Convert ppk to OpenSSH keypairs

.ppk files are created by PuTTY to store a private key generated by the program.

To convert keypairs, first you need to install the package putty and then:

Generate the private key:

puttygen id_rsa.ppk -O private-openssh -o id_rsa

Generate the public key:

puttygen id_rsa.ppk -O public-openssh -o id_rsa.pub