National ID numbers in documents: the rules country by country

A national ID number in a document follows more than the GDPR. Article 87 GDPR lets each EU country set its own conditions, and several have strict rules. The safe default: keep the number only where a law requires or allows it, and mask the whole number everywhere else.

This guide covers eight countries as of October 2026. It is general information, not legal advice. For a real case, ask your data protection officer (DPO) or a lawyer.

What does Article 87 GDPR say?

Article 87 has two sentences. First, member states “may further determine the specific conditions” for processing a national identification number. Second, where they do, the number may be used “only under appropriate safeguards” for the person’s rights and freedoms.

In plain words, the GDPR sets the floor and each country adds its own conditions. The article also covers “any other identifier of general application”, meaning a number that many services use.

What are the rules in each country?

Spain: which digits may be shown?

Spain has a precise rule on partial display. Additional provision 7 of the LOPDGDD, Spain’s 2018 data protection law, applies when a public administration publishes an act. The act names the person plus four random digits of the ID number, never the name with the full number.

In March 2019, Spain’s data protection authority (AEPD) and three regional authorities published a provisional criterion. For a DNI written 12345678X, show the fourth to seventh digits: ***4567**. For an NIE written L1234567X, show ****4567*.

Why are national numbers so risky in a leaked document?

First, they last. Germany’s tax ID is a uniform, permanent identifier under § 139a AO. The Austrian SVNR usually stays the same for life, says a 2008 parliamentary answer. Second, they link files, as the Dutch data protection authority (AP) warns about the BSN. Third, many hide personal details in their digits.

• France: the NIR shows sex, year and month of birth, and place of birth.
• Belgium: the birth date, then a sequence number that is even for women and odd for men.
• Germany: the social insurance number holds the birth date, the birth name’s initial and a serial that may show sex.
• Austria and Luxembourg: the SVNR usually ends with the birth date, the Luxembourg number starts with it.
• The German tax ID is different: by law, it may not be derived from other data about the person.

So masking the name protects little if the number stays. A Belgian number next to a job title reveals age and sex at a glance.

Where do national numbers hide in a document?

• Headers and footers, repeated on every page of a payroll or insurance template.
• Payslip boxes and the filled fields of a PDF form.
• Scanned ID cards: Luxembourg’s 2013 law puts the number on the identity card.
• Barcodes and QR codes, which can encode the number. You cannot read them, but a phone can.
• File names and email subjects, which leak the number before anyone opens the file.

ID copies have their own rules. In Germany, § 20 PAuswG allows a copy only by the holder or with the holder’s consent. The copy must be clearly marked as a copy, and people other than the holder may not pass it on to third parties. The Dutch AP tells people to make the BSN unreadable on a copy if the organisation may not use it.

Take Erika Mustermann’s payslip, sent to an outside auditor. Her tax ID sits in the header and her social insurance number in a box. The auditor checks totals, not identities. So both numbers go, everywhere they appear.

ONYRI Sanitize looks for these numbers country by country. It verifies the check key of the Belgian national number, the German tax ID and social insurance number, and the Austrian SVNR. The Dutch BSN needs its label or a valid check. It spots the NIR, DNI, NIE, codice fiscale and Luxembourg number by format. Limit: a number that fails its check, for example after a misread scan, can stay visible. Read the “Detected data” list.

How do you mask a national number properly?

1. Check whether a law requires or allows the number for this recipient, like the tax office. If not, it goes.
2. Mask the whole number, unless a rule like Spain’s sets the visible digits.
3. Find every occurrence: headers, footers, form fields, appendices and scans.
4. Draw a box over barcodes, QR codes and ID card photos.
5. Export a flattened file, then try to copy the masked text. Nothing should come out.
6. Rename the file if its name reveals the number or the person. Keep the original safe.

Frequently asked questions

Sources & references