Placeholder Names In Cryptography
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Alice and Bob are fictional characters commonly used as placeholders in discussions about
cryptographic Cryptography, or cryptology (from "hidden, secret"; and ''graphein'', "to write", or '' -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adversarial behavior. More gen ...
systems and
protocols Protocol may refer to: Sociology and politics * Protocol (politics), a formal agreement between nation states * Protocol (diplomacy), the etiquette of diplomacy and affairs of state * Etiquette, a code of personal behavior Science and technology ...
, and in other science and engineering literature where there are several participants in a
thought experiment A thought experiment is an imaginary scenario that is meant to elucidate or test an argument or theory. It is often an experiment that would be hard, impossible, or unethical to actually perform. It can also be an abstract hypothetical that is ...
. The Alice and Bob characters were created by
Ron Rivest Ronald Linn Rivest (; born May 6, 1947) is an American cryptographer and computer scientist whose work has spanned the fields of algorithms and combinatorics, cryptography, machine learning, and election integrity. He is an Institute Profess ...
,
Adi Shamir Adi Shamir (; born July 6, 1952) is an Israeli cryptographer and inventor. He is a co-inventor of the Rivest–Shamir–Adleman (RSA) algorithm (along with Ron Rivest and Len Adleman), a co-inventor of the Feige–Fiat–Shamir identification sc ...
, and
Leonard Adleman Leonard Adleman (born December 31, 1945) is an American computer scientist. He is one of the creators of the RSA encryption algorithm, for which he received the 2002 Turing Award. He is also known for the creation of the field of DNA computin ...
in their 1978 paper "A Method for Obtaining Digital Signatures and Public-key Cryptosystems". Subsequently, they have become common
archetype The concept of an archetype ( ) appears in areas relating to behavior, historical psychology, philosophy and literary analysis. An archetype can be any of the following: # a statement, pattern of behavior, prototype, "first" form, or a main mo ...
s in many scientific and engineering fields, such as
quantum cryptography Quantum cryptography is the science of exploiting quantum mechanical properties to perform cryptographic tasks. The best known example of quantum cryptography is quantum key distribution, which offers an information-theoretically secure soluti ...
,
game theory Game theory is the study of mathematical models of strategic interactions. It has applications in many fields of social science, and is used extensively in economics, logic, systems science and computer science. Initially, game theory addressed ...
and
physics Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...
. As the use of Alice and Bob became more widespread, additional characters were added, sometimes each with a particular meaning. These characters do not have to refer to people; they refer to generic agents which might be different computers or even different programs running on a single computer.


Overview

Alice and Bob are the names of fictional characters used for convenience and to aid comprehension. For example, "How can Bob send a private message M to Alice in a public-key cryptosystem?" is believed to be easier to describe and understand than if the hypothetical people were simply named ''A'' and ''B'' as in "How can B send a private message M to A in a
public-key cryptosystem Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic a ...
?" The names are conventional, and where relevant may use an
alliterative Alliteration is the repetition of syllable-initial consonant sounds between nearby words, or of syllable-initial vowels if the syllables in question do not start with a consonant. It is often used as a List of narrative techniques#Style, litera ...
mnemonic A mnemonic device ( ), memory trick or memory device is any learning technique that aids information retention or retrieval in the human memory, often by associating the information with something that is easier to remember. It makes use of e ...
such as "Mallory" for "malicious" to associate the name with the typical role of that person.


History

Scientific papers about thought experiments with several participants often used letters to identify them: ''A'', ''B'', ''C'', etc. The first mention of Alice and Bob in the context of cryptography was in Rivest, Shamir, and Adleman's 1978 article "A method for obtaining digital signatures and public-key cryptosystems." They wrote, "For our scenarios we suppose that A and B (also known as Alice and Bob) are two users of a public-key cryptosystem". Previous to this article, cryptographers typically referred to message senders and receivers as A and B, or other simple symbols. In fact, in the two previous articles by Rivest, Shamir, and Adleman, introducing the
RSA cryptosystem The RSA (Rivest–Shamir–Adleman) cryptosystem is a public-key cryptosystem, one of the oldest widely used for secure data transmission. The initialism "RSA" comes from the surnames of Ron Rivest, Adi Shamir and Leonard Adleman, who publicly ...
, there is no mention of Alice and Bob. The choice of the first three names may have come from the film ''
Bob & Carol & Ted & Alice ''Bob & Carol & Ted & Alice'' is a 1969 American comedy-drama film directed by Paul Mazursky, written by Mazursky and Larry Tucker (screenwriter), Larry Tucker, who also produced the film, and starring Natalie Wood, Robert Culp, Elliott Gould, ...
''. Within a few years, however, references to Alice and Bob in cryptological literature became a common trope. Cryptographers would often begin their academic papers with reference to Alice and Bob. For instance, Michael Rabin began his 1981 paper, "Bob and Alice each have a secret, SB and SA, respectively, which they want to exchange." Early on, Alice and Bob were starting to appear in other domains, such as in
Manuel Blum Manuel Blum (born 26 April 1938) is a Venezuelan-born American computer scientist who received the Turing Award in 1995 "In recognition of his contributions to the foundations of computational complexity theory and its application to cryptography ...
's 1981 article, "Coin Flipping by Telephone: A Protocol for Solving Impossible Problems," which begins, "Alice and Bob want to flip a coin by telephone." Although Alice and Bob were invented with no reference to their personality, authors soon began adding colorful descriptions. In 1983, Blum invented a backstory about a troubled relationship between Alice and Bob, writing, "Alice and Bob, recently divorced, mutually distrustful, still do business together. They live on opposite coasts, communicate mainly by telephone, and use their computers to transact business over the telephone." In 1984, John Gordon delivered his famous "After Dinner Speech" about Alice and Bob, which he imagines to be the first "definitive biography of Alice and Bob." In addition to adding backstories and personalities to Alice and Bob, authors soon added other characters, with their own personalities. The first to be added was Eve, the "eavesdropper." Eve was invented in 1988 by Charles Bennet, Gilles Brassard, and Jean-Marc Robert, in their paper, "Privacy Amplification by Public Discussion." In
Bruce Schneier Bruce Schneier (; born January 15, 1963) is an American cryptographer, computer security professional, privacy specialist, and writer. Schneier is an Adjunct Lecturer in Public Policy at the Harvard Kennedy School and a Fellow at the Berkman ...
's book ''Applied Cryptography'', other characters are listed.


Cast of characters


Cryptographic systems

The most common characters are Alice and Bob. Eve, Mallory, and Trent are also common names, and have fairly well-established "personalities" (or functions). The names often use alliterative mnemonics (for example, Eve, "eavesdropper"; Mallory, "malicious") where different players have different motives. Other names are much less common and more flexible in use. Sometimes the genders are alternated: Alice, Bob, Carol, Dave, Eve, etc.


Interactive proof systems

For interactive proof systems there are other characters:


Physics

The names Alice and Bob are often used to name the participants in thought experiments in physics. More alphabetical names, usually of alternating gender, are used as required, e.g. "Alice and Bob (and Carol and Dick and Eve)". In experiments involving robotic systems, the terms "Alice Robot" and "Bob Robot" refer to mobile platforms responsible for transmitting quantum information and receiving it with quantum detectors, respectively, within the context of the field of quantum robotics.Farbod Khoshnoud, Marco B. Quadrelli, Enrique Galvez, Clarence W. de Silva, Shayan Javaherian, B. Bahr, M. Ghazinejad, A. S. Eddin, M. El-Hadedy, Quantum Brain-Computer Interface, ASEE PSW, 2023, in press.


See also

*
Diffie–Hellman key exchange Diffie–Hellman (DH) key exchangeSynonyms of Diffie–Hellman key exchange include: * Diffie–Hellman–Merkle key exchange * Diffie–Hellman key agreement * Diffie–Hellman key establishment * Diffie–Hellman key negotiation * Exponential ke ...
*
Martin Gardner Martin Gardner (October 21, 1914May 22, 2010) was an American popular mathematics and popular science writer with interests also encompassing magic, scientific skepticism, micromagic, philosophy, religion, and literatureespecially the writin ...
*
Public-key cryptography Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic alg ...
* Security protocol notation


References


External links


History of Alice and Bob

A Method for Obtaining Digital Signatures and Public-Key Cryptosystems


given at the Zurich Seminar, April 1984, by John Gordon
Geek Song: "Alice and Bob"


(mainly
Quantum Computing A quantum computer is a computer that exploits quantum mechanical phenomena. On small scales, physical matter exhibits properties of wave-particle duality, both particles and waves, and quantum computing takes advantage of this behavior using s ...
-related)
A short history of Bobs (story and slideshow) in the computing industry, from Alice & Bob to Microsoft Bob and Father of Ethernet Bob Metcalfe

XKCD #177: Alice and Bob
{{DEFAULTSORT:Alice And Bob Cryptographic protocols Placeholder names Thought experiments in physics Fictional duos History of computing