A discovered vulnerability in the WhatsApp messaging service, which could allow encrypted messages to be read, has been described as normal behavior by WhatsApp. This vulnerability is a “man in the middle” attack and requires server access. Following the initial news, WhatsApp responded by explaining that this was not a vulnerability but a backdoor and that the company has designed the messaging service this way. Facebook, WhatsApp’s owners, had previously explained that the WhatsApp messaging service was encrypted and that no-one could intercept messages, keeping things secure for its billion plus users. The services uses the Signal protocol, whereby users essentially swap and verify unique security keys, used to ensure a secure connection. However, the WhatsApp service has the ability to generate new encryption keys for offline users without the knowledge of either side of the conversation. This would cause the sender to re-encrypt undelivered messages with new keys, and these messages could be read by an attacker. Furthermore, existing messages could also be retransmitted by the server, meaning the entire conversation could be read. The sender would be notified if they have opted in to encryption warnings on the application, but only after the messages have been resent and the new encryption key used.
Although WhatsApp uses the Signal protocol, shared with the Signal application, the protocol is not the source of the vulnerability but merely how it is implemented. When using Signal and these circumstances happen, the message is not re-sent and instead the sender is notified. The security vulnerability was discovered by a security researcher at the University of California, Berkeley, Tobias Boelter, who reported the vulnerability to Facebook back in April 2016. At the time the company explained they were aware of the issue and that it was “expected behavior.” The company had no plans to work on the issue and British newspaper, the Guardian, has verified that the loophole exists today. The vulnerability requires the hacker to have access to a server or be “unusually skilled,” and so is considered to be beyond the reach of most criminals – but not a court order. Furthermore, should a government agency intercept messages using the WhatsApp server, notifications would be sent to anybody with the notification service enabled on their devices. This would be extremely obvious and visible to all WhatsApp users, arguably more obvious than a update to the application removing end to end encryption.
WhatsApp is used by customers all over the world including in oppressive regimes. The WhatsApp vulnerability has already been described by Professor Kirstie Ball, founder of the Centre for Research into Information, Surveillance and Privacy, as both “a gold mine for security agencies” and “a huge betrayal of user trust… It is a huge threat to freedom of speech, for it to be able to look at what you’re saying if it wants to.” The issue has raised the question that this type of server attack could be used by companies or government agencies. The source article explains that WhatsApp has become “a go to communications tool of activists, dissidents and diplomats.”
However, whilst privacy groups are expressing how unhappy they are with the WhatsApp service, unfortunately there are already legal frameworks in place around the world that encourage or require companies to retain at least the ability to allow access to information. In the case of the United Kingdom, the Investigatory Powers Act permits significant data to be intercepted by the even without the suspicion of criminal activity. Furthermore, the government have the ability to require businesses maintain the ability to intercept user data and to remove “electronic protection.” The WhatsApp vulnerability may have been designed with this legal framework in mind.
WhatsApp, talking to the Guardian newspaper, explained that the service is “simple, fast, reliable and secure.” The spokesperson explained that in 2016 the company enabled encryption by default but that they “focus on keeping the product simple and take into consideration how it’s used every day around the world.” One of the reasons for allowing the retransmission vulnerability is if customers change their handset or reinstall the application and the company wanted “to make sure people’s messages are delivered, not lost in transit.” The spokesperson would not directly answer if WhatsApp had already accessed messages at the request of a third party or government agency but instead advised to visit the website page showing aggregated government data requests by country. Essentially, WhatsApp are using a lesser level of security so that users who change SIM cards or handsets do not lose their messages and contacts. Although WhatsApp differs from Signal, the company takes the view that its user base is different to Signal, where security is less critical than ease of use.
Although the WhatsApp vulnerability would be difficult to use without notifying the target, it still exists. WhatsApp, and parent Facebook, could be trying to negotiate between keeping customer data secure and complying with the law. For the user wishing the best security, Signal is the messaging service that Edward Snowden recommends and the WhatsApp story does not change this. Going forwards, the industry is working towards making the encryption process more visible to customers under the “key transparency” solution: Google is already building a key transparency system, but the question within the industry is still how is encryption technology made visible without being confusing?