Answer by Pedro Romano for How to add IP restrictions to my amazon ec2 instance installed with ubuntu 12

Have you read this article: Tips for Securing Your EC2 Instance? I believe it has the information you need.

You should authorise your IP address (e.g. assuming your IP address is 1.2.3.4):

PROMPT> ec2-authorize default -p 22 -s 1.2.3.4

And then simply create SSH key pairs for all your users and authorise the public key of the pairs with the ec2-add-keypair command as described in the Ditch Those Passwords: Use ssh Keys of the above mentioned article. This way only the users with authorised SSH key pairs from the authorised IP will be able to connect.