I opened the flash drive with my Hex Editor and took a note of where the file was on the flash drive. I then saved the text file to the flash drive. I made a large text file with some readable English text in it. Using a Corsair 256MB Flash Drive I first zeroed the entire drive. I have read this thread with some interest and I thought I would do my own experiment.
USB SECURE KEY FULL
If that's the case then a full erase might effectively erase the USB key drive because each cell will be occupied with random data. My understanding of how eraser does the full drive erase is it completely fills the drive with files that contain random data and after the drive is completely full, it deletes those files. I'm beginning to change my mind about the full-drive erase though.
USB SECURE KEY FREE
Your old data is still there, just marked "available" so the OS recognizes it as free space. Therefore, Eraser doesn't actually write over the old file with its new file because the USB key drive redirects the writes to random cells, not the cells that your data originally occupied. Instead, it marks those cells as available (but the contents still remain) and then writes the new copy to other cells and updates the FAT to indicate where the new data is being written. When you save a new copy of a file over an old copy of the file in a USB drive, it doesn't overwrite the cells that the old copy occupies. The problem lay in the fact that it is not "overwriting" the file. Some good discussion of this issue can be found at: Įncryption of your USB key also offers another benefit over "erasing." Encrypting your USB key instead of "erasing" also reduces the wear on the key's memory cells from repeat file writes during "erasure" of the USB key. Instead put your data in an encrypted volume on the key or encrypt the entire USB key. Therefore, in short, don't rely on "erasing" a USB key for security. In that case, all the memory is at least encrypted. The old data will be marked as "old", and will not be erased until the block has to be reusedĮven doing a complete wipe of a key doesn't guarantee that you'll overwrite every cell in the usb key! Therefore, if security is really at issue and you want to secure your USB key, I advise that you use an encryption program, such as Truecrypt. Instead it writes it to unused blocks and directs subsequent read accesses to these blocks. Their site states: When a file needs to be updated, TrueFFS (through NFTL) does not overwrite the old data. Take for example, a popular version of wear-leveling in USB keys found in TrueFFS.
Therefore, since Eraser essentially writes files full of random data a certain number of times, there is no way of knowing if the particular data you wanted "erased" has in fact been overwritten even once. This extends the operative life of the key because any one memory cell has a limited number of writes before it dies. Whenever a file is written to the USB key, it distrubtes the file in a psuedo-random fashion across the key's memory cells so that no one cell gets written too many times. USB drives use wear-levelling algorithms - sort of a low level file format that resides in the key and is lower level than the operating system's file system. Virtually every post I've seen on the subject here states that USB drives can be securely erased using eraser "because they are magnetic." However, that's simply not the case. There seems to be a serious misunderstanding about the way USB drives work on this forum which can lead to security risks.
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