Relayium — End-to-end encrypted peer-to-peer file and text transfer
Relayium is an open-source, end-to-end encrypted,
peer-to-peer (P2P) file and text transfer tool that runs entirely in your
browser. In realtime mode, files stream directly from one device to
another over a WebRTC DataChannel — on the same network they
never touch any server; across networks they pass
only through an encrypted relay that sees nothing but
ciphertext. An optional stored download-link mode encrypts files
in your browser (AES-256-GCM) before any upload, so the server holds
only zero-knowledge ciphertext. There is no installation, and no
server-imposed file-size limit in realtime mode. Realtime transfers
on the LAN need no account. Creating a cross-network pairing code for
files or text requires sign-in; joining with a code does not. Creating
a stored download link also requires sign-in.
For text, open a separate live peer session and send a note, link,
command or multiline code block while both devices are online.
Messages are end-to-end encrypted and Relayium keeps no session history:
its servers keep no message bodies or server-side history, and there is
no offline delivery. What the receiving device does with
a message after it arrives — copying or saving it — is up to that
device. Each message can be up to 65,536 UTF-8 bytes.
How it works
- Open relayium.com on two devices on the same network — they discover each other automatically.
- Pick files (up to 1,000 at once), or choose “Send a message” for text; the receiver accepts.
- Both screens show a 6-digit verification code — compare it out of band to detect X25519 endpoint public-key substitution or a signaling server impersonating an endpoint and terminating the application-layer end-to-end encryption. This authenticates the endpoints; it does not prove that the network path contains no server or TURN relay.
- Files or text move end-to-end encrypted; files also receive a per-file SHA-256 integrity check.
Why Relayium
- End-to-end encrypted — per-transfer X25519 key exchange and AES-256-GCM; keys never leave the two devices.
- Files and ephemeral text — send links, commands and multiline code without first making a file; text needs both devices online, Relayium servers keep no message bodies or server-side history, and each device can copy or keep what it receives.
- Peer-to-peer on your network (realtime mode) — on the same network, file bytes flow over WebRTC directly between devices and never pass through the server, which only helps the devices find each other; across networks they pass only through an encrypted relay that sees nothing but ciphertext. An optional stored download-link mode keeps files as zero-knowledge ciphertext only you can decrypt.
- Man-in-the-middle protection — a 6-digit Short Authentication String (SAS) on top of WebRTC's DTLS.
- Cross-platform — works between Windows, macOS, Linux, Android and iOS through any modern browser (Chrome, Edge, Firefox, Safari).
- Free and open source — AGPL-3.0 licensed, no install; same-network file and live text transfers need no account. Creating a cross-network file or text pairing code requires sign-in; joining with a code does not. Creating a stored download link also requires sign-in.
How Relayium compares
- vs AirDrop: cross-platform and browser-based, not limited to Apple devices — works between, e.g., a Windows PC and an iPhone.
- vs WeTransfer or Google Drive: in realtime mode, files move end-to-end encrypted with no stored server copy and no server size cap — directly device-to-device on the same network, or through an encrypted relay that only ever sees ciphertext across networks; the optional stored download-link mode encrypts files zero-knowledge before any upload so the server never sees plaintext.
- vs Snapdrop / PairDrop: adds an application-layer end-to-end encryption layer (X25519 + AES-256-GCM) and a SAS verification code, so a malicious signaling server cannot read or MITM the transfer undetected.
Frequently asked questions
Is Relayium free?
Yes — free and open source (AGPL-3.0), with no installation. Same-network file and live text transfers need no account. Creating a cross-network pairing code for files or text requires sign-in; joining with a code does not. Creating a stored download link also requires sign-in.
Do my files get uploaded to a server?
On the same network: no — files stream directly between the two devices over WebRTC and never touch the server. Across networks, browser sessions use an encrypted TURN relay by design that only ever sees ciphertext. There is also an optional stored download-link mode where your browser encrypts files before upload and the server stores only zero-knowledge ciphertext (AES-256-GCM, key only in the URL fragment).
Can I send text instead of a file?
Yes. Two online devices can open a separate end-to-end encrypted message session for text, links, commands or multiline code. Both devices stay online for the session; Relayium servers keep no message bodies and no server-side history, and there is no offline delivery. Each device can still copy or keep the text it receives. Each message can be up to 65,536 UTF-8 bytes; send anything larger as a file.
Is it end-to-end encrypted?
Yes — X25519 key exchange and AES-256-GCM, with keys that never leave the two devices, plus a 6-digit code to detect man-in-the-middle attacks.
Can I send files between different operating systems?
Yes — it is browser-based, so Windows ↔ iPhone, Android ↔ Mac, and Linux ↔ anything all work.
What is the file-size limit?
No server-imposed limit. Chrome and Edge stream files to disk; Firefox and Safari buffer in memory, so Relayium warns above roughly 256 MB — a conservative estimate, not a hard limit.
Learn more
Also available in: 中文 · 日本語 · 한국어 · Deutsch · Français · العربية · Español · Português
Source code on GitHub.
A machine-readable summary for AI engines is at
/llms.txt.