code: def crypto_sign_open(signed, vk):
      
      if len(vk) != PUBLICKEYBYTES:
          raise ValueError("Bad verifying key length %d" % len(vk))
      rc = djbec.checkvalid(signed[:SIGNATUREBYTES], signed[SIGNATUREBYTES:], vk)
      if not rc:
          raise ValueError("rc != True", rc)
      return signed[SIGNATUREBYTES:]
docs: Return message given signature+message and the verifying key.