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Are there any known vulnerabilities to Ubuntu's full disk encryption feature?

I have some storage devices (thumbdrive and a few external hard drives used for backups) that I use with full disk encryption, so that if they're lost or stolen, my data can't be retrieved. Is this a false sense of security?

If someone were to obtain an encrypted drive, would it be possible for them to break the encryption, and if so, how long would it take?

EDIT: To clarify, I'm only asking about non-bootable drives. I'm aware of vulnerabilities to encrypted drives that are still used to boot the OS.

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What algorithm/program have you used to encrypt the disks? How secure is your password? –  BrownE Feb 8 '12 at 4:51
    
@BrownE, I've used Ubuntu's "Disk Utility" GUI as well as "cryptsetup" from the command line. My password's about two dozen characters, so fairly secure. –  Cerin Feb 8 '12 at 14:37

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up vote 8 down vote accepted

There are no currently known vulnerabilities in encryption in Ubuntu 11.10. There have been some. Generally the ecryptfs vulnerabilities involved an attacker already logged into your system who could cause denial of service. There was a LUKS problem in which users were surprised that a simple configuration option in a partitioning tool could fully and permanently destroy a partition.

In about 5 * 10^9 years, we expect this planet will be engulfed by the expanding Sun. AES-256 encryption can quite possibly resist attack for that long. However, as you seem to be aware, there are many other potential weaknesses and they bear repeating.

Will you know that you encrypted the disk effectively? It's complicated. Thoughtful people disagree about which installation options are sufficiently effective. Did you know that you're supposed to install full-disk encryption from Ubuntu's alternate install CD using LUKS, not ecryptfs? Did you know that LUKS has stored the passphrase in RAM in plain text, or that once a file is unlocked by any user via ecryptfs, then ecryptfs does not protect it from any other user? Was your disk ever connected to a system that permitted attaching unencrypted storage, rather than setting an explicit SELinux policy to prohibit that? Where did you keep your backups of your encrypted disk? You made backups because you knew that encrypted disks are much more sensitive to normal errors, right?

Are you sure your passphrase is not among the top billions (more like trillions, or whatever it is now) of possibilities that might be guessed? Is the person attempting to decrypt your disk really a random, poorly motivated and funded, unresourceful stranger? Are you sure your passphrase could not have been obtained by software tampering ("evil maid" attack), observing the running system ("shoulder surfing", "black bag" or "cold boot" attacks), etc.? How well have you avoided attacks that everyone gets: email and download viruses, malicious JavaScript, phishing?

How deeply are you committed to keeping your passphrase secret? What jurisdictions will you be in? Would you be content to go to prison? Are there other people who know the secrets that are protected by your disk encryption? Do you want to pay the price for your secrets even if those people reveal them?

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Interesting. I should note that I only encrypt disks used for backups. Not the primary bootable disks used in my machines. –  Cerin Feb 8 '12 at 14:45
    
IS there any evidence that the sun will expand to engulf the Earth in 5 billion years? Also, wouldn't your hard disk be on a healthier planet by then? –  hexafraction Jul 4 '12 at 0:48
    
Although there is some evidence of the Sun's eventual fate from the Hertzsprung-Russell diagram (which you could look up), you have correctly detected that I mentioned it just for fun. The point is that standard encryption techniques may be the least of your vulnerabilities. If you're serious about secrecy, you'll need to consider what you're protecting against (your threat model) and weigh your countermeasures accordingly. –  minopret Jul 6 '12 at 1:29

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