Facebook claims that no one can intercept WhatsApp messages, not even the company and its staff, ensuring privacy for its billion-plus users. But new research shows that the company could in fact read messages due to the way WhatsApp has implemented its end-to-end encryption protocol.
The security loophole was discovered by Tobias Boelter, a cryptography and security researcher at the University of California, Berkeley. He told the Guardian: “If WhatsApp is asked by a government agency to disclose its messaging records, it can effectively grant access due to the change in keys.”
The vulnerability is not inherent to the Signal protocol. Open Whisper Systems’ messaging app, Signal, the app used and recommended by whistleblower Edward Snowden, does not suffer from the same vulnerability. If a recipient changes the security key while offline, for instance, a sent message will fail to be delivered and the sender will be notified of the change in security keys without automatically resending the message.
Comments from Open Whisper Systems :
Today, the Guardian published a story falsely claiming that WhatsApp’s end to end encryption contains a “backdoor.”
WhatsApp’s encryption uses Signal Protocol, as detailed in their technical whitepaper. In systems that deploy Signal Protocol, each client is cryptographically identified by a key pair composed of a public key and a private key. The public key is advertised publicly, through the server, while the private key remains private on the user’s device.
This identity key pair is bound into the encrypted channel that’s established between two parties when they exchange messages, and is exposed through the “safety number” (aka “security code” in WhatsApp) that participants can check to verify the privacy of their communication.
One fact of life in real world cryptography is that these keys will change under normal circumstances. Every time someone gets a new device, or even just reinstalls the app, their identity key pair will change. This is something any public key cryptography system has to deal with. WhatsApp gives users the option to be notified when those changes occur.
It is great that the Guardian thinks privacy is something their readers should be concerned about. However, running a story like this without taking the time to carefully evaluate claims of a “backdoor” will ultimately only hurt their readers. It has the potential to drive them away from a well engineered and carefully considered system to much more dangerous products that make truly false claims. Since the story has been published, we have repeatedly reached out to the author and the editors at the Guardian, but have received no response.