Cravage

Cravage lets a group of people in the same room find their average without anyone revealing their own figure. Daily steps, hours of doomscrolling, what a car or a business is worth, how your numbers benchmark against a peer group: anything you would rather not say out loud, or not say first. HOW IT WORKS One person opens a room and says what is being averaged. Everyone else joins from their own iPhone. Each phone shows the same short room code, and everyone confirms it matches before anything is sent. Then each person types their figure, and the average appears on every phone at once. WHAT MAKES IT PRIVATE Cravage uses secure aggregation, so nobody has to be trusted with the figures: not a colleague, not a survey company, not a server holding a decryption key. Your private figure is processed on your phone; the app sends a masked share to the other participants. Every pair of phones agrees a secret random number, and each person sends only their figure plus those secrets. When all the masked numbers are added together, the secrets cancel out and only the true total remains. Every phone does that addition itself and checks a digital signature on every masked number. The person who opened the room passes the messages along but cannot read anyone's figure on their own, as long as everyone checks the room code and counts the phones in the room; they can still stop a round, or add participants that exist only on their own phone, and counting is what catches that. NO SERVER, NO ACCOUNT Cravage is peer-to-peer: phones talk directly to each other over Wi-Fi. Cravage has no server, no sign-up, no analytics and no adverts. It saves your nickname and your light or dark setting on your phone. Round results are not stored, unless you choose to share a transcript. CHECK IT YOURSELF Any round that every phone agreed on can be shared as a transcript that shows the masked numbers, the signatures and the result. The same open-source verifier that checks the web version checks the phone's transcript, on any computer. PRICING Groups of exactly three are free, always. A one-off purchase lets the person opening the room run groups of four to eight. Only that person pays; joining is always free. There is no subscription. GOOD TO KNOW Everyone needs an iPhone with Cravage installed, within Wi-Fi range of each other. The maths hides figures up to a trillion in any unit. If everyone else in a group conspires, they can work out the remaining person's figure; that is inherent to the technique, and the app says so where you enter your sensitive figure. Three is the minimum, and the smallest group where no one else can work out your figure alone; in a group of three, the other two together can. Cravage is open source. The code, the plan and independent AI reviews of its design are published at github.com/dylanil/cravage-ios.