Provided by: wipe_0.24-7_amd64 bug

NAME

       wipe - securely erase files from magnetic media

SYNOPSIS

       wipe [options] path1 path2 ... pathn

CURRENT-VERSION

       This manual page describes version 0.22 of wipe , released November 2010.

DESCRIPTION

       Recovery  of  supposedly  erased  data from magnetic media is easier than what many people
       would like to believe. A technique called  Magnetic  Force  Microscopy  (MFM)  allows  any
       moderately  funded  opponent  to  recover  the last two or three layers of data written to
       disk; wipe repeatedly overwrites special patterns to the files to be destroyed, using  the
       fsync()  call  and/or the O_SYNC bit to force disk access. In normal mode, 34 patterns are
       used (of which 8 are random). These patterns were recommended in  an  article  from  Peter
       Gutmann  (pgut001@cs.auckland.ac.nz)  entitled  "Secure Deletion of Data from Magnetic and
       Solid-State Memory". The normal mode takes 35 passes (0-34). A quick mode  allows  you  to
       use only 4 passes with random patterns, which is of course much less secure.

NOTE ABOUT JOURNALING FILESYSTEMS AND SOME RECOMMENDATIONS (JUNE 2004)

       Journaling  filesystems  (such  as Ext3 or ReiserFS) are now being used by default by most
       Linux distributions.  No secure deletion program  that  does  filesystem-level  calls  can
       sanitize  files on such filesystems, because sensitive data and metadata can be written to
       the journal, which cannot  be  readily  accessed.   Per-file  secure  deletion  is  better
       implemented in the operating system.

       Encrypting a whole partition with cryptoloop, for example, does not help very much either,
       since there is a single key for all the partition.

       Therefore wipe is best used to sanitize a harddisk before giving it to  untrusted  parties
       (i.e. sending your laptop for repair, or selling your disk).  Wiping size issues have been
       hopefully fixed (I apologize for the long delay).

       Be aware that harddisks are quite intelligent beasts those days.  They transparently remap
       defective  blocks.  This means that the disk can keep an albeit corrupted (maybe slightly)
       but inaccessible and unerasable copy of some of your data.  Modern disks are said to  have
       about  100%  transparent remapping capacity.  You can have a look at recent discussions on
       Slashdot.

       I hereby speculate that harddisks can use the spare remapping area to secretly make copies
       of  your  data.   Rising  totalitarianism  makes  this  almost  a  certitude.  It is quite
       straightforward to implement some simple filtering schemes  that  would  copy  potentially
       interesting  data.   Better,  a  harddisk  can  probably detect that a given file is being
       wiped, and silently make a copy of it, while wiping the original as instructed.

       Recovering such data is probably easily done with secret IDE/SCSI commands.  My  guess  is
       that  there  are agreements between harddisk manufacturers and government agencies.  Well-
       funded mafia hackers should then be able to find those secret commands too.

       Don't trust your harddisk.  Encrypt all your data.

       Of course this shifts the trust to the computing system, the CPU,  and  so  on.   I  guess
       there  are  also  "traps"  in  the  CPU and, in fact, in every sufficiently advanced mass-
       marketed chip.  Wealthy nations can find those.   Therefore  these  are  mainly  used  for
       criminal investigation and "control of public dissent".

       People should better think of their computing devices as facilities lended by the DHS.

IMPORTANT WARNING -- READ CAREFULLY

       The  author,  the  maintainers  or  the  contributors  of  this  package  can  NOT be held
       responsible in any way if wipe destroys something you didn't want it  to  destroy.   Let's
       make this very clear. I want you to assume that this is a nasty program that will wipe out
       parts of your files that you didn't want it to wipe. So whatever happens after you  launch
       wipe  is  your  entire  responsibility.   In  particular, no one guarantees that wipe will
       conform to the specifications given in this manual page.

       Similarly, we cannot guarantee that wipe will actually erase data, or that wiped  data  is
       not  recoverable  by  advanced  means.   So if nasties get your secrets because you sold a
       wiped harddisk to someone you don't know, well, too bad for you.

       The best way to sanitize a storage medium is  to  subject  it  to  temperatures  exceeding
       1500K.   As  a cheap alternative, you might use wipe at your own risk. Be aware that it is
       very difficult to assess whether running wipe on a given file will actually wipe it --  it
       depends  on an awful lot of factors, such as : the type of file system the file resides on
       (in particular, whether the file system is a journaling one or not), the type  of  storage
       medium used, and the least significant bit of the phase of the moon.

       Wiping  over  NFS  or over a journalling filesystem (ReiserFS etc.) will most probably not
       work.

       Therefore I strongly recommend to call wipe directly on  the  corresponding  block  device
       with the appropriate options. However THIS IS AN EXTREMELY DANGEROUS THING TO DO.  Be sure
       to be sober. Give the right options. In particular : don't wipe a whole harddisk (eg. wipe
       -kD  /dev/hda  is  bad)  since this will destroy your master boot record. Bad idea. Prefer
       wiping partitions (eg. wipe -kD /dev/hda2) is good, provided, of  course,  that  you  have
       backed up all necessary data.

COMMAND-LINE OPTIONS

       -f (force; disable confirmation query)
            By  default  wipe  will  ask  for  confirmation, indicating the number of regular and
            special files and directories specified on the command line. You must type "yes"  for
            confirmation,  "no" for rejection. You can disable the confirmation query with the -f
            (force) option.

       -r (recurse into subdirectories)
            Will allow the removal of the entire directory tree. Symbolic links are not followed.

       -c (chmod if necessary)
            If a file or directory to be wiped has no write permissions set, will do a  chmod  to
            set the permission.

       -i (informational, verbose mode)
            This enables reporting to stdout. By default all data is written to stderr.

       -s (silent mode)
            All messages, except the confirmation prompt and error messages, are suppressed.

       -q (quick wipe)
            If  this  option  is  used,  wipe  will only make (by default) 4 passes on each file,
            writing random data. See option -Q

       -Q <number-of-passes>
            Sets the number of passes for quick wiping. Default is 4. This option requires -q.

       -a (abort on error)
            The program will exit with EXIT_FAILURE if a non-fatal error is encountered.

       -R (set random device OR random seed command)

            With this option which requires an argument you can specify an alternate  /dev/random
            device,  or  a  command  who's  standard  output will be hashed using MD5-hashed. The
            distinction can be made using the -S option.

       -S (random seed method)

            This option takes  a  single-character  argument,  which  specifies  how  the  random
            device/random  seed argument is to be used. The default random device is /dev/random.
            It can be set using the -R option.

       The possible single-character arguments are:
       r    If you want the argument to be treated like a  regular  file/character  device.  This
            will work with /dev/random, and might also work with FIFOs and the like.
       c    If  you  want  the  argument to be executed as a command. The output from the command
            will be hashed using  MD5  to  provide  the  required  seed.  See  the  WIPE_SEEDPIPE
            environment variable for more info.
       p    If  you  want wipe to get its seed by hashing environment variables, the current date
            and time, its process id. etc. (the random device argument will not be used). This is
            of course the least secure setting.

       -M (select pseudo-random number generator algorithm)

       During  the  random passes, wipe overwrites the target files with a stream of binary data,
       created by the following choice of algorithms:
       l    will use (depending on your system)  your  libc's  random()  or  rand()  pseudorandom
            generator.  Note  that  on  most  systems, rand() is a linear congruential generator,
            which is awfully weak. The choice is made at compile-time with the HAVE_RANDOM define
            (see the Makefile).
       a    will  use  the Arcfour stream cipher as a PRNG. Arcfour happens to be compatible with
            the well-known RC4 cipher. This means that under  the  same  key,  Arcfour  generates
            exactly the same stream as RC4...
       r    will  use  the fresh RC6 algorithm as a PRNG; RC6 is keyed with the 128-bit seed, and
            then a null block is repeatedly encrypted to get the pseudo-random stream.   I  guess
            this  should  be  quite secure. Of course RC6 with 20 rounds is slower than random();
            the compile-time option WEAK_RC6 allows you to use a 4-round version of RC6, which is
            faster.  In  order  to  be  able  to  use  RC6, wipe must be compiled with ENABLE_RC6
            defined; see the Makefile for warnings about patent issues.

            In all cases the PRNG is seeded with the data gathered from the random device (see -R
            and -S options).

       -l <length>
            As  there  can  be some problems in determining the actual size of a block device (as
            some devices do not even have fixed sizes, such as floppy disks or tapes), you  might
            need  to  specify  the  size  of  the device by hand; <length> is the device capacity
            expressed as a number of bytes. You can use K (Kilo)  to  specify  multiplication  by
            1024,   M   (Mega)  to  specify  multiplication  by  1048576,  G  (Giga)  to  specify
            multiplication by 1073741824 and b (block) to specify multiplication by 512. Thus

            1024 = 2b = 1K

                                20K33 = 20480+33 = 20513

                                114M32K = 114*1024*1024+32*1024.

       -o <offset>
            This allows you to specify an offset inside the file  or  device  to  be  wiped.  The
            syntax of <offset> is the same as for the -l option.

       -e   Use exact file size: do not round up file size to wipe possible remaining junk on the
            last block.

       -Z   Don't try to wipe file sizes by repeatedly halving the file size. Note that  this  is
            only  attempted  on  regular  files so there is no use if you use wipe for cleaning a
            block or special device.

       -X <number>
            Skip a given number of passes.  This is useful to continue wiping from a given  point
            when  you  have  been  wiping,  say, a large disk and had to interrupt the operation.
            Used with -x.

       -x <pass1>,...,<pass35>
            Specify the pass order.  When wipe is interrupted, it will print the current randomly
            selected  pass  order  permutation  and  the  pass  number  as  appropriate -x and -X
            arguments.

       -F   Don't try to wipe file names. Normally, wipe tries to cover file  names  by  renaming
            them;  this  does  NOT guarantee that the physical location holding the old file name
            gets overwritten.  Furthermore, after renaming a file, the only way to make sure that
            the  name  change is physically carried out is to call sync (), which flushes out ALL
            the disk caches of the system, whereas for ading and writing one can use  the  O_SYNC
            bit  to  get  synchronous  I/O for one file. As sync () is very slow, calling sync ()
            after every rename () makes filename wiping extremely slow.

       -k   Keep files: do not unlink the files after they have been overwritten. Useful  if  you
            want to wipe a device, while keeping the device special file. This implies -F.

       -D   Dereference  symlinks: by default, wipe will never follow symlinks. If you specify -D
            however, wipe will consent to, well, wipe the  targets  of  any  symlinks  you  might
            happen  to  name  on  the command line.  You can't specify both -D and -r (recursive)
            options, first because of possible cycles in the  symlink-enhanced  directory  graph,
            I'd  have  to  keep  track  of  visited files to guarantee termination, which, you'll
            easily admit, is a pain in C, and, second, for fear of having  a  (surprise!!)  block
            device buried somewhere unexpected.

       -v   Show version information and quit.

       -h   Display help.

EXAMPLES

       wipe -rcf /home/berke/plaintext/
            Wipe  every file and every directory (option -r) listed under /home/berke/plaintext/,
            including /home/berke/plaintext/.

            Regular files will be wiped with 34 passes and their sizes  will  then  be  halved  a
            random  number  of times. Special files (character and block devices, FIFOs...)  will
            not. All directory entries (files, special files and directories) will be renamed  10
            times  and  then  unlinked.  Things with inappropriate permissions will be chmod()'ed
            (option -c).  All of this will happen without user confirmation (option -f).

       wipe -kq /dev/hda3
            Assuming /dev/hda3 is the block device corresponding to the third  partition  of  the
            master drive on the primary IDE interface, it will be wiped in quick mode (option -q)
            i.e. with four random passes.  The inode won't be renamed or  unlinked  (option  -k).
            Before starting, it will ask you to type ``yes''.

       wipe -kqD /dev/floppy
            Since  wipe  never  follows  symlinks unless explicitly told to do so, if you want to
            wipe /dev/floppy which happens to be a symlink to  /dev/fd0u1440  you  will  have  to
            specify the -D option. Before starting, it will ask you to type ``yes''.

       wipe -rfi >wipe.log /var/log/*
            Here,  wipe will recursively (option -r) destroy everything under /var/log, excepting
            /var/log. It will not attempt to chmod() things. It will however be  verbose  (option
            -i). It won't ask you to type ``yes'' because of the -f option.

       wipe -kq -l 1440K /dev/fd0
            Due to various idiosyncracies of the operating system, it's not always easy to obtain
            the number of bytes a given device might contain  (in  fact,  that  quantity  can  be
            variable).  This  is  why  you  sometimes  need  to  tell wipe the amount of bytes to
            destroy. That's what the -l option  is  for.  Plus,  you  can  use  b,K,M  and  G  as
            multipliers,  respectively  for  2^9  (512), 2^10 (1024 or a Kilo), 2^20 (a Mega) and
            2^30 (a Giga) bytes.  You can even combine more than one multiplier !! So that 1M416K
            = 1474560 bytes.

BUGS/LIMITATIONS

       Wipe  should  work  on  harddisks  and  floppy  disks;  however the internal cache of some
       harddisks might prevent the necessary writes to be done to the magnetic surface. It  would
       be funny to use it over NFS. Under CFS (Cryptographic File System) the fsync() call has no
       effect; wipe has not much use under it anyway - use wipe  directly  on  the  corresponding
       encrypted  files.  Also,  under Linux, when using a device mounted thru a loopback device,
       synchronous I/O does not get propagated cleanly.

       For wiping floppy disks, at least under Linux, there is no way,  besides  obscure  floppy-
       driver  specific  ioctl's  to  determine  the  block  size of the disk. In particular, the
       BLKGETSIZE ioctl is not implemented in the floppy driver. So,  for  wiping  floppies,  you
       must specify the size of the floppy disk using the -l option, as in the last example. This
       option is normally not needed for other fixed block devices, like IDE and SCSI devices.

       File name wiping is implemented since version 0.12. I don't know how efficient it  is.  It
       first  changes the name of the file to a random- generated name of same length, calls sync
       (), then changes the name to a random-generated name of maximal length.

       File size wiping is implemented by repeatedly truncating the file to  half  of  its  size,
       until it becomes empty; sync () is called between such operations.

       Note  that  it is still not possible to file creation date and permission bits portably. A
       wipe utility working at the block device level could be written using the ext2fs library.

AUTHOR AND LICENCE

       Wipe  was  written  by  Berke  Durak  (to  find  my  email   address,   just   type   echo
       berke1ouvaton2org|tr 12 @.  in a shell).

       Wipe is released under the conditions of the GNU General Public License.

FILES

       /dev/random is used by default to seed the pseudo-random number generators.

ENVIRONMENT VARIABLES

       WIPE_SEEDPIPE  If  set, wipe will execute the command specified in it (using popen()), and
       will hash the command's output with the MD5 message-digest algorithm to get a 128-bit seed
       for its PRNG. For example, on systems lacking a /dev/random device, this variable might be
       set in /etc/profile to a shell script which contains various commands such as ls, ps, who,
       last,  etc. and which are run asynchronously in order to get an output as less predictable
       as possible.

SEE ALSO

       open(2), fsync(2), sync(8), bdflush(2), update(8), random(3)