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What are possible drawbacks of using TrueCrypt? Do I risk losing my data in case of some disk error?

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up vote 7 down vote accepted

Negative aspect:

  • Harder to recover data if the disk breaks
  • Added complexity
  • Performance hit (rather small, though)

Positive things: better data confidentiality - without your passphrase, it is virtually impossible to access your data. Assuming your passphrase is secure enough, and you're not forced to give it to someone. And assuming disk is offline - obviously malware/spyware can still access the data, when encrypted disk is in use.

There's two distinct cases: full disk encryption and disk images. In both formats, there's TrueCrypt header at the beginning of encrypted partition. This disk header is essential for accessing the contents, as your passphrase is only used to decrypt encryption key stored on the header. That encryption key is then used for disk encryption/decrypting.

With full system encryption, Truecrypt requires burning restore CD. That can be used to restore corrupted disk header, due to disk failure or data corruption. With that it is possible to decrypt disk, even if disk header is corrupted. Restoring disk contents using some commercial service might be even more expensive/impossible.

With disk images, there's no mandatory backup of disk header. Therefore, even a single-bit corruption in the beginning of disk destroys all contents (does not destroy, but you have no way to access that anymore).

Quote from Truecrypt FAQ:

What will happen when a part of a TrueCrypt volume becomes corrupted?

In encrypted data, one corrupted bit usually corrupts the whole ciphertext block in which it occurred. The ciphertext block size used by TrueCrypt is 16 bytes (i.e., 128 bits). The mode of operation used by TrueCrypt ensures that if data corruption occurs within a block, the remaining blocks are not affected.

If the header is not corrupted, a single-bit corruption only corrupts 16 bytes (i.e 0.00000149% of one gigabyte). Single-bit errors happen randomly. That is called bit rot.

As with any computer system, with encrypted device, it is a good idea to take backups. If possible, do not back up encrypted disk (images), as any problem with TrueCrypt will ruin the backups. It is really advisable to encrypt backups with different system, for example, with PGP.

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So in the case when a block of data (not including header) is damaged, I lose only data stored in this block? – user66548 Feb 8 '11 at 12:22
Yes, that is correct. I also modified my answer accordingly. – Olli Feb 8 '11 at 13:21
No you don't lose your data because you have made regular backups that you keep in a secure place ;-) – Linker3000 Feb 8 '11 at 13:39
@user66548: if this provided answer to your question, you should accept it (…) – Olli Feb 15 '11 at 13:27
@Linker3000, bad answer. My backup is encrypted too. It would be stupid to leave it open :) – user66548 Apr 15 '11 at 7:20

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