Permissions 0664 for '/home/centos/Crystal-LTN.pem' 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: it is required that your private key files are not accessible by others

$ sudo chmod 600 /path/to/my/key.pem

Example 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.