A hardware virtual machine is the de facto virtualization method for EC2, and it is the successor of paravirtualization (PV). The custom XEN hypervisor design efforts improve the performance of the virtual functions of HVM while cutting down multiple layers between the hypervisor and the operating system.
Linux instances are automatically provisioned with a public key in order to encrypt login information. They use the Secure Shell (SSH) V2 protocol under the public key infrastructure (PKI). This provides a mechanism in which a secret is broken down into two parts: the public key and the private key. The private key is available to the user, and is used in the SSH tunnel to authenticate and encrypt the communication channel for confidentiality between parties. The public key is installed in the ~/.ssh/authorized_keys in the filesystem of the instance...