Good news for people who love privacy and security, bad news for black-hat hackers and government surveillance agencies. WhatsApp, the wildly popular messaging app, has partnered with the crypto gurus at Open WhisperSystems to implement strong end-to-end encryption on all WhatsApp text messages–meaning not even Zuck himself can pry into your conversations, even if a court order demands it1.

WhatsApp, of course, has hundreds of millions of daily users worldwide, and was purchased by Facebook earlier this year for an eye-popping $19 billion. Open WhisperSystems creates state-of-the-art end-to-end encryption systems such as Signal, for voice, and TextSecure, for text. (They have nothing to do with the messaging app Whisper.) As per the EFF’s Secure Messaging Scorecard, TextSecure is a huge upgrade from WhatsApp’s previous encryption.

And I do mean huge. Right now the TextSecure protocol has only rolled out to WhatsApp for Android–other clients, and group/media messaging, are coming soon–but already “billions of encrypted messages are being exchanged daily … we believe this already represents the largest deployment of end-to-end encrypted communication in history,” to quote OWS founder Moxie Marlinspike.

This comes in the wake of Apple, similarly, encrypting iOS 8 devices such that Apple cannot retrieve data stored on them (albeit in a closed-source, unverifiable way.) FBI director James Comey subsequently claimed “the post-Snowden pendulum” has “gone too far” amid concerns that the world is “going dark” to wiretaps and surveillance. They and other three-letter agencies–along with black-hat hackers and governments worldwide, thanks to WhatsApp’s immense global reach–won’t be happy about their new inability to pry into the contents of WhatsApp text messages.

However, Comey’s claims appear to suffer from the slight disadvantage of being false:

A reminder that when the FBI tells you it's "going dark" and it needs more surveillance powers, they are lying: http://t.co/z6o87owzee — Eva (@evacide) November 17, 2014

and I think the tech industry’s response to the FBI and NSA’s dismay at the widespread use of end-to-end encryption by more and more companies, and the notion that the tech industry is “picking a fight” with them, can be summed up as:

If Silicon Valley firms tapped NSA data centers, backdoored NSA crypto, and sent NSA malware, *then* they would have been "picking a fight." — Declan McCullagh (@declanm) November 5, 2014

And it’s fair to say that, in a world where surveillance technology seems to grow more powerful and pervasive every week, any meaningful blow that can be struck for privacy and anonymity is a welcome rebalancing. Kudos to WhatsApp for making this happen–Marlinspike, who approached them with the idea, stresses how impressed he’s been by their eagerness, dedication, and thoroughness–and to Open WhisperSystems for making it possible.

Marlinspike says OWS’s own goal is to keep producing strong, open-source privacy and security tools that companies (and individuals) can easily incorporate into their own services, without having to do their own crypto research and/or protocol design. They’ll keep working on Signal and TextSecure as reference implementations, using them to push the envelope and prove new ideas; and in the meantime, in one fell swoop, their TextSecure protocol suddenly has hundreds of millions of daily users, more than all but a tiny handful of companies.

1eta: well, sort of, by which I mean, not really. As an expert friend points out, there are many ways other than server-side tapping / man-in-the-middle attacks to skin this particular cat; app backdoors, device keystroke loggers, etc.