Sarah Flannery

The Cayley–Purser algorithm replaced modular exponentiation with multiplication of 2×2 matrices and ran considerably faster than RSA. It won her both the Irish and the European Young Scientist competitions in 1999, along with a press frenzy that cast a sixteen-year-old as the end of the crypto industry.

The impressive part came later: an attack on the scheme was found, and she laid it out openly in her book In Code (2000), written with her father David. That is a better lesson in how cryptography is supposed to work than most algorithms that survived – nothing is secure until other people have tried hard to break it.