At a very early stage it may be possible to get to the encryption key, not at a later stage.
How you got infested?
1. hidden installation along with other apps, especially the utilities that work as freeware or shareware;
2. dubious link in spam emails leading to the virus installer
3. online free hosting resources;
4. using illegal peer-to-peer (P2P) resources for downloading pirated software.
polonus