Given that hash codes inherently allow multiple inputs to generate the same output, this is a far less demanding problem.
Not simple, not trivial, not straightforward, but in the realm of possibility.
Especially if you know the algorithm used to generate a given provider's hash.
Absolutely. From later posts, it's obvious that you understand this better than your initial message indicated to me.
This is why I really dislike use of MD5, though it is good for examples. I recall someone being able to successfully generate some email message collisions quite a while back. Even SHA1 has some known weaknesses. sha256 should leave you outside of any reasonable likelihood of collision this side of the sun's eventual death by nova.
OK. so, here's another thought that's almost completely off topic, but not quite...
Let's say Alice makes claims on the internet to have built a spaceship that contains a functional time machine in it. (A time machine without an accompanying spaceship is pretty useless for obvious reasons)
Bob reads about those claims and is rightfully sceptical. "Prove it" says he.
Alice agrees and posts something that looks like this...
Today is 7/26/2013 b4a551c8edf7f28a19353f95a74275af46bf620165d85e11032b165f188d22aa I'll post again on 7/28/2013
On the 28th, she posts:
Today is 7/28/2013 echo "07/27/2013 25 32 35 50 51 MB: 46" | sha256sum QED
Would you say that could suffice as proof?
Beats me! Mongo just pawn in game of life...