WhatsApp, the Facebook-owned free messaging app, is in the middle of a controversy over whether there’s an intentional backdoor in its encryption that poses a “huge threat to freedom of speech.”
WhatsApp has issued a statement saying that this characterization is patently false.
Cryptography researcher Tobias Boelter told the Guardian that WhatsApp is able to remotely change the unique encryption keys for user accounts—something that WhatsApp doesn’t deny. Boelter went on to say that this leaves unsent messages open to man-in-the-middle attacks.
Essentially, in the background, unique security keys are traded and verified between WhatsApp users to guarantee communications are secure and cannot be intercepted by a middleman. However, WhatsApp has the ability to require 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 article cited privacy concerns that the situation could be exploited by law enforcement or governments to track and “listen” to conversations.
“[Some] might say that this vulnerability could only be abused to snoop on ‘single’ targeted messages, not entire conversations,” Boelter told the Guardian, adding that he made Facebook aware of the issue back in April 2016. “This is not true if you consider that 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.”
WhatsApp however said in a statement to media that all of this is hyperbole; and that it simply gives itself the ability to change the keys so that it can ensure seamless message service if a user changes SIM cards or devices:
"The Guardian posted a story this morning claiming that an intentional design decision in WhatsApp that prevents people from losing millions of messages is a 'backdoor' allowing governments to force WhatsApp to decrypt message streams. This claim is false. WhatsApp does not give governments a 'backdoor' into its systems and would fight any government request to create a backdoor. The design decision referenced in the Guardian story prevents millions of messages from being lost, and WhatsApp offers people security notifications to alert them to potential security risks."
For instance, one option in the account security controls allows users to be notified when a security key has been changed.
In the original article, it also had this to say:
"This is because in many parts of the world, people frequently change devices and SIM cards. In these situations, we want to make sure people's messages are delivered, not lost in transit."
However, some say that this can pose a security risk despite WhatsApp’s statement to the contrary—albeit a tough one to pull off. Alec Muffett, a former Facebook engineer, told Gizmodo: ""[If] I am sending to you, and your phone is offline because your [battery] is flat, or you have no coverage, or something. Some messages 'back up' on my phone, waiting to talk to yours….The proposition is that this condition [means that] backed-up messages, combined with someone colluding with Facebook, [can allow] WhatsApp to 'fake' the 'person has a new phone' condition, can lead to the backed-up messages being re-encrypted and sent to the new, fake or colluded phone."
However, he agreed that characterizing this as a backdoor was “ridiculous” and “ignoble”—and is, in fact, simply a usability issue with encryption in general.
Several security researchers have taken to Twitter to discuss, and while most agree that the accusation of there being a “backdoor” is too much, the situation still reflects poor design decisions on the part of WhatsApp:
“Non blocking is ok but at the very friggin least the warning ought to have been enabled by default. That sucks a lot,” one commentator tweeted.