"With a single round of hashing, there are two possible inputs A1 and A2 that can produce the final output O."
No, there is an infinite number of inputs that produce the final output O. And you have to find something that produces O after exactly n rounds of hashing, it doesn't help to find something that produces O after one or two rounds.
Edit: Sorry, didn't see your assumption when I first posted, but I guess what I said will be true for all relevant hashing functions.
No, there is an infinite number of inputs that produce the final output O. And you have to find something that produces O after exactly n rounds of hashing, it doesn't help to find something that produces O after one or two rounds.
Edit: Sorry, didn't see your assumption when I first posted, but I guess what I said will be true for all relevant hashing functions.