group key的用法和樣例：
例句
- Multicast security ensures that all members of a multicast group share the same set of keys safely and when some members join or leave, new keys must be updated.
摘要多播安全要確保所有參加多播的成員安全地共享同一組密鑰，當有成員加入或離開時需要及時更新組密鑰。 - This has to match another encrypted key that is generated from a string of data scanned into the system from the optical bar-code printed in the passport.
這組密鑰，必須同從護照上光感條碼掃描到系統里的一串數據生成的另一組加密密鑰相匹配。
