Mihir Bellare
The cryptographer who made provable security something engineers could actually use – and a co-author of HMAC.
Mihir Bellare, a professor at UC San Diego, has spent his career on what he calls practice-oriented provable security: rather than proving asymptotic statements about idealised constructions, give concrete bounds on how much security a real scheme loses. With Phillip Rogaway he formalised the random oracle model in 1993 and designed OAEP the following year, which became the recommended padding for RSA encryption in PKCS #1 v2.
In 1996 he published HMAC with Ran Canetti and Hugo Krawczyk, and it went on to become standard in TLS, IPsec and almost every signed API request on the web. Few people have written so much cryptography that runs every second without anyone giving it a thought.