Mathy Vanhoef researches on stream-ciphers, discovered a new attack on RC4 that made it possible to exploit RC4 as used in TLS in practice (the RC4 NOMORE attack), and found the HEIST attack against TLS. He also focuses on wireless security, where he turns commodity wifi cards into state-of-the-art jammers, defeats MAC address randomization, and breaks protocols like WPA-TKIP.