Even for Signal, engineering privacy is fraught with pitfalls

Signal has become the privacy-focused consumer’s go-to messaging app. But a recent change to its back-end systems, designed to make the app more accessible and competitive with other encrypted-messaging services, could be putting user data at risk.

At the core of Signal’s appeal is a level of digital protection and commercial disinterest in its users’ communications rarely seen by messaging-service providers. Signal is now used broadly, not just by hackers and professional paranoids, but also by activists, journalists, politicians, and any number of people who believe that their text messages and phone calls should be as private as an in-person conversation. Few other apps offer a similar level of security and privacy.

While privacy is central to Signal, it is not immune to security challenges. In May, the company released a new PIN-based system that would have allowed users to back up their contact lists—and eventually their messages—to the cloud. The new feature was built on a system with known security flaws, as many ardent Signal users angrily pointed out on Twitter in the ensuing weeks.

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Signal’s recent stumble stemmed from its attempts to be different from other messaging services, even those with relatively good privacy features, such as Facebook’s WhatsApp or Apple’s iMessage. Most messaging services use encryption to protect messages from being spied on when in transit between sender and recipient. But even services that encrypt messages usually store them—along with the user’s address book—in plaintext, unencrypted.

Building contact and message backups—something that all of Signal’s primary competitors offer—into a system whose primary feature is that all communications are encrypted end to end is a difficult task to accomplish in modern computing.

This story was originally commissioned by Fast Company. Read the full story here.