WhatsApp is bracing itself for a clash with the US government over encryption. In an interview with The Wall Street Journal published Wednesday, the head of WhatsApp, Will Cathcart, said the messaging app had hit 2 billion users, up from 1.5 billion two years ago. It still falls behind the core Facebook app, which has 2.5 billion users. Cathcart used the interview as a chance to draw a line in the sand over end-to-end encryption, the system that allows WhatsApp users’ messages to stay private and inaccessible even by WhatsApp. WhatsApp and its parent company, Facebook, have come under pressure from the US government recently to create ways for law enforcement to circumvent encryption. Attorney General William Barr last year asked Facebook to delay its plans for encrypting all its messaging platforms — which Facebook rejected. “For all of human history, people have been able to communicate privately with each other,” Cathcart told The Journal, adding: “And we don’t think that should go away in a modern society.” The US isn’t the only government that’s been pressuring WhatsApp to break encryption. Last year the allied “Five Eyes” intelligence-sharing countries (the US, the UK, Canada, Australia, and New Zealand) united in pushing for encrypted services to build “safeguards” for law enforcement — though they stopped short of calling for deliberate security vulnerabilities known as backdoors. The argument against backdoors runs that they weaken the system, as they could be exploited by malicious actors rather than law enforcement. Cathcart said that despite Facebook CEO Mark Zuckerberg’s grand plans to weave together Facebook’s suite of social-media platforms including Instagram and WhatsApp, WhatsApp’s engineers were still focused on a constrained set of products consisting of private messaging, payments, and customer-service tools for businesses.