File systems use Oracle-managed keys by default. Customer can encrypt data in their file system using their own Vault encryption key. The explanation is that File Storage Service encrypts all data at rest using AES-256 encryption algorithm. By default, File Storage Service uses Oracle-managed keys to encrypt and decrypt data. However, you can also use your own Vault encryption key to encrypt data in your file system. To do so, you need to create a key in Vault and associate it with your file system when you create or update it.