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Comment by frizlab | Hacker News Reader

Aren’t notifications supposed to be encrypted for Signal?

iOS stores the previously displayed notifications in an internal database, which was used to access the data. It’s outside of Signal’s control, they recommend disabling showing notification content in their settings to prevent this attack vector

They do control the content on the notification. It's a bit odd to put the sensitive text in the notification only to recommend disabling it at the system level.

They do not. They send encrypted notifications. It’s the OS that stores them unencrypted. It’s the OS at fault here IMHO.

i think they're replying to the "recommendation" part -- if it was recommended, why isn't it the safe default?

i haven't actually seen signal or anyone adjacent recommend that previously though, idk where that claim came from

Sorry, the “recommended” was a bad wording on my part. The recommendation comes from the 404 Media article who did the expose on this incident, not Signal itself.

I’ve checked the Signal documentation page, and there’s no mention of the privacy implications of the setting: https://support.signal.org/hc/en-us/articles/360043273491-In...

Signal does NOT send encrypted notification, they send a blank notification that act like a ping, the actual encrypted data is then fetched by the app itself.

No. They recommended disabling it at the app level. Only the Signal app can control whether the message contents are included in the notifications.

You can choose what to show in the notification and there is an option to include the message, so I'm guessing that allowed some unencrypted incoming messages to be read.

Sibling comment explains. The notification does arrive encrypted and is decrypted by an app extension (by Signal), however, if the message preview is shown, it is stored unencrypted by iOS. It is that storage that is accessed.

it seems iOS will drop previews into an unencrypted section. which, Is how I expected iOS notification previews to work without unlocking the phone

This kind of vulnerability is not tied to Signal but all apps which send notification.

They are;

“Messages were recovered from Sharp’s phone through Apple’s internal notification storage—Signal had been removed, but incoming notifications were preserved in internal memory. Only incoming messages were captured (no outgoing).”

ie the messages recovered were 1. incoming 2. stored by the OS after decryption

i also was spooked by the headline :p

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