Last month, Meta began rolling out default end-to-end encryption to Messenger, its one-billion-plus-member messaging platform spun off from Facebook. The long-standing app has incorporated end-to-end encryption as an option since 2016, but over the course of 2024, all of Messenger’s billion-plus users will see the option enabled by default for their person-to-person messages.
Meta’s move is no paradigm shift: In addition to Messenger’s existing encryption option, Meta-owned WhatsApp and its 2 billion users have had default end-to-end encryption since 2016, on top of non-Meta apps like Signal that already employ the technology. But even analysts and privacy advocates who question Meta’s historical record on privacy view the move as a step forward. “I think that this is a rare situation where [Meta] has done something that I completely agree with, that I think is wholly a net positive for the world,” says Cooper Quintin, a researcher with the Electronic Frontier Foundation.
“I think it’s great to see Facebook putting some of their massive resources into making it clear that end-to-end encryption is important for everybody.”
—Cooper Quintin, Electronic Frontier Foundation
Still, unanswered questions remain. For one, although there is little reason to doubt the security of Messenger’s protocol, Meta has not opened it for outside cryptographers to verify. For another, while Meta won’t collect messages themselves, there is nothing stopping them from collecting metadata on those very messages.
Following Signal’s lead
Even under the hood, Messenger is following in the fashion of its fellow messaging apps. To encrypt messages, Messenger uses an implementation of the Signal protocol, an open-source encryption method initially created for the app of the same name. WhatsApp uses the same protocol, as do Skype and Android Messages.
Cryptographers have tried and tested the Signal protocol and generally rate it highly. “It’s what everybody does, for good reason,” says Martin Albrecht, professor of cybersecurity at King’s College London. “It’s a good protocol.”
Where Messenger differs from its competitors, even WhatsApp, is in how the app stores and backs up encrypted messages. The app employs a Meta-created protocol, Labyrinth, for the task.
“This also demonstrates how much can be inferred from behaviors and metadata without needing access to the actual contents of messages themselves.”
—Ed Geraghty, Privacy International
Ideally, Albrecht says, Meta would let independent cryptographers conduct their own verification of Messenger’s encryption. Cryptographers could implement the protocol, determine whether it matches Meta’s specification, and walk away with either a proof of the protocol’s security or a potential attack.
“I don’t think [Meta] will do this—they haven’t done this for WhatsApp,” Albrecht says. “This doesn’t mean that it’s necessarily a problem. It’s just that, if you want to actually have some assurances, that would be the standard to aspire to.”
Meta has a reputation for collecting its users’ data: a key part of its lucrative advertising business. In fact, last year, the company earned a US $1.3 billion fine from European Union regulators for transferring EU citizens’ Facebook data to the United States. Despite this reputation, at least in its communications, Meta prides itself on offering messaging that is encrypted to prevent the authorities from reading its users’ messages. (Meta, however, did not respond to IEEESpectrum‘s requests for comment.)
U.K. controversy simmers, roils
As Meta began rolling end-to-end encryption out to Messenger, the company found itself on the defensive from some of those authorities. A global task force of law-enforcement agencies from every continent criticized the rollout as dangerous. Perhaps no critic has been as vocal as the U.K. government; a litany of government figures have blasted the rollout plan both before and after it began. The usual claim is that end-to-end encryption would facilitate the spread of child sexual abuse material.
In this dispute, privacy advocates are generally taking Meta’s side. “I don’t buy the U.K.’s argument, and I think it’s great to see Facebook putting some of their massive resources into making it clear that end-to-end encryption is important for everybody,” says Quintin.
Even if end-to-end encryption was an option, many Messenger users may not have had the technological or security awareness to know the option’s significance.
At first, Messenger will encrypt one-on-one direct messages and phone calls. In the future, this will eventually extend to Messenger groups. Meta has also announced plans to encrypt messages on Instagram, another app it owns.
“Given Meta’s position in the advertising sector, removing server-side processing of messages’ content is undoubtedly a net positive,” says Ed Geraghty, senior technologist at London-based advocacy group Privacy International.
There is a possible catch. Meta’s documentation indicates the company will continue to process messages’ metadata: what time a message was sent, for example, and who sent it to whom. The company says it will use metadata to help identify bad actors. Privacy advocates see this use case as evidence metadata can make a double-edged sword.
“This also demonstrates how much can be inferred from behaviors and metadata without needing access to the actual contents of messages themselves,” says Geraghty. “So we have to ask: What could Meta be using this data for additionally? It’s likely this metadata will be used to continuously enrich user profiles for targeted advertising purposes.”