The article (as I understand it) discusses that by default, your SSH private key passphrase is essentially just a glorified MD5 hash, which is relatively easy to brute-force due to the speed at ...

putty uses a different key format than openssh. You'll have to generate a new keypair using the ssh-keygen command in linux and append the public key to your authorized_keys file.

In them they found over 580 unique private keys for SSH and HTTPS, many of them shared between multiple devices from the same vendor or even from different ones.