def to_point
      p = pubkey
      p ||= generate_pubkey(priv_key, compressed: compressed)
      ECDSA::Format::PointOctetString.decode(p.htb, Bitcoin::Secp256k1::GROUP)
    end
def to_point
      p = pubkey
      p ||= generate_pubkey(priv_key, compressed: compressed)
      ECDSA::Format::PointOctetString.decode(p.htb, Bitcoin::Secp256k1::GROUP)
    end
generate pubkey ec point
 @return [ECDSA::Point]