On Sat, Apr 18, 2015 at 7:01 AM, Bradley Remedios <bremedios@gmail.com> wrote:

I have a question about what YAFFS2 supports for providing a mechanism
to securely delete a file so that it cannot be recovered once deleted.

We are looking for a file system that supports the concept of secure
delete, either by performing a block erase that encompasses all
outstanding pages, or by utilizing Cryptographic Encryption on a
per-file basis.

Our main requirement is to support the ability to perform a secure
delete. We do not require the data on the drive to be unreadable
until we go to delete the file. If we are using Cryptographic
Encryption we would need the encryption key that is used to be unique
per file as we would only want to have to delete a single file to
cause the contents to become unreadable.

I took a look at the yaffs.net site and didn't see anything that
seemed to specifically outline that it supports Cryptographic
Encryption itself or what level of encryption that it is using. I
have seen a few research papers on people that have made the
modifications themselves.

Am I missing something, or is it accurate that YAFFS2 does not support
any secure delete functionality or a Cryptographic Encryption feature
that could be used for the same purpose.

Yaffs does not have any encryption or secure deletion feature per se, but it is still possible to achieve this quite easily in two ways:

1) Loop mounting: If you're using Linux then you can loop mount onto Yaffs thus making Yaffs the underlying media for some other fs that has the features you want.

2) Using background garbage collection (on by default in Linux):

Yaffs is log structured which means all file activity happens by writing to the end of the log and space is reclaimed by identifying blocks with unused data (eg. parts of deleted files), rewriting the useful data and then erasing the block.

By tweaking the garbage collection thresholds you can get Yaffs to clean up quite promptly meaning that soon after a file is deleted, the garbage collector will erase all that file's data from the file system.

-- CHarles