Database Encryption

structured database stores data in tables
table data is stored as files on a volume
- access is mediated through a database management system (DBMS) running a database language such as SQL
database is hosted on a server and accessed by client applications
underlying files could be protected by a disk or volume encryption product running on the server
- has an adverse impact on performance
  - so commonly implemented by the DBMS or by a plug-in
encryption can be applied at different levels
- options depend on DBMS
- the following are based on Microsoft SQL Server DBMS

Database-Level Encryption

aka page-level encryption
occurs when any data is transferred between the disk and memory
- referred to as transparent data encryption (TDE) in SQL server
page is the means by which the database engine returns data request by a query from the underlying storage files
this encryption means all records are encrypted while they are stored on disk
- protects against theft of underlying media
- encrypts logs generated by database

many databases contain secrets that should not be known by the db admin
- public key encryption solves this
  - by storing the private key used to unlock the value of a cell outside the database
cell/column encryption is applied to one or more fields within a table
- less of a performance impact than database-level encryption
- can complicate client access to data
- works in many ways
  - with SQL Server’s Always Encrypted feature
    - data remains encrypted when loaded into memory
    - only decrypted when client app supplies the key
    - plaintext key not available to DBMS
      - admin cannot decrypt the key
    - allows for separation of duties between db admin and data owner
      - important for privacy
some solutions support record-level encryption
- e.g., healthcare data
  - each customer data is record-level
  - encrypted with its own key
  - allows for compliance requirements