Algorhythms: Alice and Bob

Algorhythms: Alice and Bob Alice and Bob from the album Algorhythms by MC Plus+ (via Reddit).

If you’re not familiar, Alice, Bob and Eve are example characters used to illustrate encryption scenarios in Bruce Schneier’s Applied Cryptography.

There are a whole host of characters. This would make a pretty good dramatis personae for a screenplay…

This list is drawn mostly from the book Applied Cryptography by Bruce Schneier. Alice and Bob are archetypes in cryptography; Eve is also common. Names further down the alphabet are less common.

  • 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.[citation needed]
  • Carol, Carlos or Charlie, as a third participant in communications.
  • Chuck, as a third participant usually of malicious intent.[1]
  • Dave, a fourth participant, and so on alphabetically.
  •  Eve, an eavesdropper, is usually a passive attacker. While she can listen in on messages between Alice and Bob, she cannot modify them. In quantum cryptography, Eve may also represent the environment.
  • Fran, for Fran Allen, Turing award winner
  • Gordon, a government agent.
  • Isaac, an Internet Service Provider (ISP).
  • Ivan, an issuer (as in financial cryptography).
  • Justin, or Julian from the justice system.
  •  Mallory, a malicious attacker; unlike Eve, Mallory can modify messages, substitute her own messages, replay old messages, and so on. The problem of securing a system against Mallory is much greater than against Eve. The names Marvin, Mallet, and Moriarty can also be used for this role.
  • Matilda, a merchant (as in e-commerce or financial cryptography).
  • Oscar, an opponent, is usually taken as equivalent to Mallory.
  • Pat or Peggy, a prover, and Victor, a verifier, often must interact in some way to show that the intended transaction has actually taken place. They are often found in zero-knowledge proofs. Another name pair sometimes used is Pat and Vanna (after the host and hostess on the Wheel of Fortune television show).
  • Plod, a law enforcement officer from the children’s fictional character Mr. Plod, in the Noddy books by Enid Blyton.
  • Steve, sometimes used in reference to Steganography.
  • Trent, a trusted arbitrator, is some kind of neutral third party, whose exact role varies with the protocol under discussion.
  • Trudy, an intruder: another alternative to Mallory.
  • Vanna or Victor: see Pat or Peggy above
  • Walter, a warden, may be needed to guard Alice and Bob in some respect, depending on the protocol being discussed.
  • Zoe, often the last party to be involved in a cryptographic protocol.

Although an interactive proof system is not quite a cryptographic protocol, it is sufficiently related to mention the cast of characters its literature features:

  • Arthur and Merlin: In interactive proof systems, the prover has unbounded computational ability and is hence associated with Merlin, the powerful wizard. He claims the truth of a statement, and Arthur, the wise king, questions him to verify the claim. These two characters also give the name for two complexity classes, namely MA and AM.

A similar pair of characters is Paul and Carole. The characters were introduced in the solution of the Twenty Questions problem,[2] where “Paul”, who asked questions, stood for Paul Erdős and “Carole”, who answered them, was an anagram of “oracle”. They were further used in certain combinatorial games in the roles of Pusher and Chooser respectively, and have since been used in various roles.[3]

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