Siabra

Siabra is a messenger whose private chats are protected by end-to-end encryption: a message is encrypted on your device and decrypted on your contact's. The keys never leave the phone — the server stores and forwards an opaque block and cannot read it.

Not everything here is encrypted, and we say so plainly — here and in the app.

WHAT THIS VERSION HAS
• One-to-one chats with end-to-end encryption
• Encrypted groups up to 256 members: roles, adding and removing, ownership transfer
• Closed and open groups — no member limit and no encryption
• Channels, closed and public: owner and admins post, everyone else reads. A public one is readable on the web without signing in; channels are not encrypted
• Saved Messages — encrypted notes to yourself
• Siabra, an AI assistant: everyone gets their own chat with it, unencrypted. It sees images you send, hears voice messages and draws on request
• One-to-one audio and video calls
• Image attachments — in encrypted chats and the assistant chat, up to 8 MiB per file
• Stories that last a day: seen by your contacts and people you have written to; not by those you blocked
• Voice messages up to five minutes
• Notifications: your device puts the name and text together, not the server
• Light and dark theme
• Interface in seven languages, English among them

WHAT IS ENCRYPTED AND WHAT IS NOT
Encrypted: one-to-one chats, encrypted groups, Saved Messages and their attachments.
Not encrypted: closed and open groups, channels, and the chat with the assistant. These messages are stored on the server in plain text, and reading them is technically possible if needed. "Closed" means an outsider cannot open the chat — not that it is encrypted. Which chat you are in is shown next to the input field, as you type.
Everything you send the assistant — text, images, voice — also leaves our server for the model provider that prepares the reply, and attachments there are not encrypted. Nothing else goes there: no name, no phone number, not a single message from any other chat.

HOW THE ENCRYPTION WORKS
The session is established with X3DH; symmetric encryption is AES-256-GCM. All encrypted chats — one-to-one, group and Saved — use Sender Keys: every device has its own sender chain, and the chain key travels to the recipient in an envelope sealed to their key, so your chats open on all your devices. The price, plainly: unlike the Double Ratchet, this scheme does not heal itself after a key is stolen. Audio and video are encrypted between devices (DTLS-SRTP); the devices agree on the keys. The 256-member limit applies to encrypted groups only: the chain key goes to each member pairwise. Where there is no encryption there is no limit.

WHAT ENCRYPTION DOES NOT HIDE
We promise no anonymity: signing in requires a phone number. The server sees who wrote to whom and when, the size of the encrypted block, when a device was last online, group membership, and for calls — who called whom, how long. If a direct connection fails, the call goes through our relay: it does not hear the conversation, but sees both addresses and the data volume. If you turn on address book sync, the server keeps your contact list — who knows whom; only you turn it on, and turning it off erases it. All of this is in the privacy policy: siabra.by/privacy.html

LIMITS WE PREFER TO SAY UP FRONT
• Group membership is confirmed by the server, not by encryption — check the member list yourself.
• Someone removed from a group can still decrypt messages already received — they got those keys legitimately as a member. Chain rotation cuts off only new ones.
• Saved Messages are encrypted with this device's keys: your notes won't open on another device.
• No calls in groups or channels, and the assistant cannot be called.