What security object is required to enable transparent data encryption?

To enable transparent data encryption (TDE) in Azure SQL Database or SQL Server, the master key is crucial. The master key serves as the root of the encryption hierarchy for database encryption. It is used to protect the encryption keys that encrypt the data and can be stored either in the database itself or in an external secure location, depending on the configuration.

When TDE is enabled, the database engine creates a database encryption key that is encrypted by the master key. This allows for seamless encryption of data at rest without any changes needed in the application layer, as TDE works transparently to the application using the database.

The other options listed do not serve the same function in the context of TDE. Column encryption keys are used in cell-level encryption, file encryption keys pertain to encrypting files in storage rather than databases, and user-defined roles are related to permissions. Therefore, the master key is a fundamental component required for establishing transparent data encryption in Azure SQL databases, making it the correct answer.