End-to-end encryption, explained with two phones

"End-to-end encrypted" is printed on so many products that it's easy to stop noticing. Here's what it means for iTell, explained with the two phones on your desk.

The two ends

In iTell, the "ends" are your Android phone and your iPhone. Nothing else: no server, no cloud, no relay. Encryption happens on one phone and decryption on the other. Anything in between, including the air around you, only ever sees scrambled bytes.

Step 1: Meeting in person

When you pair, the Android phone shows a QR code. It contains the phone's public key and a one-time token valid for five minutes. Your iPhone scans it, and the phones exchange long-term keys right there, in front of you.

Why does this matter? Because the hardest part of encryption is knowing *who* you're talking to. A QR code on a screen you can see is a very hard thing to fake from across the room.

Step 2: A fresh secret for every connection

Each time the phones connect, they each create new temporary keys and combine them with the long-term ones (the maths is called elliptic-curve Diffie-Hellman on the P-256 curve, followed by a key-derivation step, HKDF-SHA256).

The result is a session key that only these two phones know, and that's never sent anywhere. Even if one day a long-term key leaked, past sessions would stay locked, because their temporary keys are gone.

Step 3: Locked packets

Every message, every piece of voice, every contact is sealed with AES-256-GCM before it leaves the phone. Each packet carries a counter, so the other phone can tell if anything was changed, dropped or replayed.

So what can we see?

Our servers handle your account and license: your email, the number you typed when signing up, which two phones use your license, and your orders. That's it.

We never receive your calls, your texts, your contacts or your call history, because they never travel through us. We can't read them, lose them in a breach or hand them over, because we don't have them.

Keys that stay home

Your account keys are created inside the iPhone's Secure Enclave and the Android phone's hardware keystore. They can't be copied out of the phone, not by an app and not by us.

Read the full picture on our security page.