

The Eraser  -  Military Secure File Deletion                     README.txt
--------------------------------------------                     ----------


TheEraser  is  a Military-Grade privacy file cleaner and secure file wiping
utility  using  advanced  cryptographic  algorithms to ensure nobody and no
recovery  tool  will be able to undelete any file which will may break your
privacy and/or expose sensitive material.

It  begun  with the basics of the well know DoD 5250 methods, which we took
as base of our work, but achieved to make it somewhat better mixing diverse
techniques  altogether  -  not  only  overwriting  the  file in one step is
sufficient,  we  seek  the  file  several times at random offsets and using
random  blocks  attacking  the  filesystem  where it less thinks, we should
state  that  most  of  the  techniques  implemented on this application was
inspired  by the paper published in the USENIX Security Symposium where the
analyst Peter Gurman wrote:

With  the use of increasingly sophisticated encryption systems, an attacker
wishing  to  gain  access to sensitive data is forced to look elsewhere for
information.   One  avenue  of  attack is the recovery of supposedly erased
data  from magnetic media or random-access memory.  This covers some of the
methods  available to recover erased data and presents schemes to make this
recovery significantly more difficult.

The  general  concept behind an overwriting scheme is to flip each magnetic
domain  on  the  disk back and forth as much as possible (this is the basic
idea  behind  degaussing)  without writing the same pattern twice in a row.
If  the  data  was  encoded  directly,  we  could simply choose the desired
overwrite  pattern  of  ones  and zeroes and write it repeatedly.  However,
disks generally use some form of run-length limited (RLL) encoding, so that
the  adjacent  ones won't be written.  This encoding is used to ensure that
transitions  aren't  placed  too  closely together, or too far apart, which
would mean the drive would lose track of where it was in the data.

To  erase  magnetic  media,  we  need  to  overwrite  it  many  times  with
alternating  patterns in order to expose it to a magnetic field oscillating
fast  enough that it does the desired flipping of the magnetic domains in a
reasonable  amount of time.  Unfortunately, there is a complication in that
we  need  to  saturate the disk surface to the greatest depth possible, and
very  high  frequency  signals  only  "scratch the surface" of the magnetic
medium  (this  phenomenon  was  used  to  good  effect  when HiFi VCRs were
introduced  by  writing  the  stereo  FM  audio signal at a lower frequency
beneath  the  higher-frequency  video  signal,  a  technique known as depth
multiplex  recording).   Disk  drive  manufacturers,  in  trying to achieve
ever-higher  densities,  use  the  highest possible frequencies, whereas we
really require the lowest frequency a disk drive can produce.  Even this is
still  rather  high.   The  best  we  can do is to use the lowest frequency
possible  for  overwrites,  to  penetrate  as  deeply  as possible into the
recording medium.

Using  our  knowledge  of  how the data is encoded, we can now choose which
decoded  data  patterns  to  write  in  order to obtain the desired encoded
signal.   The  encoding  methods described above cover the vast majority of
magnetic  disk  drives.   However,  each  of  these  has  several  possible
variants.   With  MFM,  only one is used with any frequency, but the newest
(1,7)  RLL code has at least half a dozen variants in use.  For MFM with at
most  four  bit  times  between  transitions,  the  lowest  write frequency
possible  is  attained  by writing the repeating decoded data patterns 1010
and  0101.   These have a 1 bit every other "data" bit, and the intervening
"clock" bits are all 0.  We would also like patterns with every other clock
bit set to 1 and all others set to 0, but these are not possible in the MFM
encoding  (such "violations" are used to generate special marks on the disk
to identify sector boundaries).  The best we can do here is three bit times
between  transitions,  which is generated by repeating the decoded patterns
100100,  010010  and  001001.   We  should  use  several  passes with these
patterns,  as MFM drives are the oldest, lowest-density drives around (this
is especially true for the very-low-density floppy drives).

Data  overwritten  once  or  twice  may be recovered by subtracting what is
expected to be read from a storage location from what is actually read, and
data which is overwritten an arbitrarily large number of times can still be
recovered  provided that the new data isn't written to the same location as
the  original data, or that the recovery attempt is carried out fairly soon
after the new data was written, TheEraser takes this into account carefully
forcing  the  Operating  System and FileSystem (where the file to be erased
resides)  to  e.g.   disable  Disk Caches and buffered writes, ensuring the
data is properly/secure destroyed.

TheEraser  implements  two  erasing  methods,  when you're about to erase a
file,  or  folder, you'll be prompted about which one to use, here you have
to  choose  between  the  "Safe Mode" or "Quick Mode", our quick mode works
closer  to the DoD method and it's recommended for normal non very-relevant
files,  while the safe mode uses high techniques of erasure which makes the
process very slow but ensures the data is destroyed forever.

You  can  erase  single  files or complete folders with all of his contents
(including  subdirectories  recursively!),  hence  take care when selecting
folders!  and be sure you will no longer need any of the files found in the
root or any of his subdirectories!

Last  but  no least, note the application is designed on a portable fashion
(does not require installation), everything needed is builded into a single
executable  file,  so  that  you  can  copy  it into you usb stick and e.g:
remove files securely when you're working on a computer which isn't yours.


Don't hesitate to contact us if you have some question.

Our website is [temporarly] available from: http://casoft.pcriot.com

Contact us at: <casoft-dev{-at-}hotmail.com>


Copyright  2008 CASOFT - Software Solutions
--------------------------------------------

                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
