Just how secure is end-to-end encrypted messaging?

Facebook-owned application WhatsApp introduced end-to-end encrypted messaging last year, and while it was received well by the general public, security implications have made it a difficult ride for the company. In January, a report revealed vulnerabilities in the messaging service that could allow Facebook and others to intercept and read WhatsApp messages. Experts are now calling into question the security of encrypted messaging services.

WhatsApp introduced full encryption for its services in March 2016 as a means of ensuring that only the sender and the receiver could view messages being sent via the app. The new privacy feature applied to everything that is uploaded within a WhatsApp chat, including photos, videos and group messages. WhatsApp says end-to-end encryption prevents content and calls from “falling into the wrong hands.”

"Every day we see stories about sensitive records being improperly accessed or stolen," the company said in a blog post at the time. "And if nothing is done, more of people's digital information and communication will be vulnerable to attack in the years to come. Fortunately, end-to-end encryption protects us from these vulnerabilities.”

Written in WhatsApp’s ‘Security’ section on the app it reads: “Many messaging apps only encrypt messages between you and them, but WhatsApp’s end-to-end encryption ensures only you and the person you’re communicating with can read what is sent and nobody in between, not even WhatsApp. This is because your messages are secured with a lock, and only the recipient and you have the special key needed to unlock and read them.”

That all sounded great until security researcher Tobias Boelter discovered a WhatsApp security loophole which he reported to Facebook in April 2016. Boelter discovered a vulnerability that could potentially allow the company to read messages sent via WhatsApp and also provide government agencies a “backdoor” to access messages of people who believe their messages to be secure. Facebook said it was aware of the issue and that it wasn’t pursuing a solution because it was “expected behavior”.

The loophole has been described by security experts as an acceptable “tradeoff” that allows WhatsApp to be easy to use on a daily basis. The risk to majority of users is said to be “remote” since the vulnerability only allows for targeted surveillance of individuals or groups of individuals at specific times, as opposed to a large scale mass surveillance of WhatsApp users worldwide.

The vulnerability centers on the generation of unique security keys in WhatsApp’s end-to-end encryption, using the acclaimed Signal Protocol, developed by software organization Open Whisper Systems which maintains an encrypted communications application called Signal. These security keys are traded and verified between users to guarantee communications are secure and cannot be intercepted by someone in the middle. However, Boelter discovered it’s not that simple…

WhatsApp, he claims, is able to force the generation of new encryption keys for offline users, which the user and sender of the message would be unaware of, and make the sender re-encrypt messages with new keys and send them again for any messages that have not been flagged as delivered.

This change in encryption is unknown to the recipient, and the message sender is only made aware if they have opted-in to encryption warning in WhatsApp settings, but this is only after the message has been delivered. This process of re-encrypting and re-broadcasting previously undelivered messages could potentially allow WhatsApp to intercept and download messages that were intended to be sent privately.

“If WhatsApp is asked by a government agency to disclose its messaging records, it can effectively grant access due to the change in keys,” says Boelter.

The vulnerability is not necessarily an issue related to the Signal Protocol, because Open Whisper Systems’ messaging app, Signal, does not share the vulnerability. If a message recipient using Signal changes the security key while offline, for example, the sent message will not be delivered and the sender will receive notification of the change in security keys without the message being automatically sent. This differs to WhatsApp, which automatically resends an undelivered message with a new key without warning the user.

The loophole has been verified by other security experts, such as Steffen Tor Jensen, head of information security and digital counter-surveillance at the European-Bahraini Organization for Human Rights, who says, “WhatsApp can effectively continue flipping the security keys when devices are offline and re-sending the message, without letting users know of the change till after it has been made, providing an extremely insecure platform.”

WhatsApp responded in a statement insisting it “does not give governments a ‘backdoor’ into its system and would fight any government request to create a backdoor.” The controversy adds to a growing list of privacy issues for WhatsApp ever since it was acquired by Facebook in 2014 for $22 billion.

After the recent March 22 Westminster attack in London, the British Government said it wants its security services to have access to all encrypted messaging applications such as WhatsApp, as it was revealed that the app was used by the attacker to send an encrypted message before the incident.

Home Secretary Amber Rudd told Sky News it was “completely unacceptable” that the police and security services were not able to access the encrypted WhatsApp service to see the message that was sent by the attacker. Rudd said: “You can’t have a situation where you have terrorists talking to each other – where this terrorist sent a WhatsApp message – and it can’t be accessed.”

The UK recently passed the Investigatory Powers Act which allows the government to intercept bulk data of users held by private companies, even without suspicion of criminal activity. According to a Guardian report, private companies can be forced to “maintain technical capabilities” that facilitate data collection through hacking and interception. Companies can also be made to remove “electronic protection” from data.

Some experts suggest WhatsApp’s exposed vulnerability could be a “gold mine for security agencies” and facilitate government interception of private citizens. Professor Kirstie Ball, co-director and founder of the Centre for Research into Information, Surveillance and Privacy, says: “It’s a huge threat to freedom of speech, for it to be able to look at what you’re saying if it wants to.”

WhatsApp first came under fire for security reasons in August last year after updating its terms-of-service to begin sharing user phone numbers, profile data, status message and online status with Facebook for advertising purposes.

The Electronic Privacy Information Centre (EPIC) accused WhatsApp of breaking its promise to users after announcing in 2014 that its sale to Facebook would not affect its privacy policy, and that it would never share or sell “personally identifiable information” such as phone numbers, name and profile data.

WhatsApp defended itself from the accusations, referring to an option for users to opt-out of the sharing portion of the terms-of-service. But that didn’t protect WhatsApp and Facebook from a Federal Trade Commission consent order, claimed EPIC, which requires companies to offer ‘opt-in’ consent to users before asking them to agree to new terms.

WhatsApp provided an opt-in option in a way, but it wasn’t clear enough how to access it. For instance, a user had to click “read” to view the terms-of-service agreement before the opt-in checkbox appears on screen.

Facebook and WhatsApp subsequently ended the sharing of user data in November last year after pressure from the European Union’s independent data protection authority Article 29 Working Party in October. The European Commission filed charges against Facebook for providing “misleading” information during the period before it acquired WhatsApp, following its data sharing change.