Protecting SQL Server Data : Obfuscation Methods (part 3) - Numeric Variance,Nulling

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Numeric Variance

Numeric variance is a process in which the numeric values that are stored within a development database can be changed, within a defined range, so as not to reflect their actual values within the production database. By defining a percentage of variance, say within 10% of the original value, the values remain realistic for development and testing purposes. The inclusion of a randomizer to the percentage that is applied to each row will prevent the disclosure of the actual value, through identification of its pattern.

In the HomeLending database, we will create a user defined function called Numeric_Variance that increases or decreases the value of the value passed to it by some defined percent of variance, also passed as a parameter to the function. For example, if we want the value to change within 10% of its current value we would pass the value of 10 in the @ValPercent argument.

A randomizer is added through the use of the vwRandom view. This will vary the percent variance on a per execution basis. For example, the first execution may change the original value by 2%, while the second execution may change it by 6%.

The script to create this Numeric_Variance function, which can be referenced as needed in other views and stored procedures, is shown in Listing 6.

Listing 6. The Numeric_Variance UDF.

To employ this method of masking in a development database, simply use an UPDATE statement to change the column's value to a new value, using our Numeric_Variance function, as shown in Listing 7.

Listing 7. Updating a development database to use numeric variance.


The process of nulling is the replacement of sensitive data with a NULL value, thus rendering the sensitive data unavailable in the development database. While this certainly protects the sensitive data, since the values are no longer known in the database, it does present issues if there are dependencies upon this data or constraints that do not permit a NULL value. Also, use of nulling can also present difficulties when trying to troubleshoot issues that specifically involve sensitive data.

To employ this method of masking in a development database, simply use an UPDATE statement to set the column's value to NULL, as shown in Listing 8.

Listing 8. Nulling a database column.

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