Ron Rivest, Adi Shamir and Leonard Adleman

RSA cryptosystem

RSA is the first publicly described, usable public-key cryptosystem. It works by exploiting the asymmetry between modular exponentiation and root extraction modulo a composite number whose factorisation is secret. Its security depends on factoring difficulty—but that dependence is not proven equivalent. No published attack breaks it with large keys. It changed cryptography by enabling open protocols, trustless key exchange, and standardised role names like Alice and Bob.