Signal App Safety Numbers Remain Unchanged When Reinstalling the App
security system researchers made an interesting finding while using Signal apps across multiple platforms, as they discovered that when you or your contact reinstall the Signal app or switch over to a new device, the Signal safety phone number between you two may not always change .
This specific safety number is a sport helping 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 .
end-to-end encrypted messaging apps like Signal function by having a security feature called “ condom number, ” or a “ security code, ” that can sometimes be represented as a QR code.
This SN is shared between you and every contact you have on Signal. The Safety Number ( SN ) serves as the pair ’ s fingermark and therefore helps both contacts to verify the privacy of their communications .
The SN is represented both in a human-readable numeric class and a QR code, and the expectation is that when a contact reinstalls the message app, switch to a new device, or change phone number, the condom act, and inherently the QR code, are expected to change .
The most common scenarios where a safety number advisory is displayed are when a liaison switches to a new call or re-installs Signal. however, if a safety issue changes frequently or by chance it may be a sign that something is ill-timed .
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unfortunately security researchers Kelly Kaoudis, John Jackson, Sick C odes, and Robert Willis have discovered, when installing Signal on a new device and transferring their account over, the fact that the condom number for their contacts and them didn ’ thyroxine change .
The researchers went ahead and tested this behavior across multiple platforms that are presently supported by Signal, like Linux, OSX, Android, io, and Windows, and discovered that the base hit numbers did not constantly change across these platforms when the Signal app was deleted and reinstalled, or when switching to a unlike device .
Mid-May, I got a new call. At the prison term I understood that with any change to the device or initiation of either party in a new world chat with message history, the Signal chat safety number changes .
This used to be but ( following an imply electronic mail back-and-forth with the Signal team over the course of a calendar month ) is no retentive reflected in the Signal corroborate documentation .
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Since their report of this emergence to Signal, the researchers state that the issue was cryptically resolved, claiming that Signal rolled out patches that they believe were responsible for resolving the issue .
It ’ randomness worth noting that Signal has revised its accompaniment documentation :
The most coarse scenarios where a condom number advisory is displayed are when a contact switches to a raw call or re-installs Signal, but these actions don ’ thymine always result in a guard number change .
Signal declared for the journalists at BleepingComputer that no changes have been made to the source code that regards safety numbers .
The VP of Engineering for Signal, Jim O ’ Leary stated that any updates made recently were separate of the normal alimony updates, and explained why condom numbers may not change as expected in all circumstances .
Signal ’ s CEO, Moxie Marlinspike shed some unaccented on the circumstances in which the base hit numbers will not change :
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It doesn ’ metric ton seem like you did. You tried ( and reported ) installing on a new device using Signal device transfer, and you tried cycling a linked device. These do not result in SN change notifications, because the underlie cardinal material has not changed, so there is nothing to warn .
— Moxie Marlinspike ( @ backbone ) June 5, 2021
In the same Twitter conversation, Marlinspike adds that the researchers ’ report covers a subject of Signal device remove, followed by the cycling of connect devices .
however, when uninstalling or reinstalling Signal on an unlinked device, the Safety Numbers are supposed to change, and that “ this is how it always worked and was supposed to work. ”
Read more: A Few Thoughts on Cryptographic Engineering
If Signal patched any issues described in the composition without announcing should be easy to find out given the fact that they are an open-source app, therefore their GitHub entrust history would reveal the changes :
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With the original determination of the condom numbers existence being to allow users to verify the security of their messages and calls with specific contacts, you should pay attention if the Safety Number between you and your contact changed, but not every individual case of app re-installation or migration may lead to a safety number change .