How we find your friends without keeping your contacts

The first time you open aftrs, it's empty. You can't see anyone you know.

Most apps solve this by hoovering up your entire address book and storing it on their servers. That's the trade-off you learn to accept: hand over your contacts, or don't find your people. We didn't think that was good enough.

So we built a different way. You can let aftrs check for friends who are already here, without us ever storing a single contact number from your address book. Here's exactly how that works.

Follow one contact through the system

Say your friend Sam is in your address book. Here's exactly what happens to Sam's number.

1. It stays on your phone. When you let the aftrs app see your contacts, it reads the numbers and keeps them right there on your device. Those numbers stay on your own phone, no problem. aftrs handles the messy reality here: on an iPhone you might share only some contacts, change your mind later, or grant more over time. aftrs just works with whatever you've shared, whenever you share it.

2. It's turned into a fingerprint. The aftrs app turns Sam's number into a fingerprint right there on your device: a scrambled code that can't be turned back into the number. Only the fingerprint is sent to aftrs. That address book number itself is never stored or transmitted. The app only ever sends fingerprints it hasn't sent before, in small batches, so after the first time keeping things up to date is quick and light.

Think of it like a real fingerprint. You can check whether two match, but you can't rebuild the face from one.

3. It gets a private nametag. When aftrs receives Sam's number, it hands your app back a random ID, a meaningless string that just stands for "this contact" between your app and aftrs. Your app quietly remembers which number that ID belongs to. To anyone else, the ID means nothing at all.

Like a coat-check ticket. A number that means "your coat" only to you and the cloakroom, useless to anyone else.

4. aftrs looks for a match. Aftrs compares Sam's fingerprint against the fingerprints of everyone who's signed up. Each person's own number is fingerprinted when they log in. If two fingerprints match, it's the same number.

5. Your contacts get sorted. When your app asks "which of my contacts are here?", aftrs answers using those random IDs, never address book numbers. Your app turns each ID back into the right contact and shows you which friends are already on aftrs.

Like a one-way mirror. You can see who you already know. No one on the other side learns that you know them.

What this means for you

We never tell you who has you. We will never say that a specific person has you in their contacts. That's their private information, not ours to share. You only ever see people who are already in your contacts.

You control what you share. Grant some contacts today, more next week, or none at all. The system works the same. There is no penalty for being cautious.

Nothing to leak. Even if someone got hold of our database, there are no address book numbers in it, only one-way fingerprints. The privacy doesn't depend on us being

You can wipe it. Remove the app, and your address book data is gone from your device. There is no separate "delete my contacts from aftrs" step because aftrs never held them in the first place.

If you want a social app that finds your people without keeping your contacts, try aftrs.