What is MD5 Hash?

Discussion in 'A+ Certification' started by Kenny, Nov 18, 2003.

  1. Kenny

    Kenny Guest

    I know it's something added to a file when it's created and have found a few
    definitions using Google but I still don't understand it! Is it a form of
    error detection/correction and why is it used? Can someone explain it in
    layman's terms please?


    --

    Kenny
     
    Kenny, Nov 18, 2003
    #1
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  2. Kenny

    dave Guest

    Kenny wrote:
    > I know it's something added to a file when it's created and have found a few
    > definitions using Google but I still don't understand it! Is it a form of
    > error detection/correction and why is it used? Can someone explain it in
    > layman's terms please?
    >
    >
    > --
    >
    > Kenny
    >
    >
    >





    http://linux-sxs.org/security/md5sum.html
     
    dave, Nov 19, 2003
    #2
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  3. Kenny

    Ghost Guest

    In article <3fba6ff6$>, "Kenny"
    <> wrote:

    > I know it's something added to a file when it's created and have found a few
    > definitions using Google but I still don't understand it! Is it a form of
    > error detection/correction and why is it used? Can someone explain it in
    > layman's terms please?
    >
    >
    > --
    >
    > Kenny


    No, it is not something "added to a file"...

    We use this in forensics heavily- but it is also used by software
    manufacturers to ensure authenticity.

    It is a security program. What it does is calculates a hex value for the
    file, directory, or even the entire drive. If any portion of that file,
    directory, or drive is changed in even the smallest way- the calculated
    sum will be different.

    In forensics, before I examine a drive, I would run a hash on it,
    returning a 128 bit calculation. This is then recorded in my logs. Then,
    when I am finished with the examination, I would run a hash again. The
    calculated number must match EXACTLY. This gets logged as well. This
    proves I did not alter any data whatsoever, even by accident. This must
    be repeatable by any other examiner, who must get the same calculated
    result.

    If there is even the slightest hint of a change- one bit changed- then the
    calculated number will be completely different- not even close.

    For sofware manufacturers, it helps ensure that whatever you are
    downloading is the actual, original software as manufactured, and not
    altered or hacked in any way. You will find on some download areas,
    especially stuff for security, that they will publish a hash. You can run
    your hash program (typically MD5) and should get the same results as what
    is published. You now know you have the correct file without alteration
    or hack.
     
    Ghost, Nov 19, 2003
    #3
  4. Kenny

    RussS Guest

    MD5 is an algorithm

    Source ... http://www.faqs.org/rfcs/rfc1321.html

    This document describes the MD5 message-digest algorithm. The
    algorithm takes as input a message of arbitrary length and produces
    as output a 128-bit "fingerprint" or "message digest" of the input.
    It is conjectured that it is computationally infeasible to produce
    two messages having the same message digest, or to produce any
    message having a given prespecified target message digest. The MD5
    algorithm is intended for digital signature applications, where a
    large file must be "compressed" in a secure manner before being
    encrypted with a private (secret) key under a public-key cryptosystem
    such as RSA.
     
    RussS, Nov 19, 2003
    #4
  5. Kenny

    Kenny Guest

    Thanks for the replies.

    --

    Kenny


    "Ghost" <> wrote in message
    news:user-1911030039450001@1.0.0.101...
    > In article <3fba6ff6$>, "Kenny"
    > <> wrote:
    >
    > > I know it's something added to a file when it's created and have found a

    few
    > > definitions using Google but I still don't understand it! Is it a form

    of
    > > error detection/correction and why is it used? Can someone explain it

    in
    > > layman's terms please?
    > >
    > >
    > > --
    > >
    > > Kenny

    >
    > No, it is not something "added to a file"...
    >
    > We use this in forensics heavily- but it is also used by software
    > manufacturers to ensure authenticity.
    >
    > It is a security program. What it does is calculates a hex value for the
    > file, directory, or even the entire drive. If any portion of that file,
    > directory, or drive is changed in even the smallest way- the calculated
    > sum will be different.
    >
    > In forensics, before I examine a drive, I would run a hash on it,
    > returning a 128 bit calculation. This is then recorded in my logs. Then,
    > when I am finished with the examination, I would run a hash again. The
    > calculated number must match EXACTLY. This gets logged as well. This
    > proves I did not alter any data whatsoever, even by accident. This must
    > be repeatable by any other examiner, who must get the same calculated
    > result.
    >
    > If there is even the slightest hint of a change- one bit changed- then the
    > calculated number will be completely different- not even close.
    >
    > For sofware manufacturers, it helps ensure that whatever you are
    > downloading is the actual, original software as manufactured, and not
    > altered or hacked in any way. You will find on some download areas,
    > especially stuff for security, that they will publish a hash. You can run
    > your hash program (typically MD5) and should get the same results as what
    > is published. You now know you have the correct file without alteration
    > or hack.
     
    Kenny, Nov 19, 2003
    #5
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