 The algorithms just described, although demonstrating the potential superiority of quantum computers over their classical counterparts, nevertheless deal with apparently unimportant computational problems. Moreover the speed-ups in each of them are only relative to their respective oracles. It is doubtful whether research into quantum computing would have attracted so much attention and evolved to its current status if its merit could be demonstrated only with these problems. But in 1994, Peter Shor realised that Simon’s algorithm could be harnessed to solve a much more interesting and crucial problem, namely factoring, which lies at the heart of current cryptographic protocols such as RSA (Rivest, Shamir, and Adleman 1978). Shor’s algorithm has turned quantum computing into one of the most exciting research domains in quantum mechanics.