Sarah Flannery (born 1982, County Cork, Ireland) was, at sixteen years old, the winner of the 1999 Esat Young Scientist Exhibition for development of the Cayley–Purser algorithm, based on work she had done with researchers at Baltimore Technologies during a brief internship there. The project, entitled "Cryptography – A new algorithm versus the RSA", also won her the EU Young Scientist of the Year Award for 1999. Her book In Code (2001), co-written with her father, mathematician David Flannery, retells the story of the making and breaking of the algorithm and of the enjoyment that she got, as a child and throughout her life, from solving mathematical puzzles.
Sarah Flannery is the daughter of David and Elaine Flannery. She has four younger brothers: Mick, Brian, David and Eamonn. Her oldest brother is the singer-songwriter Mick Flannery. Her education included a primary all-girls school and a secondary co-ed school.