Is it possible to calculate a public key from the message hash and signature?

Question

Is it possible to calculate a public key from the message hash and signature?

Answer 1

It is possible to create a public key from the signature. It will be equivalent to the key used to generate the signature but not necessarily identical.

You can find an example implementation here.

Answer 2

BIP143 implies it is possible per the No FindAndDelete example.

I think the following pseudocode would do it

pubkey = get_pubkey(generate_key())
while not verify_sig(signature, pubkey, msg_hash):
  pubkey = get_pubkey(generate_key())

and as David suggested, I suppose not necessarily identical but equivalent for signature verification purposes.