Within a few years, however, references to Alice and Bob in cryptological literature became a common trope. Cryptographers would often begin their academic papers with reference to Alice and Bob. For instance, Michael Rabin began his 1981 paper, "Bob and Alice each have a secret, SB and SA, respectively, which they want to exchange." Early on, Alice and Bob were starting to appear in other domains, such as in Manuel Blum's 1981 article, "Coin Flipping by Telephone: A Protocol for Solving Impossible Problems," which begins, "Alice and Bob want to flip a coin by telephone."