PuTTYgen is a key generator tool to generate SSH keys. It can also convert file from one format to another.
What is a Pub File?
A pub file is an extension of a public key. It is used to establish a connection with remote desktop. It can be shared on the server for authentication. The Public key helps to find the user identity.
What is a PPK File?
It stands for PuTTY private key. Private key stored in .ppk format. It is necessary to keep private key secure. It cannot be shared with everyone.
Convert .pub to .ppk file
It is not possible to convert .pub file to .ppk file because PuTTYgen could not support the public key to convert it into .ppk format.
We can also show proof of this:
First, we have to generate public and private key by using OpenSSH.
Open the PuTTYgen, Go to Start Menu>All Program>PuTTY>PuTTYgen
In PuTTYgen Terminal Click on load a locate the generated public key. Then click on open
As you can see it could not support public key. But both the public key and private key can be used for securing communication and authentication. Private key proves your identity and Public key verifies your identity. Hence, it is not possible to convert .pub to .ppk file.