chmod unable to change permissions

I'm facing an annoying problem. It's been pretty frustrating. I am using a computer at my school to work on the Coursera Startup class. I am trying to connect to an Amazon EC2 instance. I downloaded the key pair. I check permissions.

mac5-library:startup roh21$ ls -ltotal 6-rw-rw-rw-@ 1 roh21  108  1692 Jun 22 16:45 startup-class-key.pem

So, it's not secure. So I need to change the permissions. I try:

mac5-library:startup roh21$ chmod 400 startup-class-key.pemmac5-library:startup roh21$ ls -ltotal 6-r--r--r--@ 1 roh21  108  1692 Jun 22 16:45 startup-class-key.pem

Still has read permissions to everyone. Just to demonstrate what happens I do this:

mac5-library:startup roh21$ chmod 600 startup-class-key.pemmac5-library:startup roh21$ ls -ltotal 6-rw-rw-rw-@ 1 roh21  108  1692 Jun 22 16:45 startup-class-key.pem

Is it impossible to change permissions to the user without root permission? I'd be grateful for any kind of help.