Data masking is a technique that replaces sensitive information with realistic but fictitious values so the data stays usable for testing, development, or analytics without exposing the real thing. A masked record keeps the same format and behavior as the original while the actual private values are hidden.
The classic use case is non-production environments. Developers need data that looks and acts like production to build and test against, but handing them live customer records multiplies the places a breach can happen. Static masking permanently rewrites a copy of the dataset, while dynamic masking hides values on the fly as they are queried, based on who is asking. The mistake to avoid is masking that can be reversed or reidentified; if the technique is reversible or leaves enough real fields intact to re-link a person, it is not really protecting anyone. Well-designed masking preserves referential integrity so related tables still join correctly.
Why does data masking matter for the CISSP exam?
It falls under Domain 2, Asset Security. Candidates should distinguish masking from encryption and tokenization, understand static versus dynamic approaches, and connect it to protecting data in non-production use and to privacy requirements.