Encryption was the leitmotif of many events in 2016. The Apple vs FBI standoff brought the privacy to the foreground of the public discussion, and many companies needed to safeguard their positions against the scrutiny. As average users increasingly showed interest in secure means of communication, tech giants could not lose a fraction of their multi-million user base to alternative solutions that based their operations around end-to-end encryption.

Facebook was one of the companies that, following the disturbing events of the Apple case, turned on end-to-end encryption for the millions of its users. The statement by the Facebook went along the lines, “not governments, not even us can read your messages.”

Since WhatsApp implemented Moxie Marlinspike’s code he wrote for Signal, the famous secure messaging app endorsed by Snowden, many in the tech community lauded Facebook for finally “siding with the good.”

The Metadata & Other Issues

Back then, a number of security researchers argued WhatsApp was not as secure as it claimed. Their main argument was that the metadata was not encrypted, and Facebook kept it indefinitely. As Edward Snowden put it:
Another argument against using WhatsApp came from a wide range of privacy activists pinpointing two details:
1) Facebook claimed it would never use WhatsApp to harvest data about its existing Facebook users, and then did just that. It later had to back off due to resonance.
2) Facebook’s business model is based on user profiling, Big Data, and its analytics.
Side note: If you speak German and want to take a sneak peak at how far Big Data analytics can get, read the Das Magazin piece featuring Michal Kosinski, an Assistant Professor in Organizational Behavior at Stanford Graduate School of Business.

In 2014, EFF gave WhatsApp a low privacy score for keeping the encryption keys and not providing forward secrecy.
Nonetheless, the discussion of Facebook’s debatable practices was washed out by the massive applause for the end-to-end encryption feature it finally rolled out to WhatsApp. And the doubters’ voices were once again marginalized and silenced, seeking solace in niche forums.
That is, until last week.

A Backdoor?

Last Friday, The Guardian featured an article “WhatsApp vulnerability allows snooping on encrypted messages.”
A polarizing discussion about WhatsApp backdoor, aka encryption feature, has brought the question back into the spotlight – can you trust WhatsApp?

As of now, the discussion mainly revolves around whether what Tobias Boelter found is a vulnerability, a backdoor, or merely an encryption feature working as expected.
The encryption deployed in WhatsApp relies on the generation of security keys based on Signal protocol. Case in point is WhatsApp can force the generation of new encryption keys for the users who are offline.
“WhatsApp has the ability to force the generation of new encryption keys for offline users, unbeknown to the sender and recipient of the messages, and to make the sender re-encrypt messages with new keys and send them again for any messages that have not been marked as delivered.
The recipient is not made aware of this change in encryption, while the sender is only notified if they have opted-in to encryption warnings in settings, and only after the messages have been resent. This re-encryption and rebroadcasting effectively allows WhatsApp to intercept and read users’ messages.”
It means Facebook could generate keys it would know, or be able to disclose it to a third party (i.e. government, partner) and launch a stealth man-in-the-middle attack. Boelter added MITM attacks can be launched to intercept entire conversations, not just single messages:
“The WhatsApp server can just forward messages without sending the ‘message was received by recipient’ notification (or the double tick), which users might not notice. Using the retransmission vulnerability, the WhatsApp server can then later get a transcript of the whole conversation, not just a single message.”
Boelter reported the issue to Facebook in April 2016, and Facebook replied with a confirmation, “we are aware of the issue, but for now it’s not something we’re actively working on changing.”
Open Whisper Systems endorses Facebook’s approach, as Moxie Marlinspike goes into technicalities of what should be considered as a backdoor, and explaining why the non-blocking is a justified solution in the case when an app has to cater to a billion users.
However, if the lack of transparency is anything to worry about, Facebook lost credibility. We are not talking about the mass users but the entities seeking to protect their confidential communications. There is no way WhatsApp can fit into any organizations data protection plan.

WhatsApp compromised privacy for the sake of usability because enforcing a manual key authentication each time a user’s key changes would disrupt the service for many people quite often. The company’s claim your messages cannot be read by anyone but you and your recipient is simply not true. If it were, WhatsApp would have been positioned as a zero-knowledge platform.
No Good Against Advanced Adversaries

Perhaps, such solution is feasible for an app with a billion users, but is it safe to use for businesses or anyone taking their privacy seriously? Most definitely, not. If the server acts as a trusted man in the middle, can you trust it not to be compromised by resourceful agents? Governments, or hacker conglomerates, active participants of the black market trading on the corporate secrets – can they exploit the way WhatsApp handles key generation to intercept conversations? Yes, they can and WhatsApp makes it easier for them.

Tobias Boelter made a sharp remark that wraps up the gist of the debate:
“[WhatsApp is] A very good messenger for the masses, but not one that can protect against advanced adversaries.”
Backdoor, Or Not, It’s Not Private
Call it a backdoor, or a deliberately designed feature, you would not want to send your financial information or merger plans via WhatsApp. Facebook is a compromised brand as far as privacy is concerned. It is these privacy-related concerns that make zero-knowledge providers a rising trend in the communications sector.

As companies are looking to a) protect their communications from hackers, entities engaging in business espionage; b) ensure compliance with emerging privacy-protecting laws (i.e. GDPR in EU, HIPAA in the U.S.); c) ensure their provider can not disclose their data to law enforcement or a competitor; they are increasingly turning to providers operating on the zero-knowledge principle and located in the countries with strong privacy-protecting laws.


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