Explain like I'm five · InfoSec

What is De-identification/Pseudonymization?

De-identification and pseudonymization, told as a story about swapping a guest's name tag for a number, with the real name locked in a separate vault.

GUEST LISTKim · 1990-03-02 · Seoul, OO-dongLee · 1985-07-09 · Busan, XX-donghand the list straight to a research team and even names show

The guest list has real names written out in full.Hand the list straight to a research team, and even the names show.

GUEST LIST (name removed)●●● · 1990-03-02 · Seoul, OO-dong●●● · 1985-07-09 · Busan, XX-dongonly one person in that dong was born that dayclues like birthdate and neighborhood reveal who it is — that's re-identification

Erasing just the name doesn't stop re-identification.Combine other clues — birthdate, neighborhood — and the guest can be identified again. That's re-identification.

GUEST LISTA017 · 1990-03-02 · SeoulA038 · 1985-07-09 · BusanA017A038the key-table vaultA017 = Kimpseudonymization = swap in a number tag; the real name goes in a separate vaultonly the vault's own key reconnects a number tag to its name

Pseudonymization swaps in a number tag and locks the real name in a separate vault.Only the vault's own key reconnects a number tag to its real name.

Swap in a number taga code instead of a name
The key table, in a vaultstored and locked separately
Turning a tag back into a name needs the key tablethe list alone can't link a tag to a name
Anonymization burns the key tableand strips other clues, so re-ID is impossible
ORIGINAL vs PSEUDONYMIZED vs ANONYMIZEDoriginal — real names, instantly identifiable, personal datapseudonymized — tag + vault key reconnects the name, still personal dataanonymized — key table burned, clues stripped, no re-identification, not personal datak-anonymity — group k similar guests so none stands out

Original, pseudonymized, and anonymized are not the same thing.Pseudonymized data is still personal data, since the vault key can reconnect it. Anonymized data has no key table and no clue left to identify anyone, so it isn't personal data.

A017A017other ledgerspurchase logslocation logscombined... narrows to one personthe more ledgers combined, the higher the re-identification risk

The more data combined, the higher the re-identification risk.So re-identification risk gets assessed up front. Ledgers from several castles are sometimes combined in a controlled place like the special reading room.

In one breath

Pseudonymization = swapping a name for a number tag and locking the key table away separately. Anonymization burns that key table and strips the remaining clues, so it's irreversible.

Pseudonymization processes data so an individual can't be identified without additional information; as long as that extra information exists, the data is still legally personal data. Anonymization makes the person unidentifiable even with other information, considering time, cost, and technology reasonably, so it is no longer personal data. Measures like k-anonymity and l-diversity are used to assess whether de-identification is adequate.

When grown-ups say it

Pseudonymization
Swapping in a number tag. Reversible with the key table (additional information). Still counted as personal data.
Anonymization
Burning the key table and stripping the clues. Re-identification isn't possible, considering time, cost, and technology reasonably. No longer personal data.
Additional information
The table linking number to name. The core of pseudonymization. The key table is kept apart from the list, encrypted and locked.
Re-identification
Finding the name again from other clues. A combination like birthdate and neighborhood can narrow it to one person.
k-anonymity
Grouping k people together. Groups at least k similar guests so no individual stands out.
Korea's Three Data Acts
The kingdom's rules for handling data. Korea's Personal Information Protection Act and related laws set the grounds and limits for handling pseudonymized data.
Data masking
Hiding only part of it. Similar to pseudonymization, but usually irreversible. → a number instead of a name
Privacy principles
The name tag belongs to the guest. Pseudonymization still operates under this principle. → the name tag belongs to the guest
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