I wonder if Q meant for us to find this information:
https://wikileaks.org/vault7/#Hive
https://wikileaks.org/vault7/document/Angelfire-2_0-UserGuide/
These are some of the C_A wikileaks exposing their tools–specifically the Angelfire suite, which targets Windows computers. "Keystone" is one of the five components. The explanation of how it works is in pic related.