[ale] OT: MD5 checksums & math

[Benjamin Scherrey]

Unfortunately this cannot be done as the MD5 key generated is a hash result and
may be generated by an infinite number of possible combinations (i.e. collisions
can occur). If what you proposed were possible then you would also be able to
extract out exactly what the contents of X was simply from the contents of the
MD5 key of A & B! That data simply does not exist here to be extracted. Talk
about the greatest form of data compression! :-) Such a key can only be treated
as a signature which is difficult (but not impossible) to forge.

    later,

        Ben Scherrey

Randy Janinda wrote:

> 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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