What can the key pair be used for?

A key pair is required to create a DBaaS instance.
What can the key pair be used for?

A.
They key pair is used to start up, shut down, and manage EM Expressavailability.

B.
The keys are used to control the encryption that is used by DBaaS database instances:
the first is for network encryption and the second is for database encryption.

C.
The keys replace password use. DBaaS instance use only key pairs;password
authentication is not enable for SSH default connections.

D.
Communication between instances in a DBaaS account is controlled by network access
rules and network groups.

Explanation:
Before you create a Database Cloud Service instance you can chooseto create a Secure
Shell (SSH) public/private key pair. The SSH keys are used to facilitate secure access to
the compute nodes that support your database deployments.
Using Oracle Database Cloud Service (February 2017), 1-7
https://docs.oracle.com/en/cloud/paas/database-dbaas-cloud/csdbi/using-oracle-databasecloud-service.pdf