Block Volume Encryption
By default all volumes and their backups are encrypted using the Oracle-provided encryption keys. Each time a volume is cloned or restored from a backup the volume is assigned a new unique encryption key.
You have the option to encrypt all of your volumes and their backups using the keys that you own and manage using the Vault service.If you do not configure a volume to use the Vault service or you later unassign a key from the volume, the Block Volume service uses the Oracle-provided encryption key instead.

This applies to both encryption at-rest and in-transit encryption.
Object Storage Encryption
Object Storage employs 256-bit Advanced Encryption Standard (AES-256) to encrypt object data on the server. Each object is encrypted with its own data encryption key. Data encryption keys are always encrypted with a master encryption key that is assigned to the bucket. Encryption is enabled by default and cannot be turned off. By default, Oracle manages the master encryption key. However, you can optionally configure a bucket so that it's assigned an Oracle Cloud Infrastructure Vault master encryption key that you control and rotate on your own schedule.
Encryption: Buckets are encrypted with keys managed by Oracle by default, but you can optionally encrypt the data in this bucket using your own Vault encryption key. To use Vault for your encryption needs, select Encrypt Using Customer-Managed Keys. Then, select the Vault Compartment and Vault that contain the master encryption key you want to use. Also select the Master Encryption Key Compartment and Master Encryption Key.