ZIp file CRC

Discussion in 'Computer Support' started by Jonny Smith, Jul 9, 2003.

  1. Jonny Smith

    Jonny Smith Guest

    How can i manually change the CRC on a zip file???
     
    Jonny Smith, Jul 9, 2003
    #1
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  2. Jonny Smith

    dr.p Guest

    "Jonny Smith" <> wrote in news:begmbt$jna$1$8300dec7
    @news.demon.co.uk:

    > How can i manually change the CRC on a zip file???
    >
    >
    >


    You cant without changing the zip file. Its a bit like having 10 numbers
    and asking "how can I change the average of these numbers to the number I'm
    told it should be" - you can't change the average, you have to change the
    numbers which will then make the average change.
    The incorrect CRC is just telling you that the zip is corrupt, so you cant
    "change" the CRC - if possible you will have to get the zip file again.
     
    dr.p, Jul 9, 2003
    #2
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  3. Jonny Smith

    dr.p Guest

    "dr.p" <> wrote in
    news:Xns93B39389F65F9coffemyplace@194.117.158.32:

    > "Jonny Smith" <> wrote in news:begmbt$jna$1$8300dec7
    > @news.demon.co.uk:
    >
    >> How can i manually change the CRC on a zip file???
    >>
    >>
    >>

    >
    > You cant without changing the zip file. Its a bit like having 10
    > numbers and asking "how can I change the average of these numbers to
    > the number I'm told it should be" - you can't change the average, you
    > have to change the numbers which will then make the average change.
    > The incorrect CRC is just telling you that the zip is corrupt, so you
    > cant
    > "change" the CRC - if possible you will have to get the zip file
    > again.


    Or another way of looking at it - theres a big sign on a machine saying
    "this machine does not work", how do I change the sign to say the machine
    does work?

    Changing the sign doesn't make the machine work..
    Changing the CRC doesn't fix the Zip..
     
    dr.p, Jul 9, 2003
    #3
  4. Jonny Smith

    Jonny Smith Guest

    "dr.p" <> wrote in message
    news:Xns93B394D8FF95Ecoffemyplace@194.117.158.32...
    > "dr.p" <> wrote in
    > news:Xns93B39389F65F9coffemyplace@194.117.158.32:
    >
    > > "Jonny Smith" <> wrote in news:begmbt$jna$1$8300dec7
    > > @news.demon.co.uk:
    > >
    > >> How can i manually change the CRC on a zip file???
    > >>
    > >>
    > >>

    > >
    > > You cant without changing the zip file. Its a bit like having 10
    > > numbers and asking "how can I change the average of these numbers to
    > > the number I'm told it should be" - you can't change the average, you
    > > have to change the numbers which will then make the average change.
    > > The incorrect CRC is just telling you that the zip is corrupt, so you
    > > cant
    > > "change" the CRC - if possible you will have to get the zip file
    > > again.

    >
    > Or another way of looking at it - theres a big sign on a machine saying
    > "this machine does not work", how do I change the sign to say the machine
    > does work?
    >
    > Changing the sign doesn't make the machine work..
    > Changing the CRC doesn't fix the Zip..
    >
    >
    >
    >

    Fair enough, but my intention is to corrupt the zip file to test some data
    transfer software. So i want to corrupt the CRC, is this possible???
     
    Jonny Smith, Jul 9, 2003
    #4
  5. Jonny Smith

    dr.p Guest


    > Fair enough, but my intention is to corrupt the zip file to test some
    > data transfer software. So i want to corrupt the CRC, is this
    > possible???
    >




    Not to change the CRC - its calculated from the contents of the zip, so you
    need to change the zip.
    If you want to corrupt the zip then:
    1) copy the zip somewhere first for safe keeping
    2) download a hex editor :
    http://www.chmaas.handshake.de/delphi/freeware/xvi32/xvi32.htm
    that ones freeware and i just used it to corrupt a zip
    3) load the zip file into the hex editor
    4) click on the right hand pane of the window where all the garbage
    characters are (not the left pane with the hex) and type in a load of
    garbage.
    5) save the new improved zip file - its now corrupt.

    what you've done is to change the zip, so it will as a result now have a
    different CRC. Its also corrupt.
     
    dr.p, Jul 9, 2003
    #5
  6. Jonny Smith

    dr.p Guest

    "dr.p" <> wrote in
    news:Xns93B39A550E198coffemyplace@194.117.158.32:

    >
    >
    >> Fair enough, but my intention is to corrupt the zip file to test some
    >> data transfer software. So i want to corrupt the CRC, is this
    >> possible???
    >>

    >
    >
    >
    > Not to change the CRC - its calculated from the contents of the zip,
    > so you need to change the zip.
    > If you want to corrupt the zip then:
    > 1) copy the zip somewhere first for safe keeping
    > 2) download a hex editor :
    > http://www.chmaas.handshake.de/delphi/freeware/xvi32/xvi32.htm
    > that ones freeware and i just used it to corrupt a zip
    > 3) load the zip file into the hex editor
    > 4) click on the right hand pane of the window where all the garbage
    > characters are (not the left pane with the hex) and type in a load of
    > garbage.
    > 5) save the new improved zip file - its now corrupt.
    >
    > what you've done is to change the zip, so it will as a result now have
    > a different CRC. Its also corrupt.
    >
    >
    >


    Hmm, looks like the zip stores the crc inside itself. The CRC must be from
    the original files. I altered the crc stored in the zip, and it resulted in
    a corrupt zip, which couldn't be repaired successfully by winrar (winrar
    handles zips too).
     
    dr.p, Jul 9, 2003
    #6
  7. Jonny Smith

    Jonny Smith Guest

    "dr.p" <> wrote in message
    news:Xns93B39CBF3B94Ccoffemyplace@194.117.158.32...
    >
    > > Hmm, looks like the zip stores the crc inside itself. The CRC must be
    > > from the original files. I altered the crc stored in the zip, and it
    > > resulted in a corrupt zip, which couldn't be repaired successfully by
    > > winrar (winrar handles zips too).
    > >

    >
    > - so I was wrong and you can alter the CRC. Do you still want to do this?
    >


    If you could give me instructions on doing this then that would be
    excellent, thank you
     
    Jonny Smith, Jul 9, 2003
    #7
  8. Jonny Smith

    swapnilll

    Joined:
    Oct 26, 2012
    Messages:
    1
    Dont need to change CRC no.

    Follow the steps given below to open the file giving the error "CRC no. does not match". I had done it with WinZip 17.0.10283 (Evolution copy). You may find it on FileHippo.com
    1)Open the file with WinZip.
    2)Then Right Click on selected file in WinZip.
    3)Select the option "new zip file(from selected files)".
    4)A new window will open.
    5)set its type as".ZipX".
    7)Select folder location.
    8)After some time, you will got an message about "error".
    9)You just have to do is to select the option "continue".
    10)Then a new .ZipX file will be created at selected location.
    11)Again, you have to extract this file with WinZip.
    12)And the Job is done...
    Have fun!!!!!:D
     
    swapnilll, Oct 26, 2012
    #8
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