How many layers of encryption are commonly available to a database?

Databases typically utilize one layer of encryption, often referred to as "data-at-rest encryption." This encryption secures the data stored within the database files, protecting it from unauthorized access when the database is not actively being accessed or during data backup processes.

While some database systems may implement additional security measures such as access control, activity monitoring, or even transport encryption when data is in transit (like SSL/TLS), these do not necessarily count as additional layers of encryption of the data stored within the database itself. Thus, the primary focus remains on that single crucial layer responsible for safeguarding the data at rest, making one layer the commonly recognized standard in many implementations.

In considering the other options, they imply a higher number of encryption layers than what most database technologies standardize around, which may lead to unnecessary complexity without providing proportional security benefits for the typical use cases.