[7] Marlinspike is a former head of the security team at Twitter[8] and the author of a proposed SSL authentication system replacement called Convergence.

[18][19][20] At the time, Marlinspike and Trevor Perrin started developing the Signal Protocol, an early version of which was first introduced in the TextSecure app in February 2014.

Notably, he published a 2002 paper on exploiting SSL/TLS implementations that did not correctly verify the X.509 v3 "BasicConstraints" extension in public key certificate chains.

[33][34] In 2011, Marlinspike presented a talk, "SSL And The Future Of Authenticity",[35] at the Black Hat security conference in Las Vegas.

[39] In 2012, Marlinspike and David Hulton presented research that makes it possible to reduce the security of MS-CHAPv2 handshakes to a single DES encryption.

[40] In 2013, Marlinspike published emails on his blog that he claimed were from Saudi Arabian telecom service Mobily soliciting his help in surveilling their customers, including intercepting communications running through various applications.

[41] Marlinspike says that when flying within the United States he is unable to print his own boarding pass, is required to have airline ticketing agents make a phone call in order to issue one, and is subjected to secondary screening at TSA security checkpoints.

Marlinspike refused to do this, and the devices were eventually returned, though he noted that he could no longer trust them, saying, "They could have modified the hardware or installed new keyboard firmware.

[4][48] In 2004, he bought a derelict sailboat and, with three friends, refurbished it and sailed around the Bahamas while making a "video zine" about their journey called Hold Fast.