Relayium — End-to-end encrypted peer-to-peer file transfer
Relayium is an open-source, end-to-end encrypted,
peer-to-peer (P2P) file 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
over the LAN or a pairing code need no account; creating a share link
or a stored download link requires the sender to sign in.
How it works
- Open relayium.com on two devices on the same network — they discover each other automatically.
- Pick a file or drag and drop (up to 1,000 at once); the receiver accepts.
- Both screens show a 6-digit verification code — compare it to rule out a man-in-the-middle.
- The file streams device-to-device, end-to-end encrypted, and is verified with a per-file SHA-256 hash.
Why Relayium
- End-to-end encrypted — per-transfer X25519 key exchange and AES-256-GCM; keys never leave the two devices.
- 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; realtime transfers need no account (share and download links require the sender to 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. Realtime transfers (LAN or pairing code) need no account; creating a share link or a stored download link requires the sender to 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 the connection may go through an encrypted relay 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).
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; in Firefox and Safari keep files under about 200 MB because they buffer in memory.
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.