Introducing Crowdbook: shared contacts without the surveillance
Why we built a crowd-sourced address book that keeps your group current while the server never sees a thing it can read.
Everyone knows the problem. Someone in the group gets a new phone number, posts it to the chat, and half the group never updates it. Months later you’re texting a stranger who inherited the old number. Multiply that across a whole soccer team, an extended family, or a neighborhood association, and keeping contacts current becomes a chore nobody signs up for.
The usual fixes all have the same flaw: they ask you to hand your address book to someone who can read it. A shared spreadsheet, a contacts-syncing app, a group in some social platform — in every case, a company sits in the middle with full view of who you know and how to reach them.
Crowdbook takes a different path. It lets a group pool contact details and keep them automatically in sync, while the server that runs it is structurally incapable of reading those details. Every attribute is encrypted on your device before it’s uploaded. What the server stores is ciphertext it holds no keys for.
What that means in practice
- You join a group — your family, your team, your club.
- You choose exactly which of your details to share into it.
- Your device encrypts them and uploads only the ciphertext.
- Everyone else’s devices pull the update, decrypt it locally, and merge it into their phone’s own Contacts app.
No group-chat announcements. No spreadsheet. No company reading your rolodex.
This is just the start
We’re building the iOS and Android apps now, and we’ll be writing here about the decisions behind them — the cryptography, the sync engine, and the tradeoffs of doing privacy properly on a phone. If that’s your kind of thing, the zero-knowledge deep-dive is a good next read.
Want to follow along or try it when it’s ready? Get in touch.