And the main feature of sha256 hex pvt key that makes it secure in the first place is, once you change even one letter in (input) string, the entire hex output changes! This works both way, if you change the output (the sha256 32 byte) , the input will be hugely different. And to make things even harder, that's just one hash function, now let's continue the process of generating the address: we're doing ripemd of the sha256 of the resulting pub key to get the address .. By design, this means that whatever comes out as an address will change significantly after all that hashing we went through. This means that you can have trillions and trillions of addresses starting with 13zb1hQ.... Spread around the entire 256 bit range leaving you with the fact that none of them is the exact address you're looking for. Someone then might ask then why would we search by prefix instead of addresses?! The answer is simple: it's way faster to look for part of the address. That's the only advantage. But It doesn't say anything about determining the range.