Reference: Beyond FTP Private Key Management
This window displays the key values associated with the selected Key Name. The displayed key values are NOT the actual keys. They are generated from the key using industry standard operations, and allow you to check whether two different installations really do share the same key information.
The primary key is the currently active key. It is the first key to be used. The secondary keys allow remote installations to connect for a period of time after the primary key is changed. This allows you to propagate key changes in an orderly manner, either manually or through the key client/server process.