Among computer scientists and programmers, there's the common habit of naming people in the context of security protocols e.g. Alice, Bob or Eve. Descriptions of more elaborate attack vector sometimes refer to Charlie (as does this XKCD strip), but is there a convention for additional participants?

  • 9
    Its all covered in Alice and Bob.
    – user40980
    Commented Jun 6, 2014 at 17:31
  • @MichaelT: Oops, how embarrassing. I thought of "security protocol names", "protocol participant", but not the most obvious... Thanks!
    – blubb
    Commented Jun 6, 2014 at 17:33

1 Answer 1


Alice and Bob were the first two described in Applied Cryptography. These are two people communicating and used a placeholder names. Keeping with a convention makes it easier for people to remember what role they play in communication.

Beyond Alice and Bob, the first letter of the name typically implies the role of the individual in the communication.

C is sometimes a third person, but other times C is a Cracker.

D is often a fourth person in communication.

E can either be a fifth person, but often E has Evil intent. Eve in particular is an Eavedropper.

F is a sixth person... and so on.

M becomes a Malicious attacker (as opposed to Eve, who just wants to eavesdrop).

O is an Opponent, similar to M, but not necessarily malicious.

P needs to have something Proven and V needs to have something Verified.

S is for Sybil which is a book about the treatment of a woman named Sybil Dorsett who had dissociative identity disorder. In the context of security names, Sybil is a particular type of attacker who uses many identities often in combination with a system that uses reputation.

T is Trusted.

W can either be a Warden who guards Alice and Bob or a Whistleblower with insider information.

Further reading:

  • Loved the placeholder page at wikipedia. Thanks for sharing.
    – DrBeco
    Commented Aug 22, 2015 at 21:04

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