7 ms·

Yeah, I don't see how this is devastating for WhatsApp - you simply verify the other party's key once and then good to go, if it ever changes you'll get a big s

Yeah, I don't see how this is devastating for WhatsApp - you simply verify the other party's key once and then good to go, if it ever changes you'll get a big scary warning (you'll get that anyways but you should still verify the key in case your initial session was compromised). Admittedly I've only worked with Signal, but I'm assuming WhatsApp offers similar as they hired the same devs. Am I missing something here? I don't see how this attack would be useful against end-to-end encrypted messaging apps (well, properly implemented ones at least).

dingaling 10y ago
> you simply verify the other party's key once and then good to go Against what, though? The key that Whatsapp asserts is valid for the other user? As far as I am aware there's no way to access and visually eyeball-compare the raw keys in Whatsapp, just what the app presents as a signature or QR code. Open to correction.
- ultramancool 10y ago
  > Against what, though? The key that Whatsapp asserts is valid for the other user? No, against the other person sitting at the table with you via QR code scanning. Or their voice speaking the public key via another channel. > just what the app presents as a signature or QR code. Open to correction. What's wrong with the QR code? That QR code is a hash of the public key and exactly what you need for this identity verification purpose. If the pubkey changes after you've scanned it, you know you've got to verify that person again before sharing anything private over that channel.
  - geocar 10y ago
    > What's wrong with the QR code? That QR code is a hash of the public key I have no way to verify that. If WhatsApp is trustworthy and secure, then the QR code might be a hash of the public key, but to be completely frank, it could be anything. * I don't have the source code. * Nobody I know has the source code * Nobody I know has bothered to jailbreak their device and/or decompile the binary. I just got an update recently, and my friends are busy. If I had access to my own public and private key, I (or someone I know) could conceivably verify that I'm using it by decrypting my messages using another device (e.g. using wireshark). I appreciate that you might have the source code, or know someone with the source code, or might have reverse engineered the most recent update and have more confidence than I do, but you cannot transmit that confidence to me by simply insisting that it is the hash of the public key.
    - ultramancool 10y ago
      > If WhatsApp is trustworthy and secure, then the QR code might be a hash of the public key, but to be completely frank, it could be anything. Sure, but we're talking about this specific attack's effect on WhatsApp, if you want to debate the relative merits of open source vs closed source End-To-End encryption tools, you may have a point, but it's not one that's relevant here as it has nothing to do with this attack. Unless the attack can be used to update the app or something with a modified malicious version. Say it were Signal instead of WhatsApp if you must. Is there any effect made by this attack?
      - geocar 10y ago
        > Say it were Signal instead of WhatsApp if you must. Is there any effect made by this attack? This is what's known as a false dichotomy. Both systems are as implemented not secure from this attack for the reason I just said.
    - moxie 10y ago
      The source code is for generating the QR code is online here: https://github.com/WhisperSystems/libsignal-protocol-java/blob/master/java/src/main/java/org/whispersystems/libsignal/fingerprint/ScannableFingerprint.java https://github.com/WhisperSystems/libsignal-protocol-java/bl...
      - yownie 10y ago
        thanks moxie.
      - geocar 10y ago
        How do I know that is what is on my device?
    - startling 10y ago
      > If WhatsApp is trustworthy and secure, then the QR code might be a hash of the public key, but to be completely frank, it could be anything. The problem being solved here is validating that another Whatsapp user's key belongs to a flesh-and-blood person you know. We're taking it on faith at this point that Whatsapp's application is trustworthy. If it's not, validating keys is useless -- the app could upload all your chat transcripts in the background for all we know.
- moxie 10y ago
  Check out the image at the top of the post: https://whispersystems.org/blog/whatsapp-complete/ https://whispersystems.org/blog/whatsapp-complete/
williamscales 10y ago
I think WhatsApp has the big scary warning when keys change disabled by default. You can enable it for yourself but it's buried in the settings.
- avar 10y ago
  For anyone looking for it: Settings -> Account -> Security -> "Show security notifications = on".
  - mtgx 10y ago
    I hope Moxie can share with us why this feature is disabled by default. Does Whatsapp really think the notification would quickly become very annoying for regular users? How often would someone's closest friends really change their phones or uninstall Whatsapp? I imagine not that often for this to be a huge inconvenience, which is why I don't understand why the setting is off by default. Maybe it's something else I'm missing, which is why it would be good for Moxie or Whatsapp to clear up this puzzling choice. Also I hope both the Whatsapp and Signal teams think of ways to encourage security code authentication through better UI. Viber, for instance, has taken an interesting approach to encouraging easier authentication. It probably still doesn't go far enough to make it easy enough for just about anyone to want to authenticate their contacts, but I'd like to see more of this sort of UI experimentation: https://support.viber.com/customer/portal/articles/2017401-viber-security-faq https://support.viber.com/customer/portal/articles/2017401-v...
    - sievebrain 10y ago
      He has said before that key changes in the wild are an extremely common event. I imagine even just the notification that chats are now encrypted caused a lot of confusion and upset given the enormous size of the userbase. Spamming users with warnings that 99.9999% of the time will not be understandable let alone actionable is a quick way to get another SSL warning dialog scenario.
      - feld 10y ago

dingaling 10y ago

> you simply verify the other party's key once and then good to go Against what, though? The key that Whatsapp asserts is valid for the other user? As far as I am aware there's no way to access and visually eyeball-compare the raw keys in Whatsapp, just what the app presents as a signature or QR code. Open to correction.

ultramancool 10y ago
> Against what, though? The key that Whatsapp asserts is valid for the other user? No, against the other person sitting at the table with you via QR code scanning. Or their voice speaking the public key via another channel. > just what the app presents as a signature or QR code. Open to correction. What's wrong with the QR code? That QR code is a hash of the public key and exactly what you need for this identity verification purpose. If the pubkey changes after you've scanned it, you know you've got to verify that person again before sharing anything private over that channel.
- geocar 10y ago
  > What's wrong with the QR code? That QR code is a hash of the public key I have no way to verify that. If WhatsApp is trustworthy and secure, then the QR code might be a hash of the public key, but to be completely frank, it could be anything. * I don't have the source code. * Nobody I know has the source code * Nobody I know has bothered to jailbreak their device and/or decompile the binary. I just got an update recently, and my friends are busy. If I had access to my own public and private key, I (or someone I know) could conceivably verify that I'm using it by decrypting my messages using another device (e.g. using wireshark). I appreciate that you might have the source code, or know someone with the source code, or might have reverse engineered the most recent update and have more confidence than I do, but you cannot transmit that confidence to me by simply insisting that it is the hash of the public key.
  - ultramancool 10y ago
    > If WhatsApp is trustworthy and secure, then the QR code might be a hash of the public key, but to be completely frank, it could be anything. Sure, but we're talking about this specific attack's effect on WhatsApp, if you want to debate the relative merits of open source vs closed source End-To-End encryption tools, you may have a point, but it's not one that's relevant here as it has nothing to do with this attack. Unless the attack can be used to update the app or something with a modified malicious version. Say it were Signal instead of WhatsApp if you must. Is there any effect made by this attack?
    - geocar 10y ago
      > Say it were Signal instead of WhatsApp if you must. Is there any effect made by this attack? This is what's known as a false dichotomy. Both systems are as implemented not secure from this attack for the reason I just said.
  - moxie 10y ago
    The source code is for generating the QR code is online here: https://github.com/WhisperSystems/libsignal-protocol-java/blob/master/java/src/main/java/org/whispersystems/libsignal/fingerprint/ScannableFingerprint.java https://github.com/WhisperSystems/libsignal-protocol-java/bl...
    - yownie 10y ago
      thanks moxie.
    - geocar 10y ago
      How do I know that is what is on my device?
  - startling 10y ago
    > If WhatsApp is trustworthy and secure, then the QR code might be a hash of the public key, but to be completely frank, it could be anything. The problem being solved here is validating that another Whatsapp user's key belongs to a flesh-and-blood person you know. We're taking it on faith at this point that Whatsapp's application is trustworthy. If it's not, validating keys is useless -- the app could upload all your chat transcripts in the background for all we know.
moxie 10y ago
Check out the image at the top of the post: https://whispersystems.org/blog/whatsapp-complete/ https://whispersystems.org/blog/whatsapp-complete/

williamscales 10y ago

I think WhatsApp has the big scary warning when keys change disabled by default. You can enable it for yourself but it's buried in the settings.

avar 10y ago
For anyone looking for it: Settings -> Account -> Security -> "Show security notifications = on".
- mtgx 10y ago
  I hope Moxie can share with us why this feature is disabled by default. Does Whatsapp really think the notification would quickly become very annoying for regular users? How often would someone's closest friends really change their phones or uninstall Whatsapp? I imagine not that often for this to be a huge inconvenience, which is why I don't understand why the setting is off by default. Maybe it's something else I'm missing, which is why it would be good for Moxie or Whatsapp to clear up this puzzling choice. Also I hope both the Whatsapp and Signal teams think of ways to encourage security code authentication through better UI. Viber, for instance, has taken an interesting approach to encouraging easier authentication. It probably still doesn't go far enough to make it easy enough for just about anyone to want to authenticate their contacts, but I'd like to see more of this sort of UI experimentation: https://support.viber.com/customer/portal/articles/2017401-viber-security-faq https://support.viber.com/customer/portal/articles/2017401-v...
  - sievebrain 10y ago
    He has said before that key changes in the wild are an extremely common event. I imagine even just the notification that chats are now encrypted caused a lot of confusion and upset given the enormous size of the userbase. Spamming users with warnings that 99.9999% of the time will not be understandable let alone actionable is a quick way to get another SSL warning dialog scenario.
    - feld 10y ago