Securely erasing a flash drive in Windows with cipher

From time to time, we are given student flash drives either to use or to dispose of. For drives we intend to use, we usually consider using diskpart to clean them good enough. For drives we dispose of, we want to make sure that all data is securely erased so that no potentially-confidential or FERPA-relevant student data is leaked in the event that an enterprising person at an electronics recycler decides to have a peek.

Tools like DBAN can be used from a bootable environment to accomplish this task. However, this only allows you to wipe one flash drive at a time, and you cannot use the computer for anything else while it is running. What if you want to wipe several drives at once, or to wipe just one while doing other work on the computer?

The cipher command-line tool, also useful for encrypting or decrypting drives, can be used to securely erase the free space on a given volume by writing various bytes over any data that may be present so that it is unrecoverable. To use cipher to wipe a flash drive, follow these steps:

1. Reformat the disk using diskpart or some other tool.
2. Open a Command Prompt with administrator rights.
3. Run cipher /w:<drive letter>:\

Formatting the drive will ensure that the cipher tool considers it all to be "free space", and so overwrites the data. cipher will run for a fairly long time, depending on the size of the drive being erased. Once it has finished, the drive will be as clean as if it were brand-new.

It is worth noting that, because of the way flash memory works, you probably don't want to do this all the time to a flash drive, as each write slightly shortens the life of the memory. This may also cause marginal drives to finally fail, so keep that in mind if you intend to reuse a drive you are wiping.