What's master key in hive metastore?

[Xi Chen]

Dear all,

I find several APIs about master key in hive metastore and
IMetastoreClient. I searched around but didn't find any usage in hive DDL
tasks. Any idea where this master key is designed for?

Thanks in advance,
bargitta

int addMasterKey(String key) throws MetaException, TException;

void updateMasterKey(Integer seqNo, String key)
    throws NoSuchObjectException, MetaException, TException;

boolean removeMasterKey(Integer keySeq) throws TException;

String[] getMasterKeys() throws TException;