[Scottish] Recursive MD5 sums

Calum Matheson cbm at gmx.co.uk
Mon Sep 6 19:25:08 BST 2004

Hello Allan,

I'd think that it's impossible.

From the MD5 homepage at
http://userpages.umbc.edu/~mabzug1/cs/md5/md5.html :

> It is conjectured that it is computationally infeasible
> to produce two messages having the same message digest,
> or to produce any message having a given prespecified
> target message digest

A given prespecified target digest would be what is required.

So it's computationally infeasible, if still theoretically possible -
as for the algorithm that would be required, I've absolutely no idea!

(It might be that some MD5 programs ignore RCS tags - so you could
insert the pre-calculated hash inside them - I'm sure that would be
cheating though :) )


Monday, September 6, 2004, 3:54:04 PM, you wrote:

AW> Hi,

AW> Is it possible to have an md5sum quoted in a file which corresponds to the
AW> md5sum of that file?

AW> I guess that this will either be a really trivial thing to do or it'll be
AW> one of those silly npc (or whatever it is) problems.

AW> Links or explantions of algorithms and/or implementations would be
AW> interesting (I'm more asking out of interest than anything else).

AW> Thanks,

AW> Allan

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Best regards,
 Calum                            mailto:cbm at gmx.co.uk

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