Security codes and key-change warnings

Your app gets your contacts' keys from our server. A security code lets you check that they are the right keys, without having to trust us.

Every contact has a 60-digit security code, shown as 12 groups of 5 digits, and a matching QR code. Your device computes it from both people's identity keys, so it is the same on both sides.

To check it, compare the code in person or over another channel you trust, or scan your contact's QR code with your camera. On the web you can also paste a code to compare it. If it matches, mark the contact as verified, and a verified mark appears in the chat.

In a group, every member has their own security code in the group settings.

The first time your device sees a contact's key, it remembers it. If the key changes later, your device itself shows "security code changed" in the chat, whatever our server says. For a contact you verified, a notice also appears above the message box, so you can compare codes again.

A key change never blocks sending. The decision stays with you.