The encryption-system behind signal was developed by Matthew Rosenfield, aka, Moxie Marlinspike. He founded "Whisper Systems", which was purchased by Twitter. After that, Rosenfield left and founded "Open Whisper Systems" - which later renamed itself "Signal". Jack has been promoting Signal - indicating that Jack Dorsey and Matthew Rosenfield continue to be closely connected. To reiterate, Rosenfield *founded* Signal. He remains *at Signal*. (Another co-founder of signal: Brian Acton, who had come to Rosenfield from *Facebook*.)