OSHI

Send a message with no internet, no SIM card, and no account.
Phones relay for each other over Bluetooth. Everything is end-to-end encrypted.

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The one thing OSHI does that others don't

Turn on airplane mode. Open OSHI. Your messages still send.

Nearby phones running OSHI form a Bluetooth mesh and pass encrypted packets for each other, hop by hop, until one of them reaches the recipient — or reaches the internet. No cell tower, no Wi-Fi, no server in between.

That matters in three situations, and they are not hypothetical:

• A protest or a stadium where the cell network is saturated or shut off.
• A plane, a boat, a basement, a mountain — anywhere with no coverage.
• A country that cuts the internet. OSHI needs no VPN to keep working locally.

Everything else — the encryption, the absence of a phone number, the disappearing messages — exists in other apps too. This one does not.

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How the encryption works

OSHI implements the Double Ratchet with X3DH key agreement — the same construction Signal uses — with AES-256-GCM for message encryption and Curve25519 for key exchange. Forward secrecy and post-compromise security both hold: an attacker who steals today's keys can read neither yesterday's messages nor tomorrow's.

Your identity is a keypair generated on your device. There is no phone number, no email, no account, and nothing to seize. You add someone by scanning a QR code or pasting their public key.

The implementation is in this repository and you can read it:

File	What it is
src/DoubleRatchet.swift	The ratchet: chain keys, skipped-message keys, DH steps
src/OSHICryptoV2.swift	X3DH, AEAD, the header format
src/MeshNetworkManager.swift	Peer discovery, routing, store-and-forward
src/CrossPlatformMesh.swift	The iOS ↔ Android bridge: BLE presence, Bonjour discovery, TCP transport
src/MeshRelay.swift	Multi-hop relay: hop ceiling, loop suppression, dedup cache
docs/protocol.md	The wire protocol, in full
docs/encryption.md	Threat model and key lifecycle

On "open source", precisely: the cryptographic core, the mesh layer and the bot SDK are published here under MIT. The application shell around them — UI, App Store plumbing, media pipeline — is not. We would rather tell you exactly what you can audit than claim a green checkmark we have not earned. If you find a flaw in what is published, see the bug bounty below.

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Also in the app

Steganography. Hide a message inside an ordinary photo. The carrier image looks and opens like any other picture.

Covert channels. Traffic that resembles ordinary HTTPS requests, for networks that block or fingerprint messengers.

Offline AI. A local model runs on the device. Nothing is sent anywhere.

Encrypted voice and video calls, peer-to-peer where the network allows it, relayed through a blind TURN server where it does not.

Bot API with a Python SDK — build a bot that talks to a group without ever touching a phone number.

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How OSHI compares

	OSHI	Signal	Session	Briar
Works with no internet at all	✅	❌	❌	✅
No phone number required	✅	❌	✅	✅
Double Ratchet encryption	✅	✅	✅	✅
Encrypted voice calls	✅	✅	✅	❌
Steganography	✅	❌	❌	❌
Offline on-device AI	✅	❌	❌	❌
Bot API	✅	❌	❌	❌
Fully open source	⚠️ core	✅	✅	✅

Briar is the closest thing to OSHI and deserves the credit: it pioneered offline-first messaging on Android. OSHI brings the same idea to iOS, adds voice calls and a bot API, and is fully open about which parts you can audit.

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Bot SDK

pip install requests   # the SDK has no other dependency

from oshi_bot import OSHIBot

bot = OSHIBot(token="your-bot-token")        # created inside the OSHI app
bot.send_message(group_id="...", text="Deploy finished ✅")

@bot.on_message
def echo(msg):
    bot.reply(msg, f"You said: {msg.text}")

Full reference: sdk/README.md · docs/bot-api.md

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Security

Report a vulnerability privately: security@oshi-messenger.com Please do not open a public issue for a security bug.

Bug bounty, paid from a solo developer's own pocket, so the numbers are honest rather than impressive:

Severity	Example	Reward
Critical	Break the encryption, read messages you should not	$500
High	Bypass authentication, impersonate a user	$250
Medium	Leak metadata the protocol promises to hide	$100

Details and threat model: Security.md

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Contributing

Issues and pull requests are welcome — especially on the cryptographic core, where a second pair of eyes is worth more than a feature.

• Found a bug? Open an issue
• Read CONTRIBUTING.md before a pull request
• Not a coder? Starring the repository genuinely helps people find it

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Download

iOS and macOS. Android is in closed testing.

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_{Built by one person, in the open, because privacy should not require trusting a company.
MIT licensed · oshi-messenger.com}