The names Alice and Bob are commonly used placeholder names for archetypal characters in fields such as cryptography and physics. The names are used for convenience, since explanations such as "Person A wants to send a message to person B" can be difficult to follow in complex systems involving many steps. Following the alphabet, the specific names have evolved into common parlance within these fields—helping technical topics to be explained in a more understandable fashion.

In cryptography and computer security, there are a number of widely used names for the participants in discussions and presentations about various protocols. The names are conventional, somewhat self-suggestive, sometimes humorous, and effectively act as metasyntactic variables.

In typical implementations of these protocols, it is understood that the actions attributed to characters such as Alice or Bob need not always be carried out by human parties directly, but also by a trusted automated agent (such as a computer program) on their behalf.

Alice and Bob. Generally, Alice wants to send a message to Bob. These names were used by Ron Rivest in the 1978 Communications of the ACM article presenting the RSA cryptosystem, and in A Method for Obtaining Digital Signatures and Public-Key Cryptosystems published April 4, 1977, revised September 1, 1977 as technical Memo LCS/TM82. Rivest denies that these names have any relation to the 1969 movie Bob & Carol & Ted & Alice as occasionally suggested by others.

This Video by Bruce Schneier about Alive and Bob :

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