Alice and Bob

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Alice and Bob.

When the interaction between two hypothetical characters is needed to explain or describe some system, they are nearly always called Alice and Bob. Alice and Bob - A and B. This duo originally started out in 1978 as a standardized way to explain cryptography. Over time, this Metasyntactic Variable duo has been adopted in explanations of mathematics, physics, quantum effects, and other arcane places, but have also been seen in fiction. They are also found in a surprising number of trope definitions.

Where more than two characters are needed, other names are used, such as Carol and Charlie. Some names have acquired standard meanings, such as Eve the Eavesdropper. Lists of these can be found in Bruce Schneier's book Applied Cryptography, and at that other wiki.

Note that the most common names are "Alice", "Bob" and "Charlie/Charley". This works for most situations.

The use of Alice and Bob is suggested in General Suggestions, but some of us (notably those who really are called Alice and/or Bob) sometimes wish a little imagination could be applied. That's where Aerith and Bob come in. Or Jim and Mary. Or Dick and Jane.

See also Girl A, Those Two Guys, Greek Chorus.

Not to be confused with Alice and Kev.

Examples of Alice and Bob include:

Film

• Movie and TV example: Bob & Carol & Ted & Alice.
• The main characters of the 2003 film Xtracurricular are Ally Koch, Brittney Kornblum and Chris Koenig. (Then again, the film was inspired by the anime Project A-ko, which approaches this trope through the related trope Girl A.)

Literature

• In most cryptography textbooks, communications are presented as being between Alice and Bob, and must be secured from a third-party interloper named Eve (for Eavesdropper, of course!). If the problem requires the involvement of more than two parties, then Charlie and Donna may be introduced. (This is the basis for the xkcd reference listed below.) Other character names sometimes used for special purposes include Mallory (a malicious active adversary, capable of changing the messages sent between Alice and Bob, whereas Eve merely listens), Trent (a mutually trusted third party, whom Alice and Bob might prevail upon to execute protocols in which they don't trust each other), and Peggy and Victor (the prover and verifier, respectively, in zero-knowledge proofs).
  • Game Theory books often use an adaptation of Alice and Bob in "Rose and Colin" (rows and columns on game theory charts), with "Larry", or "layer" thrown in for three person games.
    • Game Semantics books tend to use Abelard and Eloise (for resemblance to the universal and existental quantifier symbols, which are an inverted A and a backwards E). They are also the names of a medieval logician and his lover.
• Alice and Bob are the names of the parents in Vernor Vinge's Rainbows End, and a government official is named Eve Mallory.
• E. R. Emmet's "Our Factory" puzzles feature "Alf", "Bert", "Charlie", and so on.

Live-Action TV

• TV and Movie example: Bob & Carol & Ted & Alice.
• One of the logos at the end of The Bonnie Hunt Show (2008-2010) is for "Bob & Alice Productions".
  • Bonnie's Hunt's parents are named Bob and Alice so it is either just a reference to her parents or both.

Music

• Nerdcore Rap artist MC Plus+ has a song about cryptography named "Alice and Bob".

Newspaper Comics

• Dilbert does this in a one-way fashion with "Ted the Generic Guy", who has no consistent personality and shows up whenever a generic extra is needed. Bad things tend to happen to him.

Oral Tradition

• The Story of Alice and Bob is a humorous after-dinner speech recounting their mythology.
• A collection of quantum-computing Alice and Bob jokes.

Video Games

• Used in a very surreal Cyberspace level in World of Goo called "Alice and Bob and the Third Party," where you intercept information-goo transmitted from cosmicGrrrl! to LaconicCrusadr13.
• Used as examples for an explanation of quantum teleportation in Remember 11.

Web Comics

• xkcd:
  • Eve gets her say in "Alice and Bob".
  • Taken literally in "Encryption".
• Alice is introduced in the opening chapter of Freak Angels. In the epilogue, she's explaining the story to a military officer named Bob.

Web Original

• Catalog Living has the imaginary Elaine and Gary.

Real Life

• Alice and Bob really are quantum -- a professor at the University of Washington has used two separate remote cameras, named Alice and Bob, to test the theory of non-locality and its potential for time travel, by attempting to receive a message before it's sent. The experiment hasn't yielded results so far^[when?], but it's telling.
• In Linguistics, it's more often John and Mary.
• Named tropical storms (typhoons, hurricanes, cyclones) are based on a sequential list of given names, replaced every year, with a different list for each region. The lists will be re-used at half-dozen year intervals, but with the names of historic "worst" storms periodically retired. That'd make Hurricane Andrew the first (A) tropical storm of the North Atlantic hurricane season in his respective year. Q, U, Z are not used; a particularly bad season (such as 2005 with Dennis, Katrina, Wilma) can exhaust the entire 23-name alphabetical list, after which the Greek alphabet (Hurricane Beta...) is pressed into service. The original lists used female names as meteorologists proposed the names of their sweethearts; more recent practice has alternated gender on each successive storm (so Alex, Brenda, Charles, Diana, Elmer, Francesca... or a similar pattern).
  • A similar alphabetically-sequential naming series was used circa-1883 for a string of Atlantic and Pacific Railroad stops where steam trains took on water across the Mojave Desert. The first was "Amboy", now a ghost town on the former US Route 66. followed (from west to east) with Bristol, Cadiz, Danby, Essex, Fenner, Goffs, Home, Ibis, Java, and Klinefelter. Most of these points are now abandoned.
  • Similar alphabetically-sequential naming patterns have been used for versions of software; Ubuntu uses names of animals this way, while the Android OS used to use names of foodstuffs (beginning after 'B' as the base, "Cupcake", "Donut", Éclair", "Froyo", "Gingerbread", "Honeycomb", "Ice Cream Sandwich", "Jelly Bean", "KitKat", "Lollipop", "Marshmallow", "Nougat", "Oreo", "Pie", ending just before this reached 'Q').
  • In 2012, The Weather Channel began naming winter storms starting with "Winter Storm Athena", a nor'easter that hit the Eastern United States and Canada in early November of that year. As of this writing (Fall 2021), this remains a practice exclusive to The Weather Channel, with both the US National Weather Service and competing weather forecasters like AccuWeather rejecting outright the use of names for winter storms.

All The Tropes

Alice and Bob appear on

• all of these pages.
• Numerous Playing With pages.
• ? and more.