[ale] erasing ext3 filesystems securely

Tue Jun 7 10:15:52 EDT 2005

On Tuesday 07 June 2005 05:05, James Sumners wrote:
> Kill it with a simple boot diskette -- http://dban.sourceforge.net/
I have something kinda like that...
A while back I ran across this little script. It's supposed to erase the drive 
completely, and afterwards it writes encrypted randomized data to the drive. 
Anyone thinking your drive might have something worth on it, will use a lot of 
time decrypting the contents only to find out they've been fooled...

I can't say how long it takes, 'cause I haven't used it yet. 

Best regards,
Ren?
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#!/usr/bin/perl

##### Things to do
# 1. Make sure we create a brand new directory for temporary mounting
#     in order to avoid security risks in case someone is logged in.
# 2. Use perl functions to handle a lot of the system calls. 
# 3. Let it autodetect hard drives, and floppy drives, and only perform
#    actions on unmounted hard drives and floppy drives.
##### 

use strict;
use Expect;
use Crypt::Blowfish;

#-----------------------------------------------
my $Junk;
  ### Set the drive to the slave drive on the Primary IDE controller.
my $Drive = "hdb";

  ### Let us do a lot of random stuff, and get the last line from the
  ### /etc/passwd file to make it really random, assuming one person
  ### has been added to the computer. 
my $time = time();
my $Ran = rand($time);
my $Ran = rand(10000000000000);
my $LastLine = `tail -n 1 /etc/passwd`; chomp $LastLine;
$LastLine = substr ($LastLine,0,30);
my $Blowfish_Key = $LastLine . $Ran . $time;
$Blowfish_Key = substr ($Blowfish_Key,0,20);
while (length ($Blowfish_Key) < 56) 
  {
  $Blowfish_Key .= $Ran = rand($time);
  }
$Blowfish_Key = substr ($Blowfish_Key,0,56);

  ### Done making up random key, now create Blowfish Encryption object.
my $Blowfish_Cipher = new Crypt::Blowfish $Blowfish_Key;

#------------------------------------
system "clear";
print "This will wipe out the hard drive on Drive /dev/$Drive\n";
print "Press enter to continue\n";
my $R = <STDIN>;

  ### Get the list of mounted partitions on the drive we want to wipe out
my @Mounted = `df`;
@Mounted = grep($_ =~ /\/dev\/hdb/, @Mounted);
  ### Foreach mounted partition, umount it
foreach my $Mount (@Mounted)
  {
  my ($Partition,$Junk) = split(/\s+/, $Mount,2);
  print "Unmounting $Partition\n";
  my $Result = system ("umount $Partition");
  if ($Result > 0) 
    {
    print "ERROR, unable to umount $Partition, aborting Script, Error = $Result\n";
    exit;
    }
  }

  ### Start the expect script, which will simulate someone doing this
  ### commands manually.
my $Fdisk = Expect->spawn("/sbin/fdisk /dev/$Drive");

  ### Get a list of mounted partitions by printing the partition table 
print $Fdisk "p\n";
my $match=$Fdisk->expect(30,"Device Boot    Start");

my $Temp = $Fdisk->exp_after();
my @Temp = split(/\n/, $Temp);
  ## Get the lines that tell us about the partitions
my @Partitions = grep($_ =~ /^\/dev\//, @Temp);

  ## Foreach line, delete the partition
foreach my $Line (reverse @Partitions)
  {
    ## Get the /dev/hdb part, and its number
  my ($Part,$Junk) = split(/[\t ]/, $Line,2);
  my $No = $Part;
  $No =~ s/^\/dev\/$Drive//;

  print "Deleting no $Drive $No\n";     

    ## Delete command
  print $Fdisk "d\n";    
  $match=$Fdisk->expect(30,"Partition number");

    ## Which partition number to delete
  print $Fdisk "$No\n";
  $match=$Fdisk->expect(30,"Command (m for help):");
  }

$Fdisk->clear_accum();

  ### If we had partitions, write changes, or otherwise, just end it
if (@Partitions < 1) {print $Fdisk "q\n"; $Fdisk->expect(2,":");}
else 
  {
  print $Fdisk "w\n";
  $Fdisk->expect(30,"Command (m for help):");
  }

#-------------------------------
  ## Get the geometry of the hard drive
my $Geometry = `/sbin/sfdisk -g /dev/$Drive`;
my ($Junk, $Cyl, $Junk2, $Head, $Junk3, $Sector, at Junk) = split(/\s+/,$Geometry);
if ($Cyl < 1) 
   {print "ERROR: Unable to figure out cylinders for drive. aborting\n"; exit;}

  ### Create a new expect script to simulate a person using fdisk
my $Fdisk = Expect->spawn("/sbin/fdisk /dev/$Drive");

   #### Tell fdisk to create new partition
print $Fdisk "n\n";
$Fdisk->expect(5,"primary");

  ### Tell it the new partition should be a primary partition
print $Fdisk "p\n";
$Fdisk->expect(5,":");

  ### Which partition, number 1
print $Fdisk "1\n";
$Fdisk->expect(5,":");

  ### Start at cylinder 1
print $Fdisk "1\n";
$Fdisk->expect(5,":");

  ### Go to the end
print $Fdisk "$Cyl\n";
$Fdisk->expect(5,":");

  ### Write and save
print $Fdisk "w\n"; 
$Fdisk->expect(30,"Command (m for help):");

#------------------------------------------
### Format the partition and mount it

my $Partition = "/dev/$Drive" . "1";
my $Result = system ("mkfs -t ext2 $Partition");
if ($Result > 0) {print "Error making partition, aborting.\n"; exit;}

   ### There should be better error checking here
system "umount /tmp/WIPE_IT";
system "rm -rf /tmp/WIPE_IT";
system "mkdir -p /tmp/WIPE_IT";
system "chmod 700 /tmp/WIPE_IT";

  ## See if we can mount the new partition.
my $Result = system ("mount $Partition /tmp/WIPE_IT");
if ($Result > 0) {print "Error mounting drive, aborting.\n"; exit;}
system "chmod 700 /tmp/WIPE_IT";

#--------------------------------
### Now create the file and stop when we hit the size.

my $Count = 0;
my $Written_Size = 0;  

  ### Open up a new file.
open(FILE,">>/tmp/WIPE_IT/Message.txt");
   ### If someone actually wants to screw around with your hard drive, 
   ### let us play with them and waste their time by adding a teaser. 
my $Ran = rand 259200000;   # between now and ten years ago (approx)
($Ran, $Junk) = split(/\./, $Ran, 2);
   ## New date minus random number of seconds
my $Date = `date --date '-$Ran seconds'`;

print FILE "DATE CREATED $Date\n";
my $Ran = rand 50;
($Ran, $Junk) = split(/\./, $Ran, 2);
$Ran = $Ran + 10;
print FILE "This document is extremely secure. It is a violation to let 
any unauthorized persons read it. Known password holders need to 
apply Method $Ran in order to decrypt binary data.\n"; 

  ### Create random number plus 25000
my $Ran = rand 25000;
($Ran, $Junk) = split(/\./, $Ran, 2);
$Ran = $Ran + 25000;

  ### Create an array of numbers which we will use most of the time.
my @Blank =  (1..$Ran);
  ### Take the array and make into a string.
my $Blank = "@Blank";
  ### Empty the array to free up memory.
@Blank = ();
my $B_Length = length $Blank;

  ### Let us get the amount of real space we have for the partition
my @Temp = `df`;
@Temp = grep($_ =~ /^$Partition/, @Temp);
my $Line = $Temp[0];
my ($Junk,$Blocks, at Junk) = split(/\s+/, $Line,4);
  ### We are assuming 1k blocks. 
my $Size = $Blocks*1000;

  ## While the file we have written is less than the size of the
  ## partition, print some more data. 
while ($Written_Size < $Size)
  {
  $Count++;

        ### 9 out of ten times, we just want to print blank spaces to hurry
        ### up printing. One out of ten times, print garbage binary.
     my $Ran = rand (10);
     if ($Ran > 1) 
       {
       print FILE $Blank; 
       $Written_Size = $Written_Size + $B_Length; 
       }  
     else 
       {
         ## This part makes a long string (upto 10000 bytes) of random data. 
       my $Garbage = "";
       my $Length = rand(10000);
       ($Length, $Junk) = split(/\./, $Length, 2);
       for (my $i = 0; $i < $Length; $i++)
         {
         my $Ran = rand 256;
         ($Ran, $Junk) = split(/\./, $Ran, 2);
         $Garbage .= chr $Ran;
         }
         ## This parts encrypts the random data 8 bytes at a time. 
       my $Temp = $Garbage;
       my $Encrypted = "";
       while (length $Temp > 0)  
         {
         while (length $Temp < 8) {$Temp .= "\t";}
         my $Temp2 = $Blowfish_Cipher->encrypt(substr($Temp,0,8));
         $Encrypted .= $Temp2; 
         if (length $Temp > 8) {$Temp = substr($Temp,8);} else {$Temp = "";}
         }

         ### Print the encrypted random data to file. 
       print FILE $Encrypted;
       $Length = length $Encrypted;

       $Written_Size = $Written_Size + $Length;
       my $Rest = $Size - $Written_Size;Securely 
       print "$Size - $Written_Size = $Rest to go\n";
       }

   ### At every 500 prints, start saving to a new file.  
  if ($Count =~ /500$/) 
    {
    close FILE;
    open(FILE,">>/tmp/WIPE_IT/$Count");
    }
  }

close FILE;
#----------------------------------------------------

my $Result = system ("umount $Partition");
if ($Result > 0) {print "Error unmounting partition $Partition, aborting.\n"; exit; }

  ### Let us reformat the partition. Doesn't delete data, just removes it
  ### from the directory. 
my $Result = system ("mkfs -t ext2 $Partition");
if ($Result > 0) {print "Error making partition, aborting.\n"; exit;}