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Encrypted peer-to-peer messaging over Bluetooth mesh networks.

No internet. No servers. No carrier. No account. Just radios talking to radios.

Overview

Hoppr is a messaging platform engineered for environments where internet access is unavailable, degraded, or untrusted. Messages propagate device-to-device through a Bluetooth Low Energy mesh, requiring no centralized infrastructure, accounts, or identifiers.

Vision

Decentralisation has come in layers. Each one removed a dependency.

2009Bitcoinmoney without banks
2022Nostrspeech without platforms
2026Hopprmessaging without the internet

Bitcoin freed value from custodians. Nostr freed identity and publication from centralised hosts. Hoppr removes the last assumption: that a network has to exist at all. A phone without service, a city under blackout, a protest, a festival, a desert. The mesh still carries.

The same Bluetooth radio your device already has, used the way radios were always meant to be used: direct, local, and unowned.

Architecture

Devices within Bluetooth range establish peer sessions automatically.
Messages are relayed hop-by-hop through intermediate nodes toward the recipient.
All traffic is end-to-end encrypted using the Noise XX handshake pattern with Curve25519, ChaCha20-Poly1305, and Ed25519 signatures.
A dual-stack layer runs two parallel protocol variants on the same radio and the same relays. The Hoppr-native variant (service UUID F71E237E, Nostr kind 20100, tag hg, Noise prologue hoppr-mesh/1, packet version byte 0x02) keeps Hoppr-to-Hoppr traffic isolated. The public interop variant bridges to the wider open mesh population when the user enables it in Settings.

Reach Analysis

In a mesh of N devices with average node degree d, a gossip packet propagates to all peers in expected O(log_d N) hops. Under an asynchronous flood at uniform density, the expected number of devices reached after h hops is bounded by:

E[R(h)]  =  min( N ,  d · (d−1)^h−1 )

Field example. Five peers on average within Bluetooth Low Energy range (d = 5), default TTL of seven hops (h = 7):

E[R]  =  min( N ,  5 · 4⁶ )  =  20 480 devices

Duplicate packets are suppressed per device by a bounded LRU cache of 1000 recent message identifiers with a five-minute expiry. Lookups are O(1) and deterministic. To reconcile missed messages between peers on reconnection, each node exchanges a 400-byte Golomb-Coded Set summarising what it has seen. For a GCS encoding n elements at target false-positive rate p, the expected bits per element is:

bits / element  ≈  log₂( 1 / p )  +  1 / ln 2

Field example. With n = 200 recent identifiers and p = 0.01, each device advertises roughly 200 · 8 ≈ 1600 bits of state, or about 200 B encoded. Under 1% false-positive pressure, a 400-byte summary carries on the order of 400 message identifiers before a peer must ask for the full set.

In practical terms: a packet released into a moderately dense mesh reaches thousands of devices within seconds of radio time, while each individual device rejects duplicates exactly, and missed messages are healed on reconnection through a sync envelope smaller than a single TCP segment.

Capabilities

Mesh-first architecture. Built on the transport layer. Social graphs, feeds, and recommendation systems are absent by design.
End-to-end encryption. 1:1 direct messages use a Noise XX handshake. Mesh broadcasts are signed packets. Nostr fallback uses NIP-17 gift-wrap.
Dual transport. Automatic fallback to Nostr relays routed over the Tor network (via Arti) when mesh connectivity is unavailable.
Adaptive relay control. Seven-hop default TTL with probabilistic forwarding at elevated peer density to conserve battery without reducing reach.
GCS gossip sync. A 400-byte Golomb-Coded Set reconciles missed messages between peers on reconnection at a 1% false-positive rate.
QR peer verification. On-device live-camera scan compares Ed25519 and Noise identity fingerprints before a session is trusted.
Geohash channels. Location-scoped public rooms and location notes ride the Nostr transport.
Message toolkit. Emoji reactions, message edit, delete, pin, and star across DMs and channels.
Rich text. Inline Markdown with fenced code blocks and inline code.
On-device intelligence. Local translation and channel summarization run without leaving the device.
Privacy controls. Privacy shield in the app switcher, stealth mode, and a Privacy PIN with decoy identity.
Lightning integration. Zaps receive via NIP-57 and pay-to-message bonds for unsolicited DMs.
Multi-device. Encrypted backup and QR onboarding bring a second device online without a server.
Live mesh topology. Real-time visualizer of peers, hops, and link quality in the current radio neighbourhood.
macOS polish. Menu-bar quick-compose and sticker packs on the native desktop build.
Panic wipe. A single gesture destroys keys, message caches, and identity state on the device.
Slash commands. IRC-style controls: /who, /fav, /block, /unblock, /me, /slap, /help.
Payment chip detection. Lightning bolt11, LNURL, and Cashu tokens are recognised inline and tappable to open a wallet.
iOS Share Extension. Share text and links from Safari or any app directly into the mesh.
Native macOS app. Same codebase. Shipping since v1.5.
Efficient runtime. Approximately 12 MB installed footprint. Cold launch under 400 ms on iPhone 12.
Data minimization. No telemetry, crash reports, or advertising identifiers are transmitted from client devices.

Feature Highlights

On-device AI. Translation and channel summarization run locally, so nothing about your conversation leaves the device.
Lightning-native. Receive zaps over NIP-57 and gate inbound DMs with pay-to-message bonds priced in sats.
Live mesh graph. Watch peers, hops, and link quality redraw in real time as the radio neighbourhood changes.
Dual-stack mesh. Hoppr-to-Hoppr traffic runs on a dedicated protocol identifier set. An optional toggle bridges to the wider public mesh for reach without blending the conversation spaces.

Lean by design

Other chat apps assume a flat-rate data plan and a flagship device. Hoppr does not. Every default is tuned for users on metered networks, weak batteries, and old hardware.

Installed size: under 12 MB on iOS and macOS, target under 20 MB on Android
Voice notes: AAC mono at 8 kHz, around 1 kB per second
Images: resized to 1080 px long edge, re-encoded to WebP, stripped of EXIF
Text messages: typically under 300 bytes on the wire after Noise framing
Auto-cleanup: messages older than 30 days are purged locally by default, user-configurable
Storage cap: local SQLite store is capped at 50 MB, rotates oldest out
Low data mode: a single toggle disables the Nostr fallback entirely so the app sends nothing over the internet
Telemetry: none. no analytics SDK, no crash reporter, no advertising identifier

This is a deliberate limit, not a shortcut. Reach matters more than richness when the device is the only link the user has.

Technology

The stack is intentionally narrow and auditable.

Transport (primary): Bluetooth Low Energy mesh. Dual-advertise, dual-scan. Seven-hop default TTL with adaptive probabilistic forwarding at elevated peer density.
Transport (fallback): Nostr over Tor via Arti (Rust, arm64 static library on iOS and macOS, JNI on Android). Gift-wrapped direct messages under NIP-17.
Handshake: Noise XX with Curve25519 key agreement, ChaCha20-Poly1305 authenticated encryption, Ed25519 signatures, SHA-256 hashing. Per-variant prologue binding.
Packet format: TLV body with an outer protocol-version byte. 0x01 is the public interop variant, 0x02 is Hoppr-native.
Dedup: Bounded LRU cache of 1000 recent message identifiers with five-minute expiry. Reconciliation via 400-byte Golomb-Coded Set at a 1% false-positive rate.
Persistence: SQLite via stdlib bindings on iOS and macOS. Equivalent on-device storage on Android. No cloud database.
Keys on iOS and macOS: Apple Keychain with kSecAttrAccessibleAfterFirstUnlockThisDeviceOnly. Never synced to iCloud. Wiped by identity reset.
Nostr relays: Public infrastructure. Subscriptions span kinds 20000, 20001, 20100, and 20101 across the g and hg geohash tags.
Build: iOS 16 plus, macOS 13 plus, Android 10 plus (API 29 plus). No third-party analytics, advertising, or crash-reporting SDKs.

Blog

Signed, long-form notes published by the Hoppr team on protocol design, mesh research, and release notes. Readable without an account, verifiable on any Nostr client.

Open the blog launching soon

Roadmap

v1.6 to v2.1Shipped in current build. Settings, reactions, threads, disappearing DMs, zaps receive, voice notes and images.live
v2.2Voice rooms in geohash channels.2 to 3 weeks
v2.3Hardware key identity (YubiKey NFC).3 to 4 weeks
v2.4Voice and video calls via NIP-100.4 to 6 weeks

Every release is signed. Pre-release builds are not distributed outside of closed testing programmes.

Technical Specifications

Transport: Bluetooth Low Energy mesh
1:1 DMs: Noise XX handshake
Mesh packets: Signed broadcast
Key agreement: X25519 (Curve25519)
Encryption: ChaCha20-Poly1305
Signing: Ed25519. secp256k1 Schnorr for Nostr
Hashing: SHA-256
TTL: 7 hops default. Fragment-relay cap 5
Dedup cache: LRU 1000 entries. 5 min expiry
Gossip sync: 400 B Golomb-Coded Set. 1% FPR
Voice codec: AAC. M4A. 16 kHz mono 16 kbps
Online relay: Nostr via Tor (Arti)

Availability

Early builds are public. Expect rough edges and breaking changes. See the download page for direct installers.

macOS alpha Deep debug build. Unsigned DMG. Expect crashes and UI gaps. Apple Silicon only for now.
Android, direct APK beta arm64 sideload outside the Play Store. Core mesh and protocol are live. Some feature screens still missing.
Android, Google Play coming soon Review in progress.
iOS coming soon App Store submission in progress.
Linux coming soon Native GTK build. Flatpak plus tarball.
Windows coming soon Signed MSIX installer.