Proving your age without showing your date of birth
When a site only asks "over 18?", Tamga Wallet proves just that answer. Your date of birth, name and the credential itself are not shown.
By: Tamga Wallet team4 min read
You can prove you are over 18 without showing your date of birth. If a website only asks "are you over 18?", Tamga Wallet answers with a zero-knowledge proof: the website sees only that the answer is true; your date of birth, your name, your ID number and the credential itself are not shown. Android phones create this proof today. On iPhone the proving library is not finished yet, so there the wallet sends the "Over 18" field of your identity credential on its own, when the website accepts that; still only "yes" or "no" is sent.
Why is showing your date of birth more than needed?
A shop selling alcohol, an event entrance or a website with an age limit only needs to know whether you are above the limit. When you send a photo of your ID card, your date of birth, name, ID number and photo all go with it. Your date of birth alone already helps identify you; the more widely it spreads, the easier it becomes to combine it with other information (why oversharing has to stop).
What is more, once a photo of a document has been sent, it is no longer under your control: you cannot know where it is stored, who it is shared with or when it is deleted. A digital identity wallet turns this around: the other side receives only the answer it really needs, and you see what you showed to whom in History on your phone.
How does it work?
When you verify your identity once, remotely, in the app, an identity credential issued by the Tamga identity service arrives in your wallet. Besides your date of birth, it contains a separate "Over 18" field. A website asks for just that field. The wallet answers with a zero-knowledge proof; if your phone cannot create the proof (iPhone, for now), it sends that one field on its own, provided the website offers that option.
- On the website you choose age verification; the website shows a QR code. You scan it with Scan in the app.
- The approval screen opens. You see who is asking and the fields requested. Only "Over 18" should be listed.
- Tap Share and approve with your phone's lock (Face ID / Touch ID or the phone passcode).
- The website receives only the answer (the proof, or the yes/no field) and checks that it comes from an identity credential issued by the Tamga identity service.
Step by step: Prove your age.
What if the website asks for more?
You see every requested field on the approval screen; if it also wants your date of birth or your name, the list says so and the decision is yours. If a website asks for information outside its registered purpose, the wallet shows a separate warning and holds the "Share" button for a few seconds. You can try this with the "Age check" example in the "Show only what's needed" demo on the home page.
What if you are under 18?
If your credential does not meet the requested condition, nothing is shared; the app tells you in plain words that your credential does not meet the request's condition.
What do the two ways hide?
| With a zero-knowledge proof | If the phone cannot create the proof ("Over 18" field) | |
|---|---|---|
| Your date of birth | Not sent | Not sent |
| Your name, ID number | Not sent | Not sent |
| What does the website see? | Only the proof that you are over 18, and who issued the credential | The yes/no answer, the credential's signature and the identity service's name |
| Can two websites link you? | Two presentations cannot be linked | Each website gets a separate copy, which makes linking hard |
What is a zero-knowledge proof?
A zero-knowledge proof is a mathematical way of proving that a statement is true without showing the information behind it. The wallet proves "I am over 18" without showing the credential itself or its signature. The website learns only that the proof is valid and who issued the credential. The approval screen says that only a yes/no proof is sent and your document is not shown. Issuing institutions do not need to change anything for this. A longer explanation: Zero-knowledge proof: saying "I'm over 18" and nothing else.
Frequently asked questions
Do I need to verify my identity to prove my age?
Yes. The "Over 18" field is part of the identity credential, and the identity credential arrives after remote identity verification: Verify your identity.
Can the website find out my date of birth later?
Not from this presentation: the website receives only the fields you saw and approved on the approval screen. You can see what you showed to whom in History.
Does my identity credential replace a government ID?
No. The identity credential is issued by the Tamga identity service; it is not a government ID. Whether a website accepts it is that website's decision.
Read more
Related
- Article · ConceptsZero-knowledge proof: saying "I'm over 18" and nothing elseA zero-knowledge proof shows a statement is true without revealing the data behind it: what it proves, what it hides, how Tamga Wallet uses it.
- Article · ConceptsSelective disclosure: showing just one line of a documentSelective disclosure lets you show one field of a signed document, such as "is a student", while the rest stays hidden and the signature still checks out.
- Article · PrivacyLiving without oversharing: why 'show everything' must endPhotocopies and screenshots send a whole document when one answer is needed. Data minimisation under GDPR and KVKK, and how selective disclosure helps.
- GuideProve your ageIf a website asks only for “Over 18”, only that answer is sent: with a zero-knowledge proof your name, your date of birth and the credential itself are not shown.
- GuideWho I've shared withYou see every organisation you have shown information to, and what you shared when, in one list; from here you can ask for deletion or report.
Step-by-step help is in the Guide
Everything from setup to a lost phone, with the app’s own screens.
Get Tamga Wallet
On the App Store and Google Play. Carry your diploma, student card and tickets on your phone.
