By default Amazon provides a PEM file to connect to AWS components. These .pem files will not allow you to connect on Windows when using Putty client which is the most widely used SSH client. To be able to connect to Amazon we need to convert the .pem file to a .ppk file using the following

Download puttygen from the following location - http://the.earth.li/~sgtatham/putty/latest/x86/puttygen.exe

Run the executable and the above window pops up. To convert an amazon key to a PuTTY key, use the menu option Conversions ? Import Key. Load the .pem file that you downloaded and press the Save Private Key button.

It will warn you about leaving the passphrase blank. That’s ok.

Save the file to the location that PuTTY has been configured to look in for it’s keys.

Now you can connect to your EC2 instances using the .ppk file you just created.