A friend asked me if she can just create a new address in her hw wallet, will it be secret address? Or is it likely coinanalys or some bitcoin server would be able to link that new address to all the other ones inside the hw wallet?
Central servers do not just know only your addresses but also your IP addresses and that can help in knowing other wallets.
What i was thinking about is if its possible for a bitcoin address to be reversed to the public key? And then that public key reversed to see which xpub created it? I remember reading something about that.
I know it's not possible to know which master private key created the xpub but I don't know about the other things. Because if you can with an address do some algorithm to see which xpub it comes from, then you can find out all the other addresses that the xpub has created. Is any of this possible?
Using a passphrase might be helpful in this situation, it helps you generate different wallet addresses even with the same seed phrase, but the best option is if you are buying a hardware wallet, don't buy from a secondary seller, buy directly and get it shipped to your house address. That's the best way to avoid any loopholes regarding this. Creating multiple seed phrases just to avoid these kinds of situations is not helpful; scammers are smart asses every day.
Can I without worry share my seed phrase publicly online if I only use a hidden wallet which uses a strong passphrase?