Permissions 0664 for '/home/centos/.ssh/Keystothecstle.ppk' are too open. It is required that your private key files are NOT accessible by others. This private key will be ignored. code example
Example 1: Permissions 0664 for '/home/kapua/keys/dev11' are too open.
chmod 600 ~/.ssh/id_rsaExample 2: It is required that your private key files are NOT accessible by others ubuntu
chmod 400 {keyfile}.pem is what amazon instructed and it works.