The possibility of finding two lumps of random garbage, even with equal length, has *always* been a given with any mechanism that represents a larger range of possible inputs with a smaller range of possible outputs.

With an input space of 128²⁵⁶ = 2790951116e530

And an output space of 2¹²⁸ = 3.4e38, it could not be otherwise. There have to be at least 8 inputs for every output.

Maybe you missed the emphasis I placed in my post?

The effect is to considerably increase the difficulty of finding an alternative text that matches both the outer and inner md5 and renders a useful (to the bad guy), alternative text.

To generalise my challenge in the way you suggest would be to ignore the point I was trying to make, and that ikegami partially made subsequent to his first post--

• it's one thing to brute force two texts with the same md5.
• It is an entirely different scale of problem to find a second text that has the same md5 as some existing text.
• Much harder still to generate a second text, that say's something meaningful and useful that has the same md5 as an original text (derived from a 3rd party source).
• And finally, generating a second text, that is meaningful and useful to your nefarious purpose, that satisfies the criteria of have the same md5 as the original 3rd party text when it own md5_hex digest is concatenated to it.

Each of those requirments has a multiplier effect upon the difficulty of the task at hand for the bad guy. It is this same multiplier effect that stuff like double-DES and triple-DES exploit for their greater security.

So sorry, but your gonna have to work a little for that free lunch :)