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I wonder if TrueCrypt rescue disk even makes sense to keep. Lets assume for a second there is a corruption on the disk. Rescue disk will not help here, because the data is invalid anyway. But on the same note, if you are using TC to prevent sensitive data from possibly being decrypted by bad guys, then recovery disk just gives them such opportunity. Am I wrong?

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All the rescue disk can do is restore the key data. You still need the password to decrypt the disk. So no, not a security risk, and a good idea to have (I keep an ISO instead so I don't have to worry about a CD getting scratched).

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you know for sure it has no key on it? My impression was that it could be used to recover password –  galets Apr 18 '12 at 21:42
    
Verified, password still required when using TC recovery disk. Thanks! –  galets Apr 18 '12 at 21:52
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Nope, disk has only a key encrypted. Writing password on the disk is BAAAAAD We print super long initial password on TC rescue disk using lightscribe, and hide them from user.... a bit of effort on first login, even worse having disk in drive and reading pass off it... (we own the computer, so we do as we like)

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First and foremost, the documentation for the TrueCrypt Rescue Disk makes it clear that the key material on the rescue disk remains password-encrypted. However, the rescue disk is a security risk in the same sense that anyone with access to key material can attempt to brute-force the key. This is really no different than someone gaining access to your SSH private key, or the private half of your GPG key-pair. Even if those keys are password-protected (as they should be), they are vulnerable to the same brute-force and password-guessing attacks as any other password system once they fall into the wrong hands.

Restoring the key data from a TrueCrypt rescue disk also restores the key's password to the point in time when the rescue disk was created. So, if you've changed your password since the rescue disk was created, perhaps for security reasons like:

  1. The password was compromised (e.g. someone saw you type it in).
  2. The password was updated in accordance with a password-aging policy.
  3. The password was changed because it was too short, or too easy to guess.

the rescue disk will (by definition) restore the password for your TrueCrypt encryption key to a less secure state.

As with any security scenario, you have to examine your threat model. As long as you choose strong passphrases, replace rescue disks when you update your passphrase, destroy obsolete rescue disks, and keep the disks secure in the same way you keep any other sensitive data secure, you should be fine under normal levels of professional paranoia.

If a professional cryptographer or forensics expert is after you, though, you may have an entirely different set of problems, and your threat model should probably reflect that. It is the offline aspect of the rescue disk that slightly increases your security exposure, as the key material present on the rescue disk is pretty much the same as what's on your hard drive, so you will certainly want to limit unauthorized physical access to both for similar reasons.

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