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Dynamic Data Masking (DDM) is a powerful feature in Azure SQL Database that helps protect sensitive data from unauthorized access by masking it in query results. This is especially useful for preventing non-privileged users from viewing confidential information while still allowing them to perform essential database operations.

What is Dynamic Data Masking?

Dynamic Data Masking automatically obfuscates data in the result set of a query. For instance, if you have a column with credit card numbers, you can mask the data so that users only see a portion of the number, while the rest is replaced with a masking character like X.

Implementing Dynamic Data Masking

Let’s walk through an example using the Sales.CreditCard table from the AdventureWorks database on an Azure Managed SQL Instance.

  1. Identify the Columns to Mask

    Start by identifying which columns contain sensitive data. In this case, let’s say we want to mask the CardNumber column.

  2. Apply a Masking Rule

    You can add a masking rule to the CardNumber column with a simple SQL command:

    ALTER TABLE Sales.CreditCard
ALTER COLUMN CardNumber ADD MASKED WITH (FUNCTION = 'partial(0,"XXXX-XXXX-XXXX-",4)');

    This masks the middle digits of the credit card number, displaying only the last four digits.

  3. Test the Masking

    Now, when a user without the appropriate privileges queries the CardNumber column, they’ll see something like this:

    SELECT CardNumber FROM Sales.CreditCard;

    Result:

    XXXX-XXXX-XXXX-1234

    The actual card number is masked, but authorized users can still perform queries without seeing the full number.

  4. Managing Masking Permissions

By default, database administrators and other highly privileged roles can see unmasked data. To prevent a user from viewing unmasked data, you need to ensure they don’t have the UNMASK permission:

   REVOKE UNMASK ON DATABASE::AdventureWorks2019 FROM [User];

Dynamic Data Masking is a straightforward and effective way to protect sensitive information in your Azure Managed SQL Instances. It’s easy to implement and can help you meet compliance requirements by ensuring that non-privileged users can’t see confidential data. Give it a try to enhance the security of your databases!

Peace ✌️