code: func IsValidKeyJson(j []byte) []byte {
  	j1 := new(keyJSON)
  	e1 := json.Unmarshal(j, &j1)
  	if e1 == nil {
  		addr, _ := hex.DecodeString(j1.Address)
  		return addr
  	}
  	return nil
  }
docs: // returns the address if valid, nil otherwise