FAQ

Short answers to the questions people ask first about Concord: servers, data, recovery, offline delivery, bots and security.

The full user manual starts at Getting started.

#Is there a server?

No server holds accounts or messages. Peers connect to each other directly. A rendezvous node is optional: it helps two peers behind home routers find and reach each other, and relays ciphertext when a direct connection fails. Anyone can run one, and a group only needs one.

#What can a rendezvous see?

Which identities connect through it, their IP addresses, and when. It cannot read messages, attachments or calls. DESIGN.md §6 goes through it service by service.

#Where is my data?

On your devices: ~/.config/concord on Linux, ~/Library/Application Support/concord on macOS, %AppData%\concord on Windows, or wherever CONCORD_HOME points; see Where your data is. Message bodies and your identity seed are encrypted at rest under your passphrase.

#What if I lose my device?

If the account is linked on another device, link the new one from it and your guilds and history come with it. Otherwise restore from the 24-word recovery phrase shown when the identity was created (Settings → Account → Recovery phrase shows it again). The phrase restores your identity only: the new device starts with no guilds and no history, so ask someone in each guild for a fresh invite, then restore a backup file (Settings → Account → Backup & restore) if you made one. Without the phrase and without another linked device, the identity cannot be recovered; there is no one to ask.

#Do messages arrive while I am offline?

If a rendezvous is set, every message, in a guild or a direct message, is also deposited, encrypted, in the rendezvous mailbox of each member device that is offline, and collected when that device comes back. The mailbox keeps them in memory for up to 14 days. Anything it does not hold is synced from whichever members are online when you reconnect.

#Do I get notifications on Android when the app is closed?

With Stay connected on (the default, under Settings → Notifications & sounds), a foreground service keeps the node running and messages arrive as they are sent. Push wakes through a third-party service are optional and off unless a build is configured for them; see PUSH.md.

#How big can a guild be?

Concord is built for friend groups and communities. Calls are a full mesh, where every participant sends to every other, which suits a handful of people per call.

#What cryptography does it use?

Ed25519 identities, MLS (RFC 9420) for every guild and direct message, and DTLS-SRTP for calls. The vendored MLS library and its local changes are listed in THIRD-PARTY-NOTICES.md; what is and is not protected is in DESIGN.md §13.

#Can I bring an existing community's history?

Yes. A guild owner can import a chat-history export into a signed, encrypted archive that every member can scroll back through. It is in guild settings, under Data → Import a chat archive.

#Can I run bots?

Yes. A bot is a peer with its own identity that you invite like anyone else. The headless build (make cli) has a --bot mode that speaks newline-delimited JSON on stdin and stdout; see BOTS.md.

#Why does Windows warn about the download?

The binaries are not code-signed. WINDOWS.md explains the warning and the alternatives. Every release is listed in SHA256SUMS with an Ed25519 signature, and the app verifies that signature before updating itself.

#How do I report a security problem?

Privately; see SECURITY.md.