Cryptography names: Alice, Bob, Eve


Since the late 1970s, cryptographers have been using personal names (instead of labels like “person A” and “person B”) to describe various communications scenarios. Many of these scenarios involve two communicating parties named Alice and Bob and an eavesdropper named Eve.

Extra parties are assigned names alphabetically (e.g., Carol, Dave) unless they play a specific role within the scenario. For instance, a password cracker is named Craig, a malicious attacker is named Mallory, an intruder is named Trudy, and a whistle-blower is named Wendy.

In zero-knowledge protocols, the “prover” and “verifier” of a message are typically named Peggy and Victor…but Pat and Vanna (after Wheel of Fortune presenters Pat Sajak and Vanna White) are sometimes used instead.

Here’s more about Alice and Bob from American cryptographer Bruce Schneier:

And you’d see paper after paper, and [in] the opening few paragraphs, the authors would explain what they’re doing in terms of Alice and Bob. So Alice and Bob have a storied history. They send each other secrets, they get locked in jail, they get married, they get divorced, they’re trying to date each other. Anything two people might want to do securely, Alice and Bob have done it somewhere in the cryptographic literature.

Question of the day: If you were tasked with updating the names of “person A” (female) and “person B” (male), what new names would you choose?


Image: Protocol by Randall Munroe under CC BY-NC 2.5.

4 thoughts on “Cryptography names: Alice, Bob, Eve

  1. Another pair of names you come across in game theory is Abelard and Eloise. Eloise has a winning strategy in a game if for All moves of Abelard there Exists a move of Eloise such that eventually Abelard has no legal moves left. Upside-down A and backwards-E are the formal symbols for the “all” and “exists” (or “there is”) quantifiers, and of course Abelard and Eloise are one of the most famous of medieval logicians and his wife, an ethicist.

  2. Thank you, Sara!

    I’m trying to read more about ∀ and Ǝ…I’ve never studied logic or game theory, though, so I’m finding it all pretty hard to interpret.

    Nonetheless I did learn that the names were chosen in the mid-1980s by British mathematician/logician Wilfred Hodges (who has an adorably old-school homepage). His words:

    “One can read ∀ as Abelard and Ǝ as Eloise — Peter Abelard was a twelfth-century Parisian logician who used to play games with Eloise, the niece of a canon of Notre Dame.”

    Source: Hodges, Wilfrid. Building Models by Games. Cambridge: Cambridge University Press, 1985.

  3. In another field of mathematics, game theory, the two player are names Belle Black (playing the “left” of “black” side of a game) and Wright White (playing the “right” or “white” side). The nice thing of having such a pair is that one can easily use the pronouns “she” and “he” to keep the language of explanations more flowing.

    A sample reference:

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