How Chime actually works.

How it actually works

Chime is a peer-to-peer messenger with no central server holding your data. When you send a message, delivery is attempted along a priority of transports, most direct first, and the first one already connected wins:

1. Local network (WiFi/LAN): devices announce themselves over mDNS (_chime._tcp) and open a direct TCP connection that never leaves the subnet.
2. Direct over the internet (WebRTC): a NAT-traversed data channel straight to the recipient's device, using STUN only. There is deliberately no TURN server; pairs that can't hole-punch fall through to the next path.
3. DHT stream (Hyperswarm): a hole-punched, Noise-encrypted stream established through a public distributed hash table. No Chime server involved at all.
4. Everything at once: if no live direct path exists, Chime fires the remaining transports in parallel: the relay, the Bluetooth mesh (BLE), and Tor if you've turned Tor Mode on. Whichever lands first wins; the receiving device drops duplicates.

Peers find each other through DHT rendezvous topics derived from cryptographic material: a private per-pair topic only the two contacts can compute, a per-recipient inbox topic for offline delivery, and a Chime-ID topic with signed introductions so adding a contact by ID works with no server at all. On a local network, discovery is plain mDNS. The relay offers a lookup too; it is one path among several, not the spine.

When a recipient is offline, delivery is store-and-forward over the DHT: your guardians act as custodians, holding a sealed blob at the recipient's inbox topic (up to 32 KB per blob, 200 blobs, 7-day expiry) until they reappear. The Bluetooth mesh does live multi-hop forwarding between nearby devices when there is no internet; WiFi Direct and hotspot transports are there as opt-in extras for fully infrastructure-free links.

The cryptography, named

End-to-end encryption is built on the NaCl family. Your identity is an Ed25519 keypair generated on first launch and kept in the device's hardware-backed secure store, encrypted at rest under a PIN-derived key. It never leaves the phone.

One key to rule them: the X-Wing keypair and the Tor onion address are deterministically derived from the identity secret, so a guardian recovery or device transfer restores all of them at once.

The security model

On-device controls for the paranoid, and rightly so:

That quiet notification, explained

While Chime is connected in the background, Android shows one small notification in the shade, filed under Muted: "Messages arrive instantly; nearby contacts can reach you." It never buzzes, never makes a sound, carries no badge, and never contains a message, a name, or anything private; it is the same fixed line for everyone, and tapping it just opens Chime. It is not a bug and it is not surveillance. It is the price of doing push notifications without Google, and we want you to know exactly why it is there.

Almost every other messenger delivers background messages through Google's push service (FCM): the message wakes your phone by travelling through Google's servers. The content can be encrypted, but the delivery itself tells Google which device received a message and when, and patterns of delivery are patterns of communication. Chime refuses that trade.

The only other way Android lets an app stay alive to receive messages is a foreground service, and Android's contract for a foreground service is blunt: the app must show a persistent notification so you always know it is running. That visibility is arguably a privacy feature; nothing runs behind your back. The service itself is light. It does not wake the screen or poll the network; it simply stops Android from killing the connection Chime already holds.

One honest limit: in Android's deepest battery-saving state (Doze), even a foreground service gets paused, so delivery can wait until you next wake the phone. That is the cost of refusing Google's push pipeline, and we accept it.

Recovery, in detail

Recovery uses Shamir secret sharing. Your identity and contacts are encrypted under your Vault Word and Vault Code, then the backup is split into opaque shares, one per guardian you choose. The threshold scales with your guardian count: with one or two guardians, all shares are needed; with three or more, a strict majority reconstructs it (three of five, four of six). No guardian alone can do anything.

There is deliberately no seed phrase to photograph and no cloud backup for anyone to demand. If you're just moving to a new phone, an in-person device transfer over Bluetooth carries everything across directly.

What Chime does not protect against

No tool protects everything. Being straight about the limits is how we earn the rest of your trust.

Verify your download

Every release APK is signed with the same key and its checksum is published here. Confirm the file you downloaded matches before installing.

The checksum above is for the current beta and changes with each release; this page is updated alongside the download. If a value does not match, do not install, and tell us at support@chime.tw.

Source & design docs

Chime is licensed under the GPL-3.0: React Native with a small amount of native Kotlin for the transports. The full source is public.

Codeberg was a deliberate choice, not a default. It is run by a non-profit association, funded by its community, and built entirely on open-source software, with no ads, no trackers, and no corporate owner mining what happens there. A messenger whose whole point is nobody in the middle should not keep its source with a data-hungry giant; it is the same reasoning that keeps Google's push service out of the app.

Two honest notes. Release downloads on Codeberg link back to this site, because the APK is larger than Codeberg's release limit, and the canonical, checksummed download lives here anyway. And the design docs in the repository's docs/ folder are still being tidied for publication; they are a work in progress and will appear here soon.

The site itself

This site makes no third-party requests: no fonts, scripts, images, analytics, or embeds from any other domain. Static HTML, readable without JavaScript. The same server quietly doubles as the relay: sealed envelopes over WebSocket, nothing stored.

Don't take our word for it. Open your browser's Network tab and reload; you should see requests to this domain only.