[ale] OT: MD5 checksums & math

[Robert Butera]

On Mon, 17 Jul 2000, 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

Definitely not for the weak!

Looking at the MD5sum algorithm at

ftp://ftp.isi.edu/in-notes/rfc1321.txt 

I would "guess" that the answer is no. It is nowhere near as straigtforward
as a checksum algorithm.

However, it _might_ be _possible_ to describe some sort of "transformation"
from image A to image B that could then be applied to image C to get image
D.  It would also be a lot of work to derive such an operation.  This
is something you'd have to consult someone with a serious degree of 
mathematical knowledge in either cyptography or communications -- they
know how to at least tackle such problems.



Robert Butera, Assistant Professor
School of Electrical and Computer Engineering
Institute for Bioengineering and Biosciences	
Georgia Institute of Technology, Atlanta, GA, 30332-0363 USA
--> http://www.ece.gatech.edu/users/rbutera/



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