code: func recoverNodeKey(hash, sig []byte) (key encPubkey, err error) {
  	pubkey, err := secp256k1.RecoverPubkey(hash, sig)
  	if err != nil {
  		return key, err
  	}
  	copy(key[:], pubkey[1:])
  	return key, nil
  }
docs: // recoverNodeKey computes the public key used to sign the
  // given hash from the signature.