Is software shredding reliable?

[loveranger]

I work with many private and confidential information through a portable hard drive. Only until recently have I used encryption to protect the files I work with (Truecrypt). I've deleted all the files on the hard drive and used Eraser to shred the free space using DOD. Is it possible, even by the data forensic experts, to retrieve the files I've deleted? I know physical destruction is 100% peace of mind but it's a waste of money. What is the science behind DOD algorithm and the hard/portable/flash drives. Is it possible data could still be recovered once it's overwritten?

PS. I noticed once you delete files inside a Truecrypt container, it goes to the recycle bin. I empty it as usual... are the files still encrypted?

 

[Joel]

I work with many private and confidential information through a portable hard drive. Only until recently have I used encryption to protect the files I work with (Truecrypt). I've deleted all the files on the hard drive and used Eraser to shred the free space using DOD. Is it possible, even by the data forensic experts, to retrieve the files I've deleted?

From a security standpoint, yes, it would be possible. The probability is minute, but non-zero. From an engineering standpoint, no, the amount of resources needed to extract usable information from such a disk would be rather expansive. Ultimately it is your threat model and your anticipated adversaries. This is paranoia vs. pragmatism.

I know physical destruction is 100% peace of mind but it's a waste of money. What is the science behind DOD algorithm and the hard/portable/flash drives. Is it possible data could still be recovered once it's overwritten?

Basically the reasons for each drive erasure method is just a set of guidelines developed by the originator of the design. Usually, the originator will have the design document which should detail the rationale for its design. I won't detail on every single erasure method here since there are a lot, you may want to read up on it.

PS. I noticed once you delete files inside a Truecrypt container, it goes to the recycle bin. I empty it as usual... are the files still encrypted?

Yes, the recycle bin stores files on the same drive as it was deleted from. But remember if the key for the container is compromised the problem of data remanence.