Three techniques
Only one of them is redaction.
The word is used loosely in this market. ***-**-6789 is masking — there is no key anywhere that restores it.
Hashing deserves a specific warning. An SSN has roughly a billion possibilities, so an unsalted hash of one is recoverable by brute force in seconds. A hash is not redaction for low-entropy identifiers. If a product stores hashed identifiers server-side, the salt handling is the whole question.
| Technique | Reversible? | What it is for |
|---|---|---|
| Masking / redaction | No — characters destroyed | Keeping the value out of every downstream system |
| Tokenisation | Yes, with the vault key | Preserving referential integrity; a payments pattern |
| Hashing | Not directly; brute-forceable at low entropy | Matching and deduplication |
Where it happens is the point
“We redact sensitive data” describes two very different systems.
Redact at rest, server-side. The raw value was transmitted, processed, and probably logged somewhere in the path before redaction occurred. The claim is about the final database row.
Redact at detection, on-device. The unredacted value never populates a serialisable structure at all.
Only the second means the value never left the machine. Ask which one, and ask where in the code path masking is applied.
What correct implementation requires
Five properties, and the first is where leaks live.
- 01
Mask before the record is constructed
Not before it is transmitted. The window between those two points is where leaks live.
- 02
Apply it to logs too, including debug builds
Most real PII leaks in security products are a debug print somebody forgot to remove, not an exfiltration feature.
- 03
Get the span right
A finding with the correct type and the wrong offsets means part of the real value survived into the record. Span accuracy is a redaction property, not a classification nicety.
- 04
Encrypt the local buffer anyway
Defence in depth: treat even redacted records as sensitive at rest.
- 05
Enforce it in CI
So the property is a build gate rather than a convention.
Related terms