In the 1980s, Charles Bennett and Gilles Brassard created a new kind of encryption that would be impregnable. For their pivotal discovery, Bennett and Brassard has just been awarded this year’s Turing Award, widely regarded as the Nobel Prize for computing.  This is their story.

Charles Henry Bennett (born 1943) is an American physicist, information theorist and IBM Fellow at IBM Research. Gilles Brassard (b. 1955) a Canadian computer scientist and faculty member at the University of Montreal. The two met in 1979 at an academic conference where Dr Brassard was presenting his graduate work on the mathematical foundations of cryptography. While swimming off the coast of Puerto Rico to take a break from the conference, Bennett swam up to Brassard, then only 24, suggesting they use quantum mechanics to create a bank note that could never be forged. Their collaboration led to the development of quantum cryptography to encrypt, transmit and decode information securely.

Called BB84, their system used photons (particles of light) as the key to lock and unlock digital data. Thanks to the laws of quantum mechanics, the behavior of a photon changes if someone looks at it, which means that if anyone tries to steal the keys, he or she will leave telltale evidence of the attempted theft, a bit like breaking the seal of an aspirin bottle.

The importance of their work became apparent ten years later, when mathematician Peter Shor discovered that a hypothetical quantum computer cannot guarantee the privacy and security of data transmitted across networks unless it is protected by quantum cryptography. Today, quantum cryptography has emerged as an important method for ensuring the security of digital communication in diverse fields such as satellite communications, military intelligence, banking and finance.

In later work, Brassard and Bennett demonstrated the practical usefulness of quantum teleportation, the idea that quantum information could be transmitted between distant locations using quantum entanglement (a strange phenomenon where the quantum state of two particles remains connected, even when they are too far apart to influence each other). Their work laid the foundation for ensuring security in data transmitted across quantum computers no matter where there are located, a matter of paramount importance as the world strives toward the age of quantum networks and quantum internet

“Bennett and Brassard fundamentally changed our understanding of information itself,” Yannis Ioannidis, president of the ACM, said in a statement. “Their insights expanded the boundaries of computing and set in motion decades of discovery across disciplines. The global momentum behind quantum technologies today underscores the enduring importance of their contributions.”