How anynear works in detail.

Every installation creates two random key pairs: one for signing (Ed25519) and one for key exchange (X25519). The private parts leave the device only in your own backup or when you pair another device of your own.

If you use several devices, a key chain sits above them: a root key certifies a person key, which signs the list of your own devices (16 at most). Your contacts remember the root key. A removed device is listed as revoked and stays revoked.

If a device is lost, the root key issues a new person key, the mailbox moves, and each of your circles changes its key.

A circle is a random 32-byte secret. It sits in the invitation link after the # sign. A browser never sends that part to a server, not even to our website.

From the secret the app derives separate keys: one for messages, one for the circle’s storage, one for its place at the locations and one for the envelope that hides the packet header from the locations.

When someone is removed from a circle or leaves it, the circle gets a new secret. It is sent to each remaining device individually encrypted. A removed member keeps what they already had but sees nothing new.

Direct messages are encrypted separately for each of the recipient’s devices, with the key of that pair of devices. They are kept in the recipient’s personal mailbox. Only their own devices may read and list it; contacts only get the right to write into it, and that right expires and can be revoked.

Every packet sent over the internet carries the signature of the sending device. It sits inside the encryption, so the locations do not see it. The app drops anything that does not match the sender’s known key chain.

The locations are stores for encrypted packets. They check signatures and permissions; they read nothing.

• Not visible: texts, pictures, files, passwords, names, circle names, who writes to whom in terms of persons, phone numbers (there are none).
• Visible: the identifier of the place written to (a public key, not a name), the size and time of each packet and its expiry.
• Visible for direct messages: the public key of the writing device. A location can therefore see that a certain device writes into a certain mailbox, without knowing who either belongs to.
• Visible as with any server: the IP address of the connection while it lasts.

There are currently 5 locations in 4 countries, run by different providers. Every packet has a name derived from its content (SHA-256), cannot be changed and is kept at three locations run by different providers. Each device works out which three from the list of locations.

The locations sync with each other every minute. If one does not answer for ten minutes, another one receives its copies; once it is back, it takes over again. There is no majority vote: even a split network keeps accepting on both sides and catches up afterwards.

The list of locations is signed with a fixed key. The app only accepts lists whose signature is valid and only talks to locations from that list. A link or a foreign server cannot redirect it to other locations.

A message counts as sent as soon as one location holds it. If none can be reached, it waits on the device for up to seven days.

Over radio, anynear uses radios running the free Meshtastic software (LoRa). All anynear radios share one radio channel. Its key is public and protects nothing. What is protected is the content: it is encrypted exactly as over the internet, with the key of the circle or of the pair of devices.

A radio packet is 233 bytes at most. Depending on the kind, 83 to 152 bytes remain for text; photos and files never go by radio. Instead of fixed identifiers, the packet carries identifiers that change every hour, so that listeners cannot track sender and destination over time.

If a device within range has internet access, it passes packets it hears into the network unchanged, and the other way round. It cannot read them in the process.

Your own storage hangs on a random secret that only your devices know. It cannot be derived from any public key; from outside it is not even visible that you have a storage. Every file gets its own random key. Name, type and size sit in an encrypted entry.

Passwords are encrypted twice: once with a key of the app that your phone keeps behind its screen lock (fingerprint, face or PIN), and once more for keeping them at the locations.

Deleted files stay in the bin for seven days and are then removed from the locations.

The backup is a file you create and keep yourself. It contains your keys, your history and your attachments. From your password (at least 8 characters) and a random value, PBKDF2-HMAC-SHA256 computes the key in 600,000 iterations; encryption is AES-256-GCM.

We never receive the file and do not know the password. If you forget it, nobody can open the backup.

Android: no push service. The app keeps a connection to the locations itself.

iPhone: a location asks Apple to wake the device. This wake-up contains no message content and no sender. The app then fetches the message itself and decrypts it on the device. Apple learns that and when a device was woken.

In the browser, wake-ups go through the push service of the browser vendor, likewise without content.