Bennett, 82, is a fellow at technology company IBM in New York, while Brassard, 70, is a professor at the University of Montreal. The pair met by chance whilst attending an academic conference in Puerto Rico in 1979.
Bennett is reported to have approached the computer scientist as they were swimming during a break to suggest the idea of developing a banknote that could never be forged.
It heralded decades of co-operation, during which the two men developed a technique based on quantum physics – the behaviour of particles of matter, including electrons and photons.
Current encryption technology relies on complex mathematical combinations, but many scientists believe that the arrival of quantum computers will make this insecure.
By contrast, Bennett and Brassard’s theory – known as BB84 – shows that any attempt to hack or copy their quantum encryption key changes the very behaviour of its elements, making replication impossible.
In the announcement on Wednesday, the Association of Computer Machinery – the body that awards the Turing Award, praised their work as a “pathway toward securing digital communications in the decades ahead”.