No, public key cryptography means that the key doesn't need to be shared.
A blockchain is only needed if parties need to write to the database in a decentralized manner, and the order of the writes is important & can't be tampered with.
Of course. The OP didn't mention which key, so assumed they are talking about the private key, especially when they mentioned out-of-bound sharing, usually terminology used for asymmetric cryptography. Public keys don't need to be shared out-of-band, in fact they are always published along with the transaction on the blockchain. (well technically, only the curve points and the hash are, but using these, we can re-create the public key)
Comments
What is the proof? That the domain owner signed it with a certain key? Is that key shared out-of-band? If so why do we even need the blockchain?
Yes, the proof would be some sort of signature.
No, public key cryptography means that the key doesn't need to be shared.
A blockchain is only needed if parties need to write to the database in a decentralized manner, and the order of the writes is important & can't be tampered with.
The public key still needs to be shared.
Of course. The OP didn't mention which key, so assumed they are talking about the private key, especially when they mentioned out-of-bound sharing, usually terminology used for asymmetric cryptography. Public keys don't need to be shared out-of-band, in fact they are always published along with the transaction on the blockchain. (well technically, only the curve points and the hash are, but using these, we can re-create the public key)