Richard Kemmerer
The UCSB professor who gave the world a systematic way to hunt covert channels, rather than hoping someone stumbled on them.
A covert channel leaks information through something never meant for communication — a file that exists or doesn't, a CPU that is busy or idle. Kemmerer's Shared Resource Matrix of 1983 lists every shared resource and which operations can read or modify each of its attributes. Every cell where one party writes and another reads is a candidate. The method became standard practice in evaluations under the US Orange Book criteria.
He also worked on formal specification and verification of security kernels and cryptographic protocols, and on State Transition Analysis for intrusion detection. At UC Santa Barbara he and Giovanni Vigna built one of academia's most prolific security groups.