Deleted file recovery program using C C++

问题:

I want to write a program that can recover deleted files from hard drive ( FAT32/NTFS partition Windows). I don't know where to start from. What should be the starting point of this? What should i read to pursue this? Help is required. Which system level structs should i study?

回答1:

It's entirely a matter of the filesystem layout, how a "file" actually looks on disk, and what remains when a file is deleted. As such, pretty much all you need to understand is the filesystem spec (for each and every filesystem you want to support), and how to get direct block-level access to the HD data. It might be possible to reuse some code from existing filesystem drivers, but it will need to be modified to process structures that, from the point of view of the filesystem, are gone.

• NTFS technical reference
• NTFS.com
• FAT32 spec

回答2:

You should know first how file deletion is done in FAT32/NTFS, and how other undelete softwares work.

Undelete software understands the internals of the system used to store files on a disk (the file system) and uses this knowledge to locate the disk space that was occupied by a deleted file. Because another file may have used some or all of this disk space there is no guarantee that a deleted file can be recovered or if it is, that it won't have suffered some corruption. But because the space isn't re-used straight away there is a very good chance that you will recover the deleted file 100% intact. People who use deleted file recovery software are often amazed to find that it finds files that were deleted months or even years ago. The best undelete programs give you an indication of the chances of recovering a file intact and even provide file viewers so you can check the contents before recovery.

Here's a good read (but not so technical): http://www.tech-pro.net/how-to-recover-deleted-files.html

回答3:

This is not as difficult as you think. You need to understand how files are stored in fat32 and NTFS. I recommend you use winhex an application used for digital forensics to check your address calculations are correct.

Ie NTFS uses master file records to store data of the file in clusters. Unlink deletes file in c but if you look at the source code all it does is removes entry from table and updates the records. Use an app like winhex to read information of the master file record. Here are some useful info.

Master boot record - sector 0 Hex 0x55AA is the end of MBR. Next will be mft File name is mft header. There is a flag to denote folder or file (not sure where). The file located flag tells if file is marked deleted. You will need to change this flag if you to recover deleted file. You need cluster size and number of clusters as well as the cluster number of where your data starts to calculate the start address if you want to access data from the master file table.

Not sure of FAT32 but just use same approach. There is a useful 21 YouTube video which explains how to use winhex to access deleted file data on NTFS. Not sure the video but just type in winhex digital forensics recover deleted file. Once you watch this video it will become much clearer. good luck

Just watched the 21 min YouTube video on how to recover files deleted in NTFS using winhex. Don't forget resident flag which denotes if the file is resident or not. This gives you some idea of how the file is stored either in clusters or just in the mft data section if small. This may be required if you want to access the deleted data. This video is perfect to start with as it contains all the offset byte position to access most of the required information relative to beginning of the file record. It even shows you how to do the address calculation for the start of the cluster. You will need to access the table in binary format using a pointer and adding offsets to the pointer to access the required information. The only way to do it is go through the whole table and do a binary comparison of the filename byte for byte. Some fields are little eindian so make sure you got winhex to check your address calculations.

回答4:

There are thousands of such programs, why waste time on another? Maybe it would be better to learn, fork or contribute to existing opensourced one.