• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 975
  • Last Modified:

Shred (Secure Delete) a file in NTFS

I need a secure way to delete a file.
I've gone through the standard procedure of overwriting 6 times with 0 and 255 bytes and then with random data, but when I scan the disk, I see a copy of the information is there.
I've used:

  public static void secureDelete(File file, byte[] b) throws IOException {
    if (file.exists()) {
      long length = file.length();
      SecureRandom random = new SecureRandom();
      RandomAccessFile raf = new RandomAccessFile(file, "rws");
      raf.seek(0);
      raf.getFilePointer();
      byte[] data = new byte[50];
      int pos = 0;
      while (pos < length) {
        random.nextBytes(data);
        raf.write(data);
        pos += data.length;
      }
      raf.close();
      file.delete();
    }
  }

using as 'b' zeros, 255 and random numbers.
It works for FAT but not for NTFS
0
RNMisrahi
Asked:
RNMisrahi
  • 4
  • 3
  • 2
2 Solutions
 
objectsCommented:
0
 
lenordisteCommented:
Your code is rewriting random data inside a file making the assumption that the OS will actually write the data in place where the file is located. It probably works for some "old" file systems like FAT32 but it sure won't work for NTFS. I don't think this can be achieved without wiping the whole drive.
0
 
RNMisrahiAuthor Commented:
If it is true that on an NTFS Secure Delete is impossible (and you guys may be right), how come there are some applications that do that? I mean, they don't wipe all the empty space. So how do they do that? Or is it that there is no guarantee that they do work?
0
Improve Your Query Performance Tuning

In this FREE six-day email course, you'll learn from Janis Griffin, Database Performance Evangelist. She'll teach 12 steps that you can use to optimize your queries as much as possible and see measurable results in your work. Get started today!

 
objectsCommented:
> I mean, they don't wipe all the empty space.

do you know that for a fact?
Native applications can operate at a much lower level than Java can
0
 
RNMisrahiAuthor Commented:
I'm ready to accept the fact that it is impossible to guarantee secure deleting on an NTFS, but I cannot imagine these utilities wiping all the empty space on a 1 TB disk in a few seconds. I have a 360GB disk, over half of it is free and when they delete (as far as I can see so far), the info is not there anymore. When I use an app such as HxD to scan the surface for a specific string, it is not there anymore. The HxD app takes hours to scan the whole disk.

But if Java cannot do this, can this be done with C# or Delphi?

0
 
lenordisteCommented:
there's either no guarantee that they do work or they are written using a low level language
0
 
RNMisrahiAuthor Commented:
Good to know what can and cannot be done.
0
 
lenordisteCommented:
look at the comment from theUnhandledException (one of the last comments) since it's spot on about your problem:
http://stackoverflow.com/questions/4147775/securely-deleting-a-file-in-c-net

as he advises, the solution may be to reconsider the problem and encrypt the files you are writing to disk with a dynamic encryption key.
0
 
lenordisteCommented:
I've never workd with Delphi, but I know for sure this cannot be achieved in Java or C#.
0
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Featured Post

Improved Protection from Phishing Attacks

WatchGuard DNSWatch reduces malware infections by detecting and blocking malicious DNS requests, improving your ability to protect employees from phishing attacks. Learn more about our newest service included in Total Security Suite today!

  • 4
  • 3
  • 2
Tackle projects and never again get stuck behind a technical roadblock.
Join Now