Is There A Truly Secure Messaging App?
One could spend hours examining all the encrypted communications tools available, from popular services such as WhatsApp and Facebook’s Messenger to newcomers such as Signal and Wire. That point was driven home recently with the revelation that attackers could exploit a security vulnerability in WhatsApp to snoop on its users.
The vulnerability was found in the service’s implementation of end-to-end encryption, which is supposed to make it all but impossible for messages to be read by anyone except their intended recipient, and in WhatsApp’s management of the unique security keys used to scramble and unscramble those messages on users’ devices.
The problem stemmed from WhatsApp’s ability to create new encryption keys for offline users. This is common for secure communication tools, but WhatsApp is set apart by its decision to re-encrypt messages with the new keys without informing their sender or recipient.
This could allow someone to intercept communications with no indication to anyone involved with the conversation. WhatsApp has therefore effectively undermined the basic principle of end-to-end encryption.
It would be easy to overreact to this issue. WhatsApp did not create a backdoor into its service – a claim with which Brian Acton, the company’s co-founder, has taken issue with, saying WhatsApp would “fight any government request” to create one.
Nor did it introduce a vulnerability so critical that people should remove the app from their devices. Concerned users can verify someone’s identity by comparing the “fingerprints” associated with their key, and they can enable a setting that notifies them when a message has been re-encrypted with a new key.
Yet even the nature of those notifications is up to question. There are two options, blocking or non-blocking, which refer to requiring users to manually verify that a new key is legitimate or simply notifying them when a key has been changed. WhatsApp notifications are non-blocking. Signal, the encrypted messaging tool from Open Whisper Systems (OWS) whose end-to-end encryption protocol is used in WhatsApp, Messenger and other apps, uses blocking notifications.
Moxie Marlinspike of OWS said Signal planned to make blocking notifications an option for some users and use non-blocking notifications by default.
“The feedback we’ve gotten is that most of our users don’t want these messages to be blocking,” he said. “What they want is just to have the ability to verify the integrity of their communication and to see when these things are happening, but they don’t want it to interrupt their ordinary workflow.”
Which brings the conversation back to the root of the problem: should messaging apps
“It really depends on the service provider and the risk it wants to take,” said Alan Duric, chief technology officer at the Wire secure communications provider.
“It is relatively difficult for WhatsApp to put it as ‘blocking’ when it has a billion users. And by doing it [the way WhatsApp has done it] you have a trade-off with the user experience and sacrificing something on security.”
Wire takes the opposite approach by valuing security over convenience.
Some messaging apps follow WhatsApp in not informing users of key changes by default. Others, like Wire, don’t send messages to people with new keys without user consent. These companies will face criticism no matter what they choose. WhatsApp users might worry that their messages are insecure; Wire users might grow tired of security notifications, and might change their approach based on user feedback as OWS is doing with the Signal app.
There is no right or wrong answer. The same can be said for other decisions, such as Google’s Allo and Facebook Messenger’s “secret conversations” not using end-to-end encryption by default, which the companies say allows them to offer features that wouldn’t be possible otherwise. Apps that do use encryption by default – such as Signal and Wire, among others – require people to convince everyone with whom they wish to communicate to switch to unfamiliar messaging tools.
Which is why these companies have different approaches to the same problem. WhatsApp has to decide between making 1 billion people more secure in non-obtrusive ways or notifying them every time a security key has changed. Google must balance efforts to make people more secure with the desire to offer features that could help a newcomer like Allo compete with established services. Even more privacy conscious apps like Signal have to design with their users in mind.
There will never be a one-size-fits-all in the secure communications market. Just as these services have to decide on what problems they wish to solve, consumers must choose the app that best suits their needs. More apps support end-to-end encryption than ever, and even if none of them are perfect, this means private communications are more secure than before. These are nuanced problems that must be considered with care instead of being oversimplified.
“WhatsApp has designed a pretty good thing with really considerable care and has successfully deployed it to the largest network of end-to-end encryption in the history of the world,” Marlinspike said.
“Approaching questions of the best user experience and how we should think about these problems by just calling this a ‘backdoor’ and telling everyone to uninstall WhatsApp does a lot more harm than good, because it’s just going to drive people to other apps that use way less consideration and care that users are also not capable of evaluating the goodness of.”
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