Enable strong private key protection.

启用强私钥保护。

Third, comprehensive defense, key protection.

第三，全面防御，重点防护。

There are several possibilities of key protection.

有几种关键保护的可能性。

Differential relay is the key protection for power transformer.

差动保护是变压器的主保护。

Old courtyard is now listed as key protection units in Hunan Province.

老院子现列为湖南省重点文物保护单位。