Quantum computing began in the early 1980s, when physicist Paul Benioff proposed a quantum mechanical model of the Turing machine.[3] Richard Feynman and Yuri Manin later suggested that a quantum computer could perform simulations that are out of reach for regular computers.[4][5] In 1994, Peter Shor developed a polynomial-time quantum algorithm for factoring integers.[6] This was a major breakthrough in the subject: an important method of asymmetric key exchange known as RSA is based on the belief that factoring integers is computationally difficult. The existence of a polynomial-time quantum algorithm proves that one of the most widely used cryptographic protocols is vulnerable to an adversary who possesses a quantum computer.