Moxie Marlinspike, the co-founder and chief executive of encrypted-messaging app Signal, has resigned.
He blogged it was a “good time to replace myself as CEO” after working on Signal for over a decade.
Some users were concerned when Signal recently enabled crypto-currency payments within the app.
Mr Marlinspike will continue to serve on the Signal Foundation’s board of directors, while Brian Acton, the board’s executive chair, will serve as interim CEO.
Mr Marlinspike, real name Matthew Rosenfeld, blogged that he had always hoped for Signal to “grow and sustain” beyond his involvement.
“I was writing all of the Android code, all of the server code, was the only person on call for the service, facilitated all product development, and managed everyone,” he wrote.
“I couldn’t ever leave cell service, had to carry my laptop with me everywhere in case of emergencies, and occasionally found myself sitting alone on a rainy sidewalk late at night trying to diagnose a service degradation.”
Signal is now used by over 40 million people.
It is free, and messages are automatically encrypted by default, just like WhatsApp.
Mr Marlinspike’s skills as a programmer and cryptographer have benefited both Signal and WhatsApp.
The Signal Protocol, which he created, has also been integrated into WhatsApp, as well as several other popular instant-messaging apps.
While Mr. Marlinspike’s tenure as CEO has seen Signal grow in popularity, a recent experiment with cryptocurrency has caused some users concern.
In November, the app made available to all users a trial of an integrated payment system based on MobileCoin, a crypto-currency that claims to be both highly secure and environmentally friendly.
Mr Marlinspike has reportedly provided technical advice to the crypto-currency start-up.
Integrating a crypto-currency is, some say, a risky strategy, creating avenues for criminal misuse of the app and putting it within scope of financial legislation – such as anti-money-laundering laws – and regulation.
Alex Stamos, formerly Facebook’s chief security officer, told The Verge: “The addition of pseudo-anonymous money-transfer functions greatly increases their legal attack surface, while creating the possibility of real-life harms.”
Mr Marlinspike’s replacement, Mr Acton, is also a veteran of the secure-messaging sector.
Mr Acton left WhatsApp, which he co-founded, in 2017 – the messaging app had been sold to Facebook, in 2014, in a deal worth $19bn (£11.4bn) in cash and shares.
He cites ” differences surrounding the use of customer data and targeted advertising” as reasons for his departure from WhatsApp.
And, in 2018, with Mr Marlinspike, he launched the Signal Foundation, providing funding of $50m.