[ale] OT: MD5 checksums & math

Douglas Bridges doug_bridges at hotmail.com
Mon Jul 17 14:54:47 EDT 2000


No, you cannot predict the outcome. MD5 sum does some pretty nasty 
transforms bitwise to the info. The algorithm it uses is not transative as 
far as I can tell. If you want to look at the spec and a reference 
implementation, check out http://www.faqs.org/rfcs/rfc1321.html.

Doug Bridges

>From: Randy Janinda <randy.janinda at ndcorp.com>
>To: Atlanta Linux Enthusiasts <ale at ale.org>
>Subject: [ale] OT: MD5 checksums & math
>Date: Mon, 17 Jul 2000 14:37:51 -0400
>
>Not for the meek hearted:
>
>Let me try to explain this request.
>
>I have four images. I know the md5sum of three of them and I want to
>predict the md5sum of the fourth.
>
>Here's the facts:
>
>ImageA is the same as ImageB except on minor addition to ImageB (we'll
>call this addition X).
>
>md5sums:
>
>ImageA = c76ada9f51c10ee6ccbc9bccd2e05358
>ImageB = 53485d8e8171766b533d13d2df0ffa97 (ImageA + X)
>ImageC = b64a84171c956e14aab561b1545cbc70
>
>Now assuming ImageD has the same exact addition as ImageB (the X
>factor) can I predict the md5sum by adding that "X" factor to ImageC?
>
>ImageD = ImageC + X
>
>
>Is that clear enough? Does anyone have any ideas?
>
>Thanks,
>Randy
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