Sharing & sending
Sync & device transfer
Keep your own devices in step without handing anyone your plaintext. The Sync & Offline tab holds three tools (offline pins, encrypted clipboard sync, and folder sync) while a separate Transfer tab streams a file straight from one device to another.
Offline pins
Offline pins let you mark specific files to keep available on a given device. Pinning is per device: each browser is given its own random device id (kept locally on that device), and your pins are recorded against that device, so every device keeps its own list, and pinning or unpinning on one doesn’t change the others.
- •Pick a device: the tab shows the current device’s short id, so you can tell which device you’re pinning for.
- •Pin or unpin: toggle any file in your vault to add or remove it from that device’s offline list.
- •Stays private: a pin only records which file you want kept on hand, the file itself stays encrypted, exactly as it is in your vault.
Encrypted clipboard sync
Clipboard sync keeps a short, shared history of small snippets available across the sessions where you’re signed in. Add a snippet on one device and it appears on the others in real time, ready to copy.
- •Item types: text and links. A snippet that is a lone
http(s)URL is tagged as a link; everything else is text. The web tool captures typed or pasted text only, there is no image capture. - •Size: up to 512 KB per snippet.
- •Retention: each snippet is deleted automatically 24 hours after you add it, and only your most recent snippets are kept (the server retains the latest 30).
How clipboard sync works
Each snippet is encrypted in your browser with a 256-bit AES-GCM key before it’s sent. That key is generated on your device and stored only in the browser, it never leaves the device and is never sent to the server. When you add a snippet, the server stores only the ciphertext plus lightweight metadata (its id, type, size, and timestamp) and pushes a live SSE (server-sent events) “clipboard” event to your other signed-in sessions so they can pull it. Fetching a snippet returns the ciphertext, which is decrypted locally.
What the server sees
The server only ever holds the snippet as ciphertext and the metadata it needs to wake up your other sessions. It never receives the encryption key and cannot read a snippet’s contents.Each device needs the same key
Because the key lives only in the browser and isn’t synced by the server, a device has to hold the matching key to read a snippet. A device without it will show a “different device key” notice instead of the plaintext, the trade-off of keeping the key entirely on your side.Folder sync
Folder sync lets you register local folder paths that the zcrypt desktop client should back up automatically. The web app is only for configuration: you add a folder path and an optional label, and toggle each one active or paused. The browser never reads or uploads the files in those folders, that work is done by the desktop client.
The backup runs while the desktop app is open on the device where those folders live.
Removing a folder
Deleting a folder configuration only stops future syncing for it. Files that were already backed up stay in your vault.Device-to-device transfer
The separate Transfer tab streams a file from one device to another in real time through a relay that stores nothing. The sending device gets a 6-digit room code and a separate pairing key. Scan the QR code (or open the link), or type both on the receiving device, and the file flows while both stay connected.
- •Encrypted before it leaves: the file and its name are encrypted in your browser and sent in small chunks over a WebSocket relay. The key is derived from the pairing key, which travels only in the QR code, link fragment or what you type, never through the relay.
- •Confirmation code: both screens show the same short code once paired. If they differ, stop and start a new room.
- •Nothing stored: the relay keeps the pairing room only in memory, and it can still see that a transfer happened and roughly how large it is; the room is torn down as soon as the transfer finishes, and an unclaimed room expires after about 10 minutes.
- •Both online at once: because the file streams straight between the two devices, both must be connected at the same time. If the connection drops mid-transfer, just start a new room.
Recipient not online?
Device-to-device transfer needs both ends connected together. If you need someone to pick a file up later, use Anonymous Send or a share link instead, both store the encrypted file so the recipient can fetch it on their own schedule.