There's no difference between SHA256(PubKey) and SHA256(PrivKey).
By the way adding salt would be better since bruteforcing SHA256(PrivKey) is much easier than bitcoin directly.
So, SHA256(PubKey) or SHA256(PrivKey+salt) are both safe.

What do you need SHA256(privkey) for? If you don't know the privkey how do you know he has it?

With SHA256(pubkey) you can calculate the BTC address (ripemd160 + checksum) and verify that he actually has the pubkey, and if he has the pubkey he also has the privkey.

I think that is the only way to prove that someone has the key before the transaction is made and without exposing the pubkey.

Ok, first try to quote properly to avoid unnecesary sub-quotes.

I am going to add some previous comment that I already did:


Even 5% for me is OK

But as i write before, the only ways to perform securely that Transactions are:


Anyone with a little of knowlege can use the Marathom Slipstream service, So i don't see the point to request do that to someone else.

No, I mean if he could transfer puzzle #66 to his own wallet using RBF, bsgs method …
Would he return 90% of the reward to the real finder? (The one who proves ownership by sharing sha256 of publickey or privatekey before broadcasting the first transaction)

Maybe he tries to sell the key with a discount. That is a different situation, it is not just help to copy-paste. It is about the risk of failure.

Then, it is "mining pool vs mining pool". Reorging a single block is not that easy. First, the block will quickly propagate across the whole network, so a lot of major pools will be mining on top of the earliest one. And second: successfully mining a single block is not enough to reorg the chain. You would need to mine two blocks: one on the same height, and another one, on top of it, to actually trigger a chain reorganization.

Also, it is possible to check on testnet, how hard it is to reorg a single confirmation (especially, if a block is ASIC-confirmed). Sending 9950 tBTC in fees was not reverted, even though the block was CPU-mined. I don't know exactly, which amount would be big enough, to get it reorged, but I am accumulating test coins, to test that kind of scenarios.

Edit: More than that: small pools have too low hashrate, to succeed at such attack. And big mining pools have too much reputation to lose, because if some pool will attack, then by looking at chaintips, node runners could prove, that "the pool named X stole those coins". And then, you can imagine, how many miners will switch to a different pool in that case.

So, full-RBF is applied only to transactions, not to the whole blocks. In case of blocks, it is first-seen. And you need two blocks, to trigger a reorg, a single block is not enough, because first-seen block will be different in 99% of mining pools, so they will extend the original chain.

To prove that key has been found, an easy and reliable way to confirm this could be for the finder to make a transaction to the respective pk ETH address and then make a withdrawal. This way I believe I think doesn’t compromise key in any way. At this point I would start to take all this seriously.

Edit_
After some research… Is there a way to check equivalent BTC-ETH address without any privkey risk?

Do anyone really win in these puzzles?
I don’t follow up on these puzzles because, it’s always a hard to agree if someone would sell a wallet that is worth so much for less. Maybe am missing something here but, what stops the individual from trying to do it themselves and own whatever is on it. Except there is nothing on it which wouldn’t surprise me very much or perhaps, you never get to solve the puzzle. Are there people to have solved a few of these here?

Crypto users don't trust, they verify, so unless you provide a way to support your claims, your post means absolutely nothing.