Alice and Bob

Alice and Bob are fictional characters commonly used in cryptology, as well as science and engineering literature. The Alice and Bob characters were invented by Ron Rivest, Adi Shamir, and Leonard Adleman in their 1978 paper "A method for obtaining digital signatures and public-key cryptosystems." Subsequently, they have become common archetypes in many scientific and engineering fields, such as quantum cryptography, game theory and physics. As the use of Alice and Bob became more popular, additional characters were added, each with a particular meaning.

Alice and Bob are the names of fictional characters used for convenience and to aid comprehension. For example, "How can Bob send a private message M to Alice in a public-key cryptosystem?" is believed to be easier to describe and understand than "How can B send a private message M to A in a public-key cryptosystem?"

In cryptography and computer security, Alice and Bob are used extensively as participants in discussions about cryptographic or systems. The names are conventional, and often use a rhyming mnemonic.

The first mention of Alice and Bob in the context of cryptography was in Rivest, Shamir, and Adleman's article, "A method for obtaining digital signatures and public-key cryptosystems." They wrote, "For our scenarios we suppose that A and B (also known as Alice and Bob) are two users of a public-key cryptosystem" (p. 121). Previous to this article, cryptographers typically referred to message senders and receivers as A and B, or other simple symbols. In fact, in the two previous articles by Rivest, Shamir, and Adleman, introducing the RSA cryptosystem, there is no mention of Alice and Bob.

Within a few years, however, reference 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, Tal Rabin begun 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."

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