Implement column-level security

  • 8 minutes

Column-level security (CLS) allows you to restrict column access in order to protect sensitive data. It provides granular control over who can access specific pieces of data, enhancing the overall security of your data warehouse.

Secure sensitive data

Let's consider a practical example of column-level security (CLS) in the healthcare industry. Suppose we have a table named Patients with the following columns: PatientID, Name, Address, DateOfBirth, and MedicalHistory.

The MedicalHistory column contains sensitive health information about the patients. As per the healthcare regulations and privacy laws, this information should only be accessible to authorized medical personnel such as doctors or nurses.

Here's how you might implement column-level security in this scenario:

  1. Identify the sensitive columns: In this case, the MedicalHistory column is identified as containing sensitive data.

  2. Define access roles: Define roles such as Doctor and Nurse who are allowed to access the MedicalHistory column. Other roles such as Receptionist or Patient might be restricted from accessing this column.

  3. Assign roles to users: Assign the appropriate roles to each user in the warehouse. For example, user DrSmith might be assigned the Doctor role, while user JohnDoe might be assigned the Patient role.

  4. Implement access control: Restrict access to the MedicalHistory column based on the user's role.

Column-level security can help ensure that sensitive health information is only accessible to those who are authorized to see it, though protecting patient privacy and complying with healthcare regulations.

Configure column-level security

In the scenario we've recently explored, the syntax to use for implementing column-level security might look as follows:

-- Create roles
CREATE ROLE Doctor AUTHORIZATION dbo;
CREATE ROLE Nurse AUTHORIZATION dbo;
CREATE ROLE Receptionist AUTHORIZATION dbo;
CREATE ROLE Patient AUTHORIZATION dbo;
GO

-- Grant SELECT on all columns to all roles
GRANT SELECT ON dbo.Patients TO Doctor;
GRANT SELECT ON dbo.Patients TO Nurse;
GRANT SELECT ON dbo.Patients TO Receptionist;
GRANT SELECT ON dbo.Patients TO Patient;
GO

-- Deny SELECT on the MedicalHistory column to the Receptionist and Patient roles
DENY SELECT ON dbo.Patients (MedicalHistory) TO Receptionist;
DENY SELECT ON dbo.Patients (MedicalHistory) TO Patient;
GO

In this example, we first create the roles Doctor, Nurse, Receptionist, and Patient. We then grant SELECT permissions on all columns in the Patients table to all roles. Finally, we deny SELECT permissions on the MedicalHistory column to the Receptionist and Patient roles. This ensures that only users with the Doctor or Nurse role can access the MedicalHistory column.

Understand the benefits

In the realm of warehouse security, two commonly used techniques are column-level security and views. Both methods serve to restrict access to sensitive data, but they do so in different ways and offer different advantages. The following table provides a comparative analysis of these two techniques across various aspects such as granularity of access control, maintenance, performance, transparency, and flexibility.

This comparison can help you understand the strengths and weaknesses of each method and guide you in choosing the most suitable approach for your specific application requirements.

Aspect Column-Level Security Views
Granularity of Access Control Allows control at a more granular level. Can specify different access rights for different users or roles on different columns within the same table. Would need to create different views for different sets of permissions.
Maintenance Permissions are tied to the columns themselves, so they automatically adapt to changes in table structure. If the underlying table structure changes, views may need to be updated to reflect these changes.
Performance Generally more efficient because it operates directly on the table data. Can introduce performance overhead, especially if they are complex or if the underlying tables are large.
Transparency The restrictions are transparent to the user. The user queries the table as usual, and the database engine takes care of applying the security rules. The user needs to query a different object (the view instead of the table).
Flexibility Less flexible than views. Very flexible and can provide row-level security (by including a WHERE clause in the view definition) in addition to column-level security. They can also transform the data (for example, by calculating derived columns) which is not possible with column-level security.

The choice between using column-level security or views will depend on the specific requirements of your application. Always make sure to test any security changes in a safe environment before applying them to a production warehouse.