Settings > Notifications > Notification Content > Show: "Name Only" or "No Name or Content"
I've had this enabled to prevent sensitive messages from appearing in full whilst showing someone something on my phone, but I guess this is an added benefit as well.
Yes. And technically, from a privacy perspective, it's even worse than that. What's additionally happening is they're still 'syncing' back to Apple servers via APNS (and to Alphabet servers via Firebase on Android)—even with notifications completely disabled, that's correct.
If the app generates them, the OS receives them. That's why the Signal app offers this setting.
>it's even worse than that. What's additionally happening is they're still 'syncing' back to Apple servers via APNS (and to Alphabet servers via Firebase on Android)—even with notifications completely disabled, that's correct.
Source? I don't think either OS implements notification syncing between devices, it's only one way, and as others have mentioned, the actually push notification doesn't contain any message content, only an instruction for signal to fetch and decrypt the message.
This sounds correct. When I implemented push notifications for an iPhone application, I remainder needing to obtain a store a separate token for each device a user has, and subscribing to a feed of revoked delivery tokens. Seemed like an interesting design intended to facilitate E2E encryption for push notifications.
With notifications disabled APNS push notifications fail for the sending app backend. The device id is rendered invalid if push notifications are disabled at any point. Backends are supposed to handle this and quit sending messages.
Each app gets its own device ID in which to send messages. Turning them off at the system level should invalidate all of them, but I have only tested that with my own work.
Signal has this setting to tell the backend how much information to put into the push message. It can tell the backend to send a simple notification saying “new message” and not send information through APNS or enable it.
I am willing to bet Signal has a notification extension to handle edge cases where there is lag in settings to scrub the message metadata before it dings a screen alert.
However, if this is important to you then you want Signal to stop telling Android to make the notifications. If it doesn't exist nobody will accidentally make it available.
Deleting that history is good to know about after the fact, but preferably lets just not create the problem.
It's a mode of the phone that is supposed to prevent cyber attacks, more so than "normal mode" I suppose, since it's supposed to limit features in the name of security. This seems like a variant of such attack, so seems like it should protect against it
There is a documented list of things that Lockdown Mode affects [1], this is not one of the advertised ones. There are a bunch of other (undocumented) things it affects (some of which are bugs :/), but I don't believe it has any affect on notification storage.
Mostly it seems the documentation is vague. Is there anything clearer than this?
> Web browsing: Certain complex web technologies are blocked, which might cause some websites to load more slowly or not operate correctly. In addition, web fonts might not be displayed, and images might be replaced with a missing image icon.
"Signal’s settings include an option that prevents the actual message content from being previewed in notifications. However, it appears the defendant did not have that setting enabled, which, in turn, seemingly allowed the system to store the content in the database."
Not sure if it's exactly the same, but I had to add a When notification arrives with <message>, do <action> event trigger in my Crank macOS app (https://lowtechguys.com/crank) so I can show you how to do it on macOS:
HOURS=6
EPOCH_DIFF=978307200
SINCE=$(echo "$(date +%s) - $EPOCH_DIFF - $HOURS * 3600" | bc)
sqlite3 ~/Library/Group\ Containers/group.com.apple.usernoted/db2/db \
"SELECT r.delivered_date, COALESCE(a.identifier, 'unknown'), hex(r.data)
FROM record r
LEFT JOIN app a ON r.app_id = a.app_id
WHERE r.delivered_date > $SINCE
ORDER BY r.delivered_date ASC;" \
| while IFS='|' read -r cfdate bundle hexdata; do
date -r $(echo "$cfdate + $EPOCH_DIFF" | bc | cut -d. -f1) '+%Y-%m-%d %H:%M:%S'
echo " app: $bundle"
echo "$hexdata" | xxd -r -p > /tmp/notif.plist
plutil -p /tmp/notif.plist 2>/dev/null \
| grep -E '"(titl|title|subt|subtitle|body|message)"' \
| sed 's/^ */ /'
echo "---"
done
Basically, notifications are in an sqlite db at ~/Library/Group Containers/group.com.apple.usernoted/db2/db and are stored as plist blobs.
In recent years, filesystem paths for system services have started to converge for both macOS and iOS so I'm thinking with jailbreak you could get read access to that database and get the same data out of it.
On android there are apps that let you see the history - i use NotiStar occasionally to see if i unwittingly dismissed important notifications. And i believe there are apps/settings that help you clear the history from the device.
But this is a reminder that these centralized notification infrastructure (FCM and APNs) store notification content (if the app is told to send content in it - signal with option enabled wouldn't send content) even if we clear local history these middleman still hold it
On android its quite easy. There is a page of a protocol address that has all notifications show. I used to have a seizure to it. It has been years since I was on android.
But it was really useful each time I did not see a notification in time.
Larping about security and complaining about companies responding to court orders only gets you so far. Its way more useful to look at what actually happens in reality.
I wonder why Apple doesn't 'just' delete the notification data associated with the app from the internal database when the user deletes the app? It seems like asking for problems to just keep old notification content around forever.
If the "database" works like most other databases (eg. postgres or sqlite), deleting a row doesn't immediately cause the data to be wiped from disk, for performance reasons. Then as others mentioned you have filesystem/SSD logic that does something similar on top of that.
If it never hits flash that might work, but if it's in flash storage then the block may not be erased by the time its dumped.
I'm not sure precisely how the NAND controller responds to requests for raw data from blocks with "deleted" data. And if this would require decapping the flash.
Some flash will happily let you see the data and delay erasing it.
Generally flash is non deterministic about when blocks even those with entirely stale data are erased . It might be years before the block is reused due to wear leveling algorithms and it might retain data that entire time.
Here's hoping the controller for phones which hold sensitive data are more active
It's one of those problems where as soon as someone notices, it's crazy that no one noticed. I can't imagine this not being overhauled going forward. It's just a bad way to operate and now it's news.
On Android, when I use WhatsApp and have notifications for groups turned off, I can still see that they arrive briefly and then get removed (the icon top left vanishes). I wonder often, if this is a way to push all group message content into an unencrypted data trace as well - for the same use case.
If the notification has the data, then yes. It's trivial to create an app that listens to notifications; Samsung even has one themselves called NotiStar that replicates the notification history feature that Android normally has.
“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
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.
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.
I thought Signal didn’t show message previews by default and you had to go in and enable it? I’ve never had message previews in my Signal and I don’t remember changing anything. Maybe when they introduced the feature, you could pick but they strongly suggested it not showing?
The opposite, actually. Signal endlessly nags you to turn on notifications, and when you turn them on, previews and content are shown by default. You cannot opt out of the nags.
There needs to be a bit more "group chat" control in Signal messages, wherein you could enforce certain settings for certain chats regardless of the phone settings. You could have group chats that would enforce not showing more information in the notifications, while others would still allow it.
I think it fits in pretty well with Signal. As it stands, a group chat can control when a message is automatically deleted for everyone, so everyone can rely on that being a shared setting. That's an intentional design decision. There's no individual opt-out.
An individual can disable name or content in notifications in iOS, or set "mute messages" for a chat to prevent notifications from appearing for that specific chat, but there's nothing that gives group members any assurance that other group members are doing that.
But it would be pretty well in line with the "I trust my contact with this communication, but only if they're not systematically misled to copy it to readily exploitable insecure storage" line of thinking.
Since the purposes of the program are pretty heavy on private communication, I'm inclined to think that takes precedence here, especially considering the consequences for dropping default message previews versus adding default reveal of supposedly private information.
The article you're commenting on is about people who obviously would have wanted this disabled, but didn't have it disabled, presumably because they didn't know about this issue.
Signal does not send any sensitive information in push notifications sent via APNs [0]. This story concerns the local OS cache of push notifications, which are triggered after E2E decryption has occurred.
Right. It's purely a protection against MitM snooping. The app has to have the messages in plaintext to display to you via whatever mechanism the OS uses. Seems obvious, but also not, at the same time.
I've found other ways Signal can leak information, even with disappearing messages. It's not the total install-and-be-done privacy screen that some people think it is, and requires a little effort at the user end to fill in a few gaps.
Good. The moment they add it, all kinds of apps will start to abuse it, for "sekhurity" (read: engagement) reasons. See e.g. all the apps that now disallow taking screenshots, for no legitimate reason.
Personally I'd be in favor of a hard app store policy, that if an app notifies you about something, all the importantdetails (like full message text) must be included - specifically to allow the user to view the important information without having to open the app itself.
thank god whatsapp doesn't do that either. or telegram. or allo back in the day, or every single mobile first messaging app
The only one I can think of that doesn't require a mobile login is iMessage, because it's not a chat app, it's lock in and data theft disguised as software
I've had this enabled to prevent sensitive messages from appearing in full whilst showing someone something on my phone, but I guess this is an added benefit as well.
Critical distinction, as merely changing OS notification settings will simply prevent notification content from being displayed on-screen.
If the app generates them, the OS receives them. That's why the Signal app offers this setting.
Source? I don't think either OS implements notification syncing between devices, it's only one way, and as others have mentioned, the actually push notification doesn't contain any message content, only an instruction for signal to fetch and decrypt the message.
Each app gets its own device ID in which to send messages. Turning them off at the system level should invalidate all of them, but I have only tested that with my own work.
Signal has this setting to tell the backend how much information to put into the push message. It can tell the backend to send a simple notification saying “new message” and not send information through APNS or enable it.
I am willing to bet Signal has a notification extension to handle edge cases where there is lag in settings to scrub the message metadata before it dings a screen alert.
Settings > Notifications > Messages > Show
Deleting that history is good to know about after the fact, but preferably lets just not create the problem.
But most likely (pure speculation mind you), this was a case of someone handing over the phone for review and where cooperating.
It might have been that they deleted signal some time ago, or even deleted signal and then handed over the phone.
It's notable that the data wasn't recovered from signals storage (was the data securely erased or that kind of recovery not attempted?).
[1] https://support.apple.com/en-us/105120
> Web browsing: Certain complex web technologies are blocked, which might cause some websites to load more slowly or not operate correctly. In addition, web fonts might not be displayed, and images might be replaced with a missing image icon.
Semi-related, in whatsapp reading the text in the notification doesn't mark the message as read, so the OS is kinda mitm here.
If piping encrypted content resulted in a plaintext notification then you'd have a right to be concerned.
"Signal’s settings include an option that prevents the actual message content from being previewed in notifications. However, it appears the defendant did not have that setting enabled, which, in turn, seemingly allowed the system to store the content in the database."
Second, how can I see this notification history?
In recent years, filesystem paths for system services have started to converge for both macOS and iOS so I'm thinking with jailbreak you could get read access to that database and get the same data out of it.
But this is a reminder that these centralized notification infrastructure (FCM and APNs) store notification content (if the app is told to send content in it - signal with option enabled wouldn't send content) even if we clear local history these middleman still hold it
If you drop a settings widget on your home screen, it will let you choose a specific area, including notifications.
I don't know if the output is the complete database.
But it was really useful each time I did not see a notification in time.
Hopefully, you meant to write "shortcut"...
Android > Settings > Notifications > Manage > Notification History
Court cases are the real way to audit security.
Larping about security and complaining about companies responding to court orders only gets you so far. Its way more useful to look at what actually happens in reality.
0. https://www.404media.co/fbi-extracts-suspects-deleted-signal...
I'm not sure precisely how the NAND controller responds to requests for raw data from blocks with "deleted" data. And if this would require decapping the flash.
Some flash will happily let you see the data and delay erasing it.
Generally flash is non deterministic about when blocks even those with entirely stale data are erased . It might be years before the block is reused due to wear leveling algorithms and it might retain data that entire time.
Here's hoping the controller for phones which hold sensitive data are more active
Photos I had long deleted were still in the backup! It's quite surprising just how much is being stored by the phone.
“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
i haven't actually seen signal or anyone adjacent recommend that previously though, idk where that claim came from
An individual can disable name or content in notifications in iOS, or set "mute messages" for a chat to prevent notifications from appearing for that specific chat, but there's nothing that gives group members any assurance that other group members are doing that.
Since the purposes of the program are pretty heavy on private communication, I'm inclined to think that takes precedence here, especially considering the consequences for dropping default message previews versus adding default reveal of supposedly private information.
They rest who "evaluate their threat models" can practice Spy-life-gymnastics by disabling it from Signal.
The article you're commenting on is about people who obviously would have wanted this disabled, but didn't have it disabled, presumably because they didn't know about this issue.
[0] https://mastodon.world/@Mer__edith/111563865413484025
I've found other ways Signal can leak information, even with disappearing messages. It's not the total install-and-be-done privacy screen that some people think it is, and requires a little effort at the user end to fill in a few gaps.
Personally I'd be in favor of a hard app store policy, that if an app notifies you about something, all the importantdetails (like full message text) must be included - specifically to allow the user to view the important information without having to open the app itself.
"To use the Signal desktop app, Signal must first be installed on your phone."
The only one I can think of that doesn't require a mobile login is iMessage, because it's not a chat app, it's lock in and data theft disguised as software