The security researcher cited in the report acknowledged that the word ‘backdoor’ was probably not the best choice.
WhatsApp this week denied that its app provides a “backdoor” to encrypted texts.
A report published Friday by The Guardian, citing cryptography and security researcher Tobias Boelter, suggests a security vulnerability within WhatsApp could be used by government agencies as a backdoor to snoop on users.
“This claim is false,” a WhatsApp spokesman told PCMag in an email.
The Facebook-owned company will “fight any government request to create a backdoor,” he added.
WhatsApp in April turned on full end-to-end encryption—using the Signal protocol developed by Open Whisper Systems—to protect messages from the prying eyes of cybercriminals, hackers, “oppressive regimes,” and even Facebook itself.
The system, as described by The Guardian, relies on unique security keys traded and verified between users in an effort to guarantee communications are secure and cannot be intercepted. When any of WhatsApp’s billion users get a new phone or reinstall the program, their encryption keys change—”something any public key cryptography system has to deal with,” Open Whisper Systems founder Moxie Marlinspike wrote in a Friday blog post.
During that process, messages may back up on the phone, waiting their turn to be re-encrypted.
According to The Guardian, that’s when someone could sneak in, fake having a new phone, and hijack the texts.
But according to Marlinspike, “the fact that WhatsApp handles key changes is not a ‘backdoor,’ it is how cryptography works.
“Any attempt to intercept messages in transmit by the server is detectable by the sender, just like with Signal, PGP, or any other end-to-end encrypted communication system,” he wrote.
“We appreciate the interest people have in the security of their messages and calls on WhatsApp,” co-founder Brian Acton wrote in a Friday Reddit post. “We will continue to set the record straight in the face of baseless accusations about ‘backdoors’ and help people understand how we’ve built WhatsApp with critical security features at such a large scale.
“Most importantly,” he added, “we’ll continue investing in technology and building simple features that help protect the privacy and security of messages and calls on WhatsApp.”
In a blog post, Boelter said The Guardian’s decision to use the word “backdoor” was probably not “the best choice there, but I can also see that there are arguments for calling it a ‘backdoor.'” But Facebook was “furious and issued a blank denial, [which] polarized sides.
“I wish I could have had this debate with the Facebook Security Team in…private, without the public listening and judging our opinions, agreeing on a solution and giving a joint statement at the end,” Boelter continued.
In an earlier post, Boelter said he reported the vulnerability in April 2016, but Facebook failed to fix it.
Boelter—a German computer scientist, entrepreneur, and PhD student at UC Berkeley focusing on Security and Cryptography—acknowledged that resolving the issue in public is a double-edged sword.
“The ordinary people following the news and reading headlines do not understand or do not bother to understand the details and nuances we are discussing now. Leaving them with wrong impressions leading to wrong and dangerous decisions: If they think WhatsApp is ‘backdoored’ and insecure, they will start using other means of communication. Likely much more insecure ones,” he wrote. “The truth is that most other messengers who claim to have “end-to-end encryption” have the same vulnerability or have other flaws. On the other hand, if they now think all claims about a backdoor were wrong, high-risk users might continue trusting WhatsApp with their most sensitive information.”
Boelter said he’d be content to leave the app as is if WhatsApp can prove that “1) too many messages get [sent] to old keys, don’t get delivered, and need to be [re-sent] later and 2) it would be too dangerous to make blocking an option (moxie and I had a discussion on this).”
Then, “I could actually live with the current implementation, except for voice calls of course,” provided WhatsApp is transparent about the issue, like adding a notice about key change notifications being delayed.