As mentioned in the comments, plain text keys aren’t bad because they are necessary. You have to have at least one plain text key in order to be able to use encryption
This is a, “it’s turtles all the way down!” problem. An application has to be able to store its encryption keys somewhere. You can encrypt your encryption keys but then where do you store that key? Ultimately any application will need access to the plaintext key in order to function.
On servers the best practice is to store the encryption keys somewhere that isn’t on the server itself. Such as a networked Hardware Security Module (HSM) but literally any location that isn’t physically on/in the server itself is good enough. Some Raspberry Pi attached to the network in the corner of the data center would be nearly as good because the attack you’re protecting against with this kind of encryption is someone walking out of the data center with your server (and then decrypting the data).
With a device like a phone you can’t use a networked HSM since your phone will be carried around with you everywhere. You could store your encryption keys out on the Internet somewhere but that actually increases the attack surface. As such, the encryption keys get stored on the phone itself.
Phone OSes include tools like encrypted storage locations for things like encryption keys but realistically they’re no more secure than storing the keys as plaintext in the application’s app-specific store (which is encrypted on Android by default; not sure about iOS). Only that app and the OS itself have access to that storage location so it’s basically exactly the same as the special “secure” storage features… Except easier to use and less likely to be targeted, exploited, and ultimately compromised because again, it’s a smaller attack surface.
If an attacker gets physical access to your device you must assume they’ll have access to everything on it unless the data is encrypted and the key for that isn’t on the phone itself (e.g. it uses a hash generated from your thumbprint or your PIN). In that case your effective encryption key is your thumb(s) and/or PIN. Because the Signal app’s encryption keys are already encrypted on the filesystem.
Going full circle: You can always further encrypt something or add an extra step to accessing encrypted data but that just adds inconvenience and doesn’t really buy you any more security (realistically). It’s turtles all the way down.
This reminds me of the apparent gnome-keyring security hole. It’s mentioned in the first section of the arch wiki entry: https://wiki.archlinux.org/title/GNOME/Keyring
Any application can read keyring entries of the other apps. So it’s pretty trivial to make a targeted attack on someone’s account if you can get them to run an executable on their machine.
Exactly. Discord token stealers have been around for ages but no one gives Discord flak about leaving that secret unencrypted.
Discord aren’t marketing themselves on secure or encrypted messaging. Signal is.
Very good “Explain Like I’m Five” there!
Signal seem to be the least compromising messenger app out there with their privacy policy and open source code base. It’s only natural they are frequent victims of FUD.
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Don’t phones have something comparable to a TPM?
The article referenced is about their Desktop application
I kind of agree that this may be a little overblown. Exploiting this requires device and filesystem access so if you can get the keys you can already get a lot more stuff.
A secure enclave can already be accessed by the time someone can access the Signal encryption keys , so there’s no extra security in putting the encryption keys in the secure enclave.
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It’s eventually going to have to be stored in plaintext somewhere. Where are you then putting the encryption key for the encryption keys and how do you start the chain of decryption without the first key?
Sorry, I don’t think I understand what you’re suggesting. Are you saying encryption keys should themselves be encrypted?
FYI this story isn’t about plaintext passwords, it’s about plaintext encryption keys to chat history.
I deleted my reply, because I don’t know what I’m talking.
Also not a surprise because as the article notes it’s been known and discussed since at least 2018
How else should the keys be stored?
There are system specific encryption methods like keychain services on iOS to store exactly this kind of sensitive information.
How would that provide additional security in the particular circumstance of someone having access to the Signal encryption keys on someone’s phone?
This particular scenario involves the MacOS desktop app, not the phone app. The link is showing just an image for me - I think it’s supposed to be to https://stackdiary.com/signal-under-fire-for-storing-encryption-keys-in-plaintext/
That said, let’s compare how it works on the phone to how it could work on MacOS and how it actually works on MacOS. In each scenario, we’ll suppose you installed an app that has hidden malware - we’ll call it X (just as a placeholder name) - and compare how much data that app has access to. Access to session data allows the app to spoof your client and send+receive messages
On the phone, your data is sandboxed. X cannot access your Signal messages or session data. ✅ Signal may also encrypt the data and store an encryption key in the database, but this wouldn’t improve security except in very specific circumstances (basically it would mean that if exploits were being used to access your data, you’d need more exploits if the key were in the keychain). Downside: On iOS at least, you also don’t have access to this data.
On MacOS, it could be implemented using sandboxed data. Then, X would not be able to access your Signal messages or spoof your session unless you explicitly allowed it to (it could request access to it and you would be shown a modal). ✅ Downside: the UX to upload attachments is worse.
It could also be implemented by storing the encryption key in the keychain instead of in plaintext on disk. Then, X would not be able to access your Signal messages and session data. It might be able to request access - I’m not sure. As a user, you can access the keychain but you have to re-authenticate. ✅ Downside: None.
It’s actually implemented by storing the encryption key in plaintext, collocated with the encrypted database file. X can access your messages and session data. ❌
Is it foolproof? No, of course not. But it’s an easy step that would probably take an hour of dev time to refactor. They’re even already storing a key, just not one that’s used for this. And this has been a known issue that they’ve refused to fix for several years. Because of their hostile behavior towards forks, the FOSS community also cannot distribute a hardened version that fixes this issue.
In the device’s secure enclave (e.g. TPM).
How does that help when somebody has access to the phone via your PIN or password?
If I’m not mistaken you can save keys in these chips so that they can not be extracted. You can only use the key to encrypt/decrypt/sign/verify by asking the chip to do these operations with your key.
That sounds only marginally better. Access to the phone still means you can create a backup containing the key, so TPM wouldn’t help much.
No, why would a backup contain non-exportable information? One of the reasons to use TPM to begin with is that sensitive information can’t leave it.
How do you restore a backup on another phone without the keys?
You would probably use a recovery key that exists exclusively elsewhere like on paper in a vault. Like bitlocker.
I have no idea if signal uses TPM or not but generally keys in TPM are non-exportable which is a very good thing and IMO the primary reason to use TPM at all.
One would hope the backup is encrypted.
It is. A password is generated that you have to write down. It must’ve been a compromise because they knew most people would just pick a shitty password if they didn’t generate one and it would end up on a piece of paper or in some digital form anyway.
After your edit, the post points to an image only, no longer the link to the source. Please edit back the link, if not at least into the body.
Fixed it! Thank you.
Isn’t Signal Open Source? If so, why is it a surprise then?
Its not a surprise but it has not really received a lot of attention since people have reported it.
https://github.com/signalapp/Signal-Desktop/issues/5751
Also signal as a service is not really open source because it is not selfhostable. The server backend is proprietary afaik.
The back end is open source, but sometimes they’ve lagged years behind releasing the source code. Other developers have stood up copies of the signal network. Session, for example.
You can self host your own signal, but it’s not federated, so you’d have nobody to talk to
So effectively its not FOSS.
It’s absolutely FOSS. It is not, however federated. But that is not a requirement to be free and open source software
Think of it like this, Linux is free and open source software, even if I don’t give you a shell on my computer.
You can use the code, however you want, in any project you want.
The back end is open source, but sometimes they’ve lagged years behind releasing the source code.
I think this is the more worrying part if true. The backend is licensed under the AGPL, so this would technically be a
violationof their terms- Remote Network Interaction; Use with the GNU General Public License.
Notwithstanding any other provision of this License, if you modify the Program, your modified version must prominently offer all users interacting with it remotely through a computer network (if your version supports such interaction) an opportunity to receive the Corresponding Source of your version by providing access to the Corresponding Source from a network server at no charge, through some standard or customary means of facilitating copying of software
Edit: For anyone else reading I looked into it a bit more and looks like the issue came to a head around 3 years ago, with this comment being made after a year of missing source code. The public repo has been pretty active since then, so the issue seems to be resolved
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It isn’t, because their business practices violate the four FOSS essential freedoms:
- The freedom to run the program for any purpose
- The freedom to study and modify the program
- The freedom to redistribute copies of the original or modified program
- The freedom to distribute modified versions of the program
Specifically, freedom 4 is violated, because you are not permitted to distribute a modified version of the program that connects to the Signal servers (even if all your modified version does is to remove Google Play Services or something similar).
The license does not prevent number four from happening, they just ask people not to do it
FYI Submitting an image in the Lemmy “create post” submittion form overrides the URL feild. I’m not sure if anyone submitted a bug about this.
Source? That’s just an image.
Restricting access to files within a user is why sandboxing is useful. It in theory limits the scope of a vulnerability in an app to only the files it can read (unless there is a sandbox escape). Android instead prevents apps from accessing other apps’ files by having each app run as a separate user.
One way to keep the encryption keys encrypted at rest is to require the login password (or another password) to open the app, and use it to encrypt the keys. That said, if an adversary can read Signal’s data, they can almost certainly just replace Signal with a password-stealing version.
The link is broken, but this is apparently an issue with Signal Desktop, not regular Signal. The proposed solution does not work on Windows: https://www.electronjs.org/docs/latest/api/safe-storage
[…] content is protected from other users on the same machine, but not from other apps running in the same userspace.
It’s unfortunately about the best you can do on Windows.
Thanks for the heads up on the broken link! I fixed it.
by any process on the system
This IS bad. Btw they can ask the user to type the password rather than saving it in a plaintext. I can’t believe comments on this thread defend Signal…
But can you trust that a user will pick a difficult to break password? They likely will pick something simple to remember but that is not a good password.
The we are just back to essentially having a plaintext password because if the attacker has a good dictionary, it will be easy to crack.