Loren Kohnfelder invented what is today called public key infrastructure (PKI) in his May 1978 MIT S.B. (BSCSE) thesis, which described a practical means of using public key cryptography to secure network communications.
The Kohnfelder thesis introduced[1] the terms "certificate" and "certificate revocation list" as well as numerous other concepts now established as important parts of PKI. The X.509 certificate specification that provides the basis for SSL, S/MIME and most modern PKI implementations are based Kohnfelder's thesis.[2]
He was also the co-creator, with Praerit Garg, of the STRIDE model of security threats, widely used in threat modeling.
In 2021 he published the book Designing Secure Software with No Starch Press.[3]