So I've seen many many posts on how to do the conversion with private key; but does anyone one know how I can do this with just only public key? As I'm trying to convert someone else's public key.
Or is this something not possible and I need to ask them to generate one themselves?
If you are just looking to convert a public key, not create a certificate then you only need the public key.
ssh-keygen -f id_rsa.pub -e -m pem > id_rsa.pub.pem
Will read a public key file id_rsa.pub (containing just your friend's public key) and convert it to pem format.
The private key would be needed for something like a self signed certificate (in x509 format) because it's the private key that generates the signature.
