For years I've known about and used SSH with keys to automate login. I've always simply used the ssh-keygen and copied the public key into the authorised keys wherever I needed to log in into.

A couple of months ago I started with AWS and they have a thing called key pairs, which I am sure is closely related to the keys that I know.... but it isn't exactly the same thing. These strange keys do work - I can use them as per the instruction on EC2, but not the same way I'm used to.

Could someone explain to me the difference, and more specifically what the .PEM file is that works with the -i flag in SSH. What is the advantages of the one over the other, etc.

I've now taken to adding the normal kind of keys to my EC2 instance user authorised_keys files since I know it better... and could not find a way to automate dolphin and scp and most other tools (I could only get ssh itself to work with the PEM file)

I have not yet managed to hit the right google search terms so my knowledge and understanding of PEM is still near nil.