Mesh Messenger — Every Phone Is a Relay

OSHI is a free, open-source, end-to-end encrypted messenger for iOS and Android that uses Bluetooth and Wi-Fi mesh networking to send messages without Internet or cellular service. OSHI is an alternative to Bridgefy, Briar, Meshtastic and bitchat for offline communication, and to Signal for private messaging.

A mesh messenger turns every phone running it into a relay. Instead of a star with a server in the middle, the network is whatever set of phones happen to be within radio range of each other, and a message finds its way across them hop by hop. This page describes how OSHI's mesh actually works, with the real numbers, and where a phone mesh stops and a radio mesh begins.

The three layers of OSHI's mesh

1. Discovery: Bluetooth Low Energy

With OSHI open, your phone advertises a short identifier and scans for other OSHI phones. BLE is built for exactly this: it can advertise and scan for hours on a small fraction of the battery. Range is roughly 100 m with a clear line of sight and 10–30 m through walls and bodies. On iOS OSHI uses Apple's Multipeer Connectivity; on Android, BLE plus Wi-Fi Direct.

2. Transport: BLE for text, Wi-Fi Direct for everything else

Short encrypted text packets go over the BLE link directly. A photo, voice note or file would take minutes over BLE, so OSHI negotiates a Wi-Fi Direct link between the two phones for the transfer and drops it afterwards. No access point or hotspot is involved.

3. Routing: multi-hop, store-and-forward

Every packet carries a hop counter. If the recipient is not directly reachable, any OSHI phone that receives the packet stores it and forwards it to any new OSHI phone it meets, until the counter reaches five or the packet is delivered. Because the packet was encrypted for the recipient before it left the sender (X3DH + Double Ratchet, AES-256-GCM), a relay carries ciphertext it cannot open, and a seized relay phone reveals nothing about the conversation.

What "up to five hops" means in real space

Hop range compounds only where there are relays. Five phones spaced 80 m apart in a park can carry a message 400 m. Five phones in one apartment carry it 400 m of nothing. In a crowd of thousands the practical limit is not hops but time: each store-and-forward step waits for a new phone to come into range, so delivery across a festival field takes seconds to minutes, not milliseconds. A mesh is a probability, not a wire.

Phone mesh vs radio mesh

OSHI sits on the phone side, with an optional LoRa node that bridges the phone mesh to kilometre-scale links. Note that messages bridged over the LoRa link are not encrypted by that link, as our App Store listing states.

What the mesh cannot do

• Reach anyone beyond the chain of phones. When no OSHI phone is in range, the message waits.
• Relay from a phone that is locked in a pocket for hours. iOS in particular limits background Bluetooth; keep OSHI open on the phones that should relay.
• Carry voice or video calls over Bluetooth alone. Calls are end-to-end encrypted but need an IP path.
• Talk to other apps' meshes. OSHI, bitchat, Bridgefy and Briar each use their own protocol.

Other mesh messengers

bitchat relays up to seven hops over BLE only, with public-domain code. Bridgefy relays over BLE with a closed-source app. Briar syncs directly with contacts over Bluetooth, Wi-Fi and Tor. Meshtastic meshes LoRa radios. The best offline messenger page compares them in one table, and the mesh networking guide covers the theory.

Frequently asked questions