Quote from: NotATether on Today at 06:16:56 PM

Quote from: mynonce on October 29, 2021, 11:48:38 PM

Can you sign a message with that public key?

In the OP example there is a valid signature. That means someone has (or had) the private key for the public key.

You cannot sign messages unless you have the private key (which you do not have in your example).

In the OP example there is a valid signature, as I said. That meant, that the creator has the private key. And we wondered how that is possible.

pooya87 solved it:

Quote from: pooya87 on October 30, 2021, 07:00:28 AM

Rather simple.
You start in reverse meaning instead of adding random public keys to the starting pubkey, you find the final key and then start working your way backwards by subtracting the pub key (of the private key you already have) from the starting public key (which you don't have the private key of).

...

I will use 3 keys in total to keep the computational cost to minimum since I don't want to waste my time but the idea is the same

...

1. C (from origninal pubkey posted above).
2. W (what we want to get in the mid pubkey). Call this pub2
3. Random letter that doesn't matter.

Code:

LOOP:
Compute pub2 = pubX - pub1
Compute address of pub2 and check if it starts with W
return if true
change privX to privX+1
END;

In short:

The creator has only the private key for the signature address 17mZRodKy5ufNqJVsyKg1bEt81AnRkkh9L.
All other Bitcoin addresses are calculated with public keys and the creator doesn't have the private keys.