Pairing is how two phones learn each other's keys. Everything after that — every message, every photo — is sealed to those keys, and only those two phones can open it.
One phone shows, the other scans. The code carries a public key and a short-lived nonce; it does not carry anything secret, so it is safe to show in public. Each phone then sends the other its card, sealed.
When two phones pair without a camera — by Bluetooth or on the same Wi-Fi — each shows a six-digit confirmation code. Both phones compute it from the secret they just agreed and from both identities, in thirty-second windows. If the codes match, nobody sat in the middle. If they do not, stop: something is between you.
Every conversation has a safety number, shown on the contact's page. It is computed from both keys, in the same order on both phones, so it is identical on both ends. Compare it in person once and you have checked, for the life of the pairing, that nobody substituted a key. It changes only if a key changes — a reinstall, a new phone — and Channel tells you when it does.
If someone reaches you at a verified number or address, you see a request that says who they claim to be. Give them whatever name you like, or none — the name is for you. Accepting starts the pairing; it completes when both phones are next reachable, and you can leave the screen in the meantime.
English is the reference text; any translation is a convenience. Help is stored on this phone and never contacts anyone.