Open Whisper Systems on Tuesday announced a partnership with Facebook-owned WhatsApp to use TextSecure protocol to essentially scramble messages in transit, hiding whatever is inside from prying eyes.
"WhatsApp deserves enormous praise for devoting considerable time and effort to this project," Open Whisper Systems said in a blog post.
"Even though we're still at the beginning of the rollout, we believe this already represents the largest deployment of end-to-end encrypted communication in history."
WhatsApp confirmed the announcement to AFP but declined to comment further.
TextSecure encryption enabled automatically as a default setting is already built into most recent version of WhatsApp for mobile devices powered by Google-backed Android software, with billions of messages being exchanged daily, according to Open Whisper.
"(WhatsApp co-founder) Brian Acton and the WhatsApp engineering team has been amazing to work with," Open Whisper said.
"Their devotion to the project as well as their thoroughness in getting this done are inspiring in a world where so many other companies are focused on surveillance instead of privacy."
Open Whisper is an open-source project supported by donations and grants.
While taking part in a South By Southwest conference earlier this year, former National Security Agency contractor Snowden praised encryption tools offered by Open Whisper.
Snowden connected to the gathering remotely from Russia, where he took refuge after leaking information about wide-scale online surveillance by the NSA.
Facebook in October completed its buy of mobile messaging application WhatsApp, with the mostly stock deal tallying nearly $22 billion.
Facebook, the world's biggest social network, announced the buyout of the WhatsApp messenger service, used by 600 million people, in February and US authorities approved the deal in April.