Convert PPK files to OpenSSH keys

PPK files are generated by PuTTY, but cannot be used with plain ssh command in Linux terminals.

To convert these files to "standard" format (OpenSSH keys) you need to use the puttygen command:

puttygen ppk_file.ppk -O private-openssh -o ~/.ssh/from_ppk
puttygen ppk_file.ppk -O public-openssh -o ~/.ssh/from_ppk.pub

Then, you can use it:

ssh -i ~/.ssh/from_ppk user@random_ip