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Is there a way to make a small text file produce an md5sum of all 0's. Or any easy testable string that the likes of perl could test with. sha could be used if that gives me the result I am after, to simple have a file on my removable storage devices that tells me its mine and what it is. Ian

Ianox
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    Sorry, but I have no clue what you want. The first sentence looks like you want to find out what file would preduce an md5sum of all 0's. But everything after that is confusing. Are you asking on how to find the origional string from an md5sum or SHA, (or probably: a collision) ? – Nanne May 25 '11 at 11:03
  • I don't quite understand your question, it may help to rephrase it. (Text files don't produce anything, and I don't know what you mean by a file that tells you it's yours. When you say "an md5sum of all 0's", do you mean the output is 128 zeros or the input is a string of unspecified length where each character is `0`?) – Andrzej Doyle May 25 '11 at 11:03
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    Rainbow tables might be what you're looking for? – Flexo May 25 '11 at 11:21

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The whole point of MD5, SHA and other cryptographic hashes is to make it really really difficult to find a text producing a given hash. I don't understand what you want to do, but finding a small text file producing an MD5 of all 0's is not possible. If it were, MD5 would be broken.

JB Nizet
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  • Ummm - got the question wrong. What can be done inside the text file to influence the md5sum string, so the md5sum will produce a known string? – Ianox May 27 '11 at 10:43
  • I have a small text file on the root of each of my removable storage devices. The file name tells me what my device is. All the files contents are always the same, so I can md5sum them to tell me I am right in saying this is my device. Problem is I cannot change the content of this file to tell me a bit more about it. So, is there a string I can include in the text to make a known md5sum result? – Ianox May 27 '11 at 10:50
  • I have a small text file @ top of my removable storage devices. File name tells me what my device is. Contents are always the same, so I can md5sum them to tell me I am right in saying its my device. Problem - I cannot change the content of this file for a bit more info about it. So, is there a string I can include in the text to make a known md5sum result? The very first hard disc (4meg) I think, had the second byte of each sector a value that when the whole sector was summed, it = zero. Easy hardware logic to test each sector as it came off the disc. Ianox – Ianox May 27 '11 at 11:01