Chapter 3 · 1/5

Data minimisation

Why it matters not to give more than a task needs, and how that becomes possible.

5 min

You are walking into a concert. The person at the door has one question: "Is this person over 18?" Yet today, to answer it, you hand over your ID card. They see your name, date of birth, place of birth, document number, even your parents' names. The answer was a single "yes"; you gave away seven pieces of information.

This page explains why that matters and how digital credentials fix the imbalance. The idea is called .

Every transaction asks one question

Most moments when we show an ID are really looking for one answer. A hotel desk asks "Are you the person who booked?" A museum with a student discount asks "Are you a student?" An employer asks "Is this degree real, and is it yours?" A border post asks much more, and it has the right to.

The core of data minimisation is simple: the smaller the question, the smaller the answer should be. The concert door does not need your date of birth; it only needs to know that "over 18" is true.

With an ID card

Full name
Photo
Date of birth
Place of birth
Document number
Parents' names
Over 18

With a digital credential

Full name
Photo
Date of birth
Place of birth
Document number
Parents' names
Over 18

Left, what happens today: every field on the ID card is visible. Right, what should happen: only the answer to the question.

Why is extra data harmful?

Data you hand over does not disappear. It is photocopied, filed, typed into a computer or written into a register. Every stored piece of data carries three risks:

Leaks: databases get breached. Nobody can leak what they never held.
Reuse: data collected for one purpose drifts into marketing, profiling or sharing with others.
Identity theft: a document number, a date of birth and a mother's name together make it easier to act in someone else's name.

That is why laws such as in Türkiye and the in Europe require personal data to be processed for a stated purpose and in proportion. But the law alone is not enough: you cannot "cover up" one field of a plastic ID card. The rule exists; the tool does not.

How digital credentials make it easy

In a digital credential every piece of information is a separate field, and fields can be shown independently. The verifier sends a request: "Show me only the age information." The wallet shows the request to the person; if they agree, only that field leaves the phone. Because the credential still carries the issuer's signature, the verifier knows the single field it received is genuine.

Tamga Network also writes this principle into its rules. Every verifier that joins the network declares, when it registers, which data it will ask for and why. If a request goes beyond that registration, the wallet warns the person: "This organisation is asking for more than its registered purpose." The decision is still the person's, but now it is an informed one.

"Show only one field" sounds simple. But how do you hide part of a signed document and keep the signature valid? The next page explains the technique: selective disclosure.

Summary

Every transaction asks one question; answering it usually takes a single field.
Every extra piece of data is stored, can leak and can be reused for other purposes.
Digital credentials turn data minimisation from a rule into the easy, default behaviour.

Go deeper

Technical details and binding rules: