group key的用法和样例：
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.
摘要多播安全要确保所有参加多播的成员安全地共享同一组密钥，当有成员加入或离开时需要及时更新组密钥。 - 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.
这组密钥，必须同从护照上光感条码扫描到系统里的一串数据生成的另一组加密密钥相匹配。
