Generate .ppk out of .pem with Linux (Ubuntu)

Here is a example how to convert .pem to .ppk using Ubuntu.

First you need to install package putty-tools

 sudo apt-get install putty-tools  

After install, all you really need to do is this:

 puttygen key.pem -o key.ppk  

But.. with -P switch you can set passphrase for extra security, this is recommended and easy to do:

 puttygen key.pem -o key.ppk -P -C "My server key"  

It is also recommended to set comment for your key using -C switch, because this string will be prompted to you when you are entering your passphrase.

Note that you can also change passphrase afterwards by using -P switch

 m@box:~/Downloads$ puttygen -P key.ppk   
 Enter passphrase to load key:   
 Enter passphrase to save key:   
 Re-enter passphrase to verify:   

And you are done!

Generate .ppk out of .pem using PuTTYgen

First you must download PuTTYgen, you can download it from here.

Open PuTTYgen and select Load

Note that you must select All Files (*.*) from filter or you cannot locate the file. Click Open 

Next up "Save private key" should no longer be greyed out, click it and name your .ppk file.

And you are done!