Security News > 2021 > June > Signal app safety numbers do not always change — here's why
When you or your contact reinstall the Signal app or switch over to a new device, the Signal safety number between you two may not always change.
The safety number is a feature of the app that helps users verify the security of their messages and calls with their contacts, and is typically expected to change when either party reinstalls the app or switches devices.
Further, the researchers tested this behavior across multiple platforms currently supported by Signal, including Linux, OSX, Android, iOS, and Windows, and state that the safety numbers would not always change across these upon deletion and reinstallation of the Signal app, or when switching over to a different device.
In tests by BleepingComputer, the uninstallation and reinstallation of Signal app on Android and iOS devices did reset the safety number, and the contacts were notified of the safety number change.
The subsequent responses to researchers' reports by Signal provide us a better understanding of how Signal safety numbers work, when do they change, and when not.
"Verification of safety numbers is a good security practice for sensitive communication. If a safety number has been marked as verified, any change must be manually approved before sending a new message."