Key - ppk key format
About
private key PuTTY storage format.
PuTTY stores keys in its own format in .ppk files.
Management
Create
PUTTYGEN - KEY GENERATOR FOR PUTTY ON WINDOWS
Start menu → All Programs → PuTTY→ PuTTYgen.
Click Generate, and start moving the mouse within the Window. Putty uses mouse movements to collect randomness. As you move it, the green progress bar should advance.
Specify a
passphrase for the key if keys are
NOT needed for automation (e.g., with WinSCP)
Save private key.
Save the public key (It can be later regenerated by loading the private key by clicking Load).
then see : Key usage
Documentation / Reference