RSA

RSA is a public-key cryptosystem named after its inventors Ron Rivest, Adi Shamir, and Leonard Adleman, who published it in 1977. It is one of the first practical public-key encryption systems and remains widely used for secure data transmission.

The security of RSA rests on the practical difficulty of factoring the product of two large prime numbers. This is a mathematical problem that is believed to be computationally intractable for sufficiently large keys, though no proof of this intractability exists. The advent of quantum computing threatens RSA's security foundation, as Shor's algorithm can factor integers in polynomial time on a quantum computer.

RSA is a foundational example in coding theory and information theory: it demonstrates that computational hardness assumptions can be used to construct practical security guarantees, bridging the gap between mathematical theory and engineering implementation.