Quote from: o_e_l_e_o on Today at 10:23:05 AM

Quote from: Jason Brendon on Today at 10:07:12 AM

Will there be two different input producing the same hash result? (hypothetically, a 200-bit input entropy produces the same hash result of 20000bit...)

If you are generating private keys by using SHA256 on different inputs, then yes. Indeed, there will be many more than two inputs which will result in the same output.

For SHA256, you must append to the end of your input the length of that input expressed as a 64 bit number. This places an upper bound on the length of the input, which will be 2⁶⁴ - 1 bits. For reference, this means that any data up to approximately 2 exabytes (2 million terabytes) in size could be used as in input to SHA256, if you had the hardware capable of processing it. Given this, and given that we know that SHA256 will always produce a 256 bit output, then it is easy to see that there will be many billions of inputs which must map to the same output.

There are no known collisions for SHA256, however. If you manage to find two different inputs which hash to the same output, then there is a 0.27634251 BTC bounty you can claim as a reward:
REWARD offered for hash collisions for SHA1, SHA256, RIPEMD160 and other
https://mempool.space/address/35Snmmy3uhaer2gTboc81ayCip4m9DT4ko

Okay.Thank you for your answers. So, if i understand you right, what you mean is that there will be collisions and the collisions will be more than two. But even there will be collisions, it is not very likely to happen.

Yes, i am sure it is not likely to happen. But with quantum computers in place... i don't know if i shall worry. Sure it is not happening right now, but technology is rapidly improving..