Device versus file based encryption in TrueCrypt for a flash drive?

Question

Are there security tradeoffs to be considered in deciding between encrypting an entire flashdrive with TrueCrypt versus storing a file encrypted container? The security goal is to be immune to the problem that wear leveling can store data on unused areas of the flash drive, so that all the encrypted data remains secure if the flash drive is lost.

If the entire device is encrypted, then the flash drive is useless without installing TrueCrypt. If a file container is used, then an unencrypted portion could still be used for other purposes (understanding that wear leveling could leave traces of those files), but does that create any vulnerability for the file encrypted portion?

Note that I understand that neither approach solves the problem of file fragments being left elsewhere in the system, e.g. in a swap file, without encrypting the entire system - that's not my question.

Answer 1

Truecrypt has an article discussing wear-leveling. It would appear that Truecrypt still provides a secure solution as long as you can be sure that your keys have not been compromised. It makes no statement regarding the differences between file-based containers vs. device-based encryption, and so it is likely there are no security tradeoffs to be had aside from those you've already stated.

Therefore, multiple "versions" of a single sector may be available to an attacker. This may have various security implications. For instance, when you change a volume password/keyfile(s), the volume header is, under normal conditions, overwritten with a re-encrypted version of the header. However, when the volume resides on a device that utilizes a wear-leveling mechanism, TrueCrypt cannot ensure that the older header is really overwritten. If an adversary found the old volume header (which was to be overwritten) on the device, he could use it to mount the volume using an old compromised password (and/or using compromised keyfiles that were necessary to mount the volume before the volume header was re-encrypted). Due to security reasons, we recommend that TrueCrypt volumes are not created/stored on devices (or in file systems) that utilize a wear-leveling mechanism (and that TrueCrypt is not used to encrypt any portions of such devices or filesystems).