of sensitive data from storage devices in such a way that there is assurance, proportional to the sensitivity of the data, that the data may not be reconstructed using normal system functions. The data may still be recoverable, but not without unusual effort.

Clearing is typically considered an administrative protection against accidental disclosure within an organization. For example, before a floppy disk is re-used within an organization, its contents may be cleared to prevent their accidental disclosure to the next user.

Purging

Purging or sanitizing is the removal of sensitive data from a system or storage device with the intent that the data can not be reconstructed by any known technique. Purging is generally done before releasing media outside of control, such as before discarding old media, or moving media to a computer with different security requirements.

Specific methods

Overwriting

A common method used to counter data remanence is to overwrite the storage medium with new data. This is often called a wiping or shredding a file or disk. Because such methods can often be implemented in software alone, and may be able to selectively target only part of a medium, it is a popular, low-cost option for some applications.

The simplest overwrite technique writes the same data everywhere -- often just a pattern of all zeros. At a minimum, this will prevent the data from being retrieved simply by reading from the medium again, and thus is often used for clearing.

To counter more advanced data recovery techniques, specific overwrite patterns are often prescribed. These may be generic patterns intended to eradicate any trace signatures. For example, writing repeated, alternating patterns of ones and zeros may be more effective than zeros alone. Patterns based on the existing data may also be used, such as the complement, or bitwise inverse or NOT, of the existing data. For example, if the existing data is 1101 0110, its complement would be 0010 1001. Combinations of patterns are frequently specified.

One challenge with an overwrite is that some areas of the disk may be inaccessible, due to media degradation or other errors. Software overwrite may also be problematic in high-security environments which require stronger controls on data commingling than can be provided by the software in use. The use of advanced storage technologies may also make file-based overwrite ineffective.

As of Nov 2007, overwriting is no longer a DoD-acceptable sanitization method for magnetic media. Only degaussing or physical destruction is acceptable.[1]

Gutmann method

Peter Gutmann investigated data recovery from nominally overwritten media in the mid-1990s. He suggested magnetic force microscopy may be able to recover such data, and developed specific patterns, for specific drive technologies, designed to counter such.[2] These patterns have come to be known as the Gutmann method.

Daniel Feenberg, an economist at the private National Bureau of Economic Research, claims that the chances of overwritten data being recovered from a modern hard drive amount to "urban legend".[3]

Degaussing

Degaussing is the removal or reduction of a magnetic field. Applied to magnetic media, degaussing may purge an entire media element quickly and effectively. A device, called a degausser, designed for the media being erased, is used.

Degaussing often renders hard disks inoperable, as it erases low-level formatting which is only done at the factory, during manufacture. Degaussed floppy disks can generally be reformatted and reused.

In high-security environments, one may be required to use a degausser which has been approved for the task. For example, in US government and military jurisdictions, one may be required to use a degausser from the NSA's "Evaluated Products List" [4].

Encryption

Encrypting data before it is stored on the medium may mitigate concerns about data remanence. If the decryption key is strong and carefully controlled (i.e., not itself subject to data remanence), it may effectively make any data on the medium unrecoverable. Even if the key is stored on the medium, it may prove easier or quicker to overwrite just the key, vs the entire disk.

Encryption may be done on a file-by-file basis, or on the whole disk.

Physical destruction
Data destruction can be contracted out
Data destruction can be contracted out

Physical destruction of the data storage medium is generally considered the most certain way to counter data remanence, although also at the highest cost. Not only is the process generally time-consuming and cumbersome, it obviously renders the media unusable. Further, with the high recording densities of modern media, even a small media fragment may contain large amounts of data.

Specific destruction techniques include:

* Physically breaking the media apart, by grinding, shredding, etc.
* Incinerating
* Phase transition (i.e., liquification or vaporization of a solid disk)
* Application of corrosive chemicals, such as acids, to recording surfaces
* For magnetic media, raising its temperature above the Curie point

Complications

Inaccessible media areas

Storage media may have areas which become inaccessible by normal means. For example, a magnetic disks may develop new "bad sectors" after data has been written, and tapes require inter-record gaps. Modern hard disks often feature automatic remapping of marginal sectors or tracks, which the OS may not even be aware of. Attempts to counter data remanence by overwriting may not be successful in such situations, as data remnants may persist in such nominally inaccessible areas.

Advanced storage systems

Data storage systems with more sophisticated features may make overwrite ineffective, especially on a per-file basis.

Journaling file systems increase the integrity of data by recording write operations in multiple locations, and applying transaction-like semantics. On such systems, data remnants may exist in locations "outside" the nominal file storage location.

Some file systems implement copy-on-write or built-in revision control, with the intent that writing to a file never overwrites data in-place.

Technologies such as RAID and anti-fragmentation techniques may result in file data being written to multiple locations, either by design (for fault tolerance), or as data remnants.

Optical media

Optical media are not magnetic and are not affected by degaussing. Write-once optical media (CD-R, DVD-R, etc.) also cannot be purged by overwrite. Read/write optical media, such as CD-RW and DVD-RW, may be receptive to overwriting.

Data in RAM

Data remanence has been observed in static RAM, which is typically considered volatile (i.e., contents are erased with loss of electrical power). In the study, data retention was sometimes observed even at room temperature.[5]

Another study found data remanence in dynamic random access memory (DRAM), again with data retention of seconds to minutes at room temperature and much longer times when memory chips were cooled to low temperature. The study authors were able to recover cryptographic keys for several popular disk encryption systems despite some memory degradation by taking advantage of redundancy in the way keys are stored after they have been expanded for efficient use, such as in key scheduling. The authors recommend that computers be powered down, rather than be left in a "sleep" state, when not in physical control of the owner. [6]

Standards

* US DoD DoD 5220.22-M: National Industrial Security Program Operating Manual (NISPOM)
o Current editions no longer specify specific sanitization methods. Standards for sanitization are left up to the Cognizant Security Authority.[7]
o Past editions (1995) explicitly gave sanitization methods.[8]
o The Defense Security Service provides a Clearing and Sanitization Matrix (C&SM) which does specify methods[1].
o As of the Nov 2007 edition of the DSS C&SM, overwriting is no longer acceptable for sanitization of magnetic media. Only degaussing (with an NSA approved degausser) or physical destruction is acceptable.
* NAVSO P5239-26 standards are more rigorous versions of the same procedure[clarify].
* US NIST Special Publication 800-88: Guidelines for Media Sanitization[9]
* RCMP G2-003: Hard Drive Secure Information Removal and Destruction Guidelines[10]
o Up to A/B/Confidential data: Triple overwrite using RCMP DSX software
o C/Secret/Top Secret data: Physical destruction or degaussing


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帖子发表于 : 2008-02-22 16:36 
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Zeroisation



In cryptography, zeroisation (also spelled zeroization) is the practice of erasing sensitive parameters (especially keys) from a cryptographic module to prevent their disclosure if the equipment is captured. When encryption was performed by mechanical devices, this would often mean changing all the machine's settings to some fixed, meaningless value, such as zero. On machines with letter settings rather than numerals, the letter 'O' was often used instead. Some machines had a button or lever for performing this process in a single step. Zeroisation would typically be performed at the end of an encryption session to prevent accidental disclosure of the keys, or immediately when there was a risk of capture by an adversary.

In modern software based cryptographic modules, zeroisation is made considerably more complex by issues such as virtual memory and compiler optimisations. Also, zeroisation may need to be applied not only to the key, but also to a plaintext and some intermediate values. A cryptographic software developer must have an intimate understanding of memory management in a machine, and be prepared to zeroise data whenever a sensitive location might move outside the security boundary. Typically this will involve overwriting the data with zeroes, but in the case of some types of non-volatile storage the process is much more complex; see data remanence.

As well as zeroising data due to memory management, software designers consider performing zeroisation:

* When an application changes mode (e.g. to a test mode) or user;
* When a computer process changes privileges;
* On termination (including abnormal termination);
* On any error condition which may indicate instability or tampering;
* Upon user request;
* Immediately, the last time the parameter is required; and
* Possibly if a parameter has not been required for some time.

Informally, software developers may also use zeroise to mean any overwriting of sensitive data, not necessarily of a cryptographic nature.

In tamper resistant hardware, automatic zeroisation may be initiated when tampering is detected. Such hardware may be rated for cold zeroisation, the ability to zeroise itself without its normal power supply enabled.

Standards for zeroisation are specified in ANSI X9.17 and FIPS 140-2.
Retrieved from "http://en.wikipedia.org/wiki/Zeroisation"

Categories: Key management


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帖子发表于 : 2008-02-22 16:41 
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http://www.madisonlinux.org/pipermail/m ... 07261.html


On Wed, Oct 29, 2003 at 08:24:46AM -0800, Darrick Hartman wrote:
> Thank you to everyone who replied...including the
> numerous people who obviously love this dban project.
>
> My hard drive does not function properly. It has bad
> sectors which prevent me from writing to it. It is

If the drive still powers up you can probably run a
low level formatter on it and get access to 99% of the
sectors. Once you have a cleaner format you can run
your DBAN or whatever on it and be sure that the sectors
that weren't corrupted are now wiped fairly clean.

Which formatter you'll use depends on the manufacturer.
IBM/Hitachi would use IBM's Drive Fitness Test program, ex.


> covered by warranty. Unfortunately, I cannot affect
> the data on the disk with any other method than a
> magnet and still send it back for warranty
> replacement. (I thought I could, but the drive is
> "more deader" than I thought.

Give the low level format a try before you give up.


> While it is intriguing, I don't think that the
> reseller would appreciate my sanding skills on the
> plattens. If I really really just wanted to kill the
> drive, I would put it through one of our high
> temperature furnaces (oh 2500F should do it) or
> chemically dissolve it in some nasty acid. That's not
> the case.

You could always ask them if it's permissable to trash the
drive, as you have your banking records on it. Can't hurt....


> Darrick




Indeed, very little on disk drives is proof against someone who
dismantles it and runs a scanning electron microscope over it to
analyze the remnant magnetism. One pass with zero's will defend you
against casual snoopers. A few passes of varying data will defend you
against anyone with a smaller budget than the NSA.

Note that the sufficiently well funded can play analagous games with
semiconductor memory; if you store data in RAM for a long time there
are ways of analyzing the chips to deduce a lot of it too. Paranoid yet?

Degaussing magnets are pretty much a lost cause, sorry. The
coercivity of modern disk and tape media is so high that pretty much
no one outside a fusion research lab has magnets (usually
superconducting) strong enough to do the job.

To keep people from reading your data, you need either encryption,
multiple erasure passes, or thorough physical destruction.

Have been for a while :)

Note, too, that getting the RAM very cold (e.g., a liquid nitrogen bath)
quickly after shutdown should allow it to keep its state for quite
some time after the power button goes off(certainly long enough to get it
to the lab).

Also, this is a good point for people who use encrypted file systems.
Likely, the key will be stored in memory, probably in the same location,
for quite some time. It'd be nice if the crypto kernel drivers would hook
into the VM code and change the physical memory address in the relevent
memory pages on a regular basis (not sure if it does already).

So, what would it take to protect the contents of your RAM from everyone
but the NSA? Sounds like this might be as much of a challenge.

Just a thought...


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帖子发表于 : 2008-02-22 18:09 
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TPM也保不了? :shock:


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帖子发表于 : 2008-02-22 23:40 
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如果ee来了,肯定说打倒不翻译的 :)
这蝌蚪文,看不懂哦


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饶了我吧。满屏的蝌蚪文,看得头痛


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帖子发表于 : 2008-04-03 9:48 
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不知道在说什么


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