If I'm understanding correctly your data source actually has both fields. The Encrypted Value, and the Unencrypted Value. I would be hesitant to try and do anything in a chart or master dimension like "If user rights are n show this field else show that field" because they could simply create their own table, or go to the Selections screen to see the unencrypted values.
It walks through the case where you simply need to hide certain columns (like unencrypted data) from certain users. But also walks through a case where the end user should see the unencrypted data for certain rows (like their own employees) but not for other rows (other teams employees.)