Lazarus
Free Pascal => Beginners => Topic started by: TomTom on August 14, 2019, 01:06:39 pm
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Hi :)
I have many files that need to have their checksums changed. How can I do this? Is this even possible?
These are tif images. I know I could add single pixel at random position and checksum will change but Im wondering if there is some more elegant way (not changing image).
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A checksum is a derived statistic.
Unless the binary representation of the file changes in some way, its checksum will not change (unless the checksum calculation algorithm is substandard).
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So... I need to change something in the file like in my case, set random pixel to random color for example.. or change some meta-data... Am I right?
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Some checksums have certain properties. E.g. you make the file 4 bytes longer to n+4, and take the checksum of the first n bytes, and craft a value to put in the four extra bytes so that the value over n+4 bytes is what you want.
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If the hash is over the full TTiffIFD record, you can possibly modify the date, or one of the document properties, like the model of the scanner 8-)