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Thread: Self-referential checksum

  1. Mar 18th, 2007, 12:10 AM #1
    agent
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    Self-referential checksum

    I have a need for two or more files to contain checksums (say, MD5) of each of the other files, such that if any one file changes, the other files will contain the old (thus incorrect) checksum.

    How might I do this?
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  2. Mar 18th, 2007, 05:12 AM #2
    Hack
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    Re: Self-referential checksum

    No development platform specified so unsure where to move this.

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  3. Mar 19th, 2007, 02:24 PM #3
    Al42
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    Re: Self-referential checksum

    You usually don't use include checksum portion of a file in the checksum. i'd suggest that you do the same thing - reserve as many bytes as you need for the checksum, then checksum the rest of the file.

    If you're talking about each file just being the checksum of the other, you have what's known in hardware as a race condition, and in cartography as "you can't get there from here". In informal circles, you're said to be SOL.
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  4. Mar 19th, 2007, 03:07 PM #4
    agent
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    Re: Self-referential checksum

    hmm... thought so... ok. now onto plan b, as stated above by somebody else...

    What I really wanted to do was be able to detect if somebody was trying to change the checksum itself in one of the files.
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