Alice and Bob#Cast of characters

{{Short description|Characters used in cryptography and science literature}}

Alice and Bob are fictional characters commonly used as placeholders in discussions about cryptographic systems and protocols,{{Ref RFC|4949|notes=no}} and in other science and engineering literature where there are several participants in a thought experiment. The Alice and Bob characters were created by Ron Rivest, Adi Shamir, and Leonard Adleman in their 1978 paper "A Method for Obtaining Digital Signatures and Public-key Cryptosystems".{{Cite journal |last1=Rivest |first1=Ron L. |author-link1=Ron Rivest |first2=Adi |last2=Shamir |author-link2=Adi Shamir |first3=Len |last3=Adleman |author-link3=Leonard Adleman |date=1978-02-01 |title=A Method for Obtaining Digital Signatures and Public-key Cryptosystems |journal=Communications of the ACM |volume=21 |issue=2 |pages=120–126 |doi=10.1145/359340.359342 |issn=0001-0782 |citeseerx=10.1.1.607.2677|s2cid=2873616 }} Subsequently, they have become common archetypes in many scientific and engineering fields, such as quantum cryptography, game theory and physics.{{cite book|last=Newton|first=David E.|title=Encyclopedia of Cryptography|year=1997|publisher=Instructional Horizons, Inc|location=Santa Barbara California|pages=10}} 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

File:Public key shared secret.svg

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?"

The names are conventional, and where relevant may use an alliterative mnemonic 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".{{rp|121}} 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, there is no mention of Alice and Bob.{{cite book |last1=Rivest |first1=Ron L. |author-link1=Ron Rivest |first2=Adi |last2=Shamir |author-link2=Adi Shamir |first3=Len |last3=Adleman |author-link3=Leonard Adleman |title=On Digital Signatures and Public-Key Cryptosystems |location=Cambridge MA |publisher=Massachusetts Institute of Technology |date=April 1977}}{{cite book |last1=Rivest |first1=Ron L. |author-link1=Ron Rivest |first2=Adi |last2=Shamir |author-link2=Adi Shamir |first3=Len |last3=Adleman |author-link3=Leonard Adleman |title=Cryptographic Communications System and Method |id=4405829 |location=Cambridge MA |orig-year=1977 |date=September 20, 1983}} The choice of the first three names may have come from the film Bob & Carol & Ted & Alice.{{cite web |url=https://www.networkworld.com/article/2318241/lan-wan-security-s-inseparable-couple.html |title=Security's inseparable couple: Alice & Bob |website=NetworkWorld |date=7 February 2005 |first=Bob |last=Brown}}

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."{{cite book |last=Rabin |first=Michael O. |author-link=Michael O. Rabin |title=How to exchange secrets with oblivious transfer |id=Technical Report TR-81 |publisher=Aiken Computation Lab, Harvard University |date=1981}} Early on, Alice and Bob were starting to appear in other domains, such as in Manuel Blum'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."{{cite journal |last=Blum |first=Manuel |author-link=Manuel Blum |title=Coin Flipping by Telephone a Protocol for Solving Impossible Problems |journal=ACM SIGACT News |volume=15 |issue=1 |date=November 10, 1981 |pages=23–27|doi=10.1145/1008908.1008911 |s2cid=19928725 |doi-access=free }}

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."{{Cite journal |doi=10.1145/357360.357368 |title=How to exchange (Secret) keys |year=1983 |last1=Blum |first1=Manuel |author-link=Manuel Blum |journal=ACM Transactions on Computer Systems |volume=1 |issue=2 |pages=175–193|s2cid=16304470 |doi-access=free }} In 1984, John Gordon delivered his famous{{cite journal |title=Visualization of cryptographic protocols with GRACE |doi=10.1016/j.jvlc.2007.05.001 |journal=Journal of Visual Languages & Computing |volume=19 |issue=2 |date=April 2008 |pages=258–290 |first1=Giuseppe |last1=Cattaneoa |first2=Alfredo |last2=De Santisa |first3=Umberto |last3=Ferraro Petrillo}} "After Dinner Speech" about Alice and Bob, which he imagines to be the first "definitive biography of Alice and Bob."{{cite web |last=Gordon |first=John |title=The Alice and Bob After Dinner Speech |location=Zurich |date=April 1984 |url=http://downlode.org/Etext/alicebob.html}}

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."{{cite journal |doi=10.1137/0217014 |title=Privacy Amplification by Public Discussion |year=1988 |last1=Bennett |first1=Charles H. |last2=Brassard |first2=Gilles |last3=Robert |first3=Jean-Marc |journal=SIAM Journal on Computing |volume=17 |issue=2 |pages=210–229|s2cid=5956782 }} In Bruce Schneier's book Applied Cryptography, other characters are listed.{{cite book |last=Schneier |first=Bruce |author-link=Bruce Schneier |title=Applied Cryptography: Protocols, Algorithms and Source Code in C |location=Hoboken, NJ |publisher=John Wiley & Sons |date=2015 |isbn=978-0-471-59756-8}}

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.{{cite journal|last1=Xue|first1=Peng|last2=Wang|first2=Kunkun|last3=Wang|first3=Xiaoping|title=Efficient multiuser quantum cryptography network based on entanglement|journal=Scientific Reports|volume=7|issue=1|year=2017|page=45928|issn=2045-2322|doi=10.1038/srep45928|pmid=28374854|pmc=5379677|bibcode=2017NatSR...745928X|doi-access=free}} An example from quantum cryptography with Alice, Bob, Carol, and David.

class="wikitable"

Alice and Bob

| The original, generic characters. Generally, Alice and Bob want to exchange a message or cryptographic key.

Carol, Carlos or Charlie

| A generic third participant.

Chuck or Chad

| A third participant, usually of malicious intent.{{cite book |last=Tanenbaum |first=Andrew S. |title=Distributed Systems: Principles and Paradigms |isbn=978-0-13-239227-3 | publisher=Pearson Prentice Hall |year=2007 |url=https://books.google.com/books?id=DL8ZAQAAIAAJ |page=171;399–402 }}

Craig

| A password cracker, often encountered in situations with stored passwords.

Dan, Dave or David

A generic fourth participant.

Erin

| A generic fifth participant, but rarely used, as "E" is usually reserved for Eve.

{{Anchor|Eve}}Eve or Yves

| An eavesdropper, who is usually a passive attacker. While they can listen in on messages between Alice and Bob, they cannot modify them. In quantum cryptography, Eve may also represent the environment.{{clarify|date=November 2018}}

Faythe

| A trusted advisor, courier or intermediary. Faythe is used infrequently, and is associated with faith and faithfulness. Faythe may be a repository of key service or courier of shared secrets.{{citation needed|date=March 2016}}

Frank

| A generic sixth participant.

Grace

| A government representative. For example, Grace may try to force Alice or Bob to implement backdoors in their protocols. Grace may also deliberately weaken standards.{{cite arXiv |eprint=2003.11511 |last1=Cho |first1=Hyunghoon |last2=Ippolito |first2=Daphne |author3=Yun William Yu |title=Contact Tracing Mobile Apps for COVID-19: Privacy Considerations and Related Trade-offs |year=2020 |class=cs.CR }}

Heidi

| A mischievous designer for cryptographic standards, but rarely used.{{Cite book |last1=Fried |first1=Joshua |last2=Gaudry |first2=Pierrick |last3=Heninger |first3=Nadia |author3-link=Nadia Heninger |last4=Thomé |first4=Emmanuel |title=Advances in Cryptology – EUROCRYPT 2017 |chapter=A Kilobit Hidden SNFS Discrete Logarithm Computation |url=https://eprint.iacr.org/2016/961.pdf |publisher=University of Pennsylvania and INRIA, CNRS, University of Lorraine |series=Lecture Notes in Computer Science |date=2017 |volume=10,210 |pages=202–231 |doi=10.1007/978-3-319-56620-7_8 |arxiv=1610.02874 |isbn=978-3-319-56619-1 |s2cid=12341745 |access-date=2016-10-12}}

Ivan

| An issuer, mentioned first by Ian Grigg in the context of Ricardian contracts.{{Cite web|last=Grigg|first=Ian|title=Ivan The Honourable|url=http://iang.org/rants/ivan_the_honourable.html| website=iang.org | date=2002-11-24}}

Judy

| A judge who may be called upon to resolve a potential dispute between participants. See Judge Judy.

{{Anchor|Mallory}}{{Anchor|Mallet}}{{Anchor|Trudy}}Mallory{{cite journal |last=Szabo |first=Nick |author-link=Nick Szabo |date=September 1997 |title=Formalizing and Securing Relationships on Public Networks |url=http://firstmonday.org/ojs/index.php/fm/article/view/548/469 |journal=First Monday|volume=2 |issue=9 |doi=10.5210/fm.v2i9.548|s2cid=33773111 |doi-access=free }}{{citation |last=Schneier|first=Bruce |author-link=Bruce Schneier |title=Who are Alice & Bob? |date=2010-09-23 |url=https://www.youtube.com/watch?v=BuUSi_QvFLY |archive-url=https://ghostarchive.org/varchive/youtube/20211222/BuUSi_QvFLY |archive-date=2021-12-22 |url-status=live|access-date=2017-05-02 |website=YouTube}}{{cbignore}} or (less commonly) Mallet or Darth

| A malicious attacker. Associated with Trudy, an intruder. Unlike the passive Eve, Mallory is an active attacker (often used in man-in-the-middle attacks), who can modify messages, substitute messages, or replay old messages. The difficulty of securing a system against a Mallory is much greater than against an Eve.

Michael or Mike

| Used as an alternative to the eavesdropper Eve, from microphone.

Niaj

| Used as an alternative to the eavesdropper Eve in several South Asian nations.{{Cite web|title=A Collaborative Access Control Framework for Online Social Networks|url=http://raulpardo.net/papers/JLAMP2020.pdf}}

Olivia

| An oracle, who responds to queries from other participants. Olivia often acts as a "black box" with some concealed state or information, or as a random oracle.

Oscar

| An opponent, similar to Mallory, but not necessarily malicious.

Peggy or Pat

| A prover, who interacts with the verifier to show that the intended transaction has actually taken place. Peggy is often found in zero-knowledge proofs.

Rupert

| A repudiator who appears for interactions that desire non-repudiation.

Sybil

| A pseudonymous attacker, who usually uses a large number of identities. For example, Sybil may attempt to subvert a reputation system. See Sybil attack.

Trent or Ted

| A trusted arbitrator, who acts as a neutral third party.

Trudy

| An intruder.

Victor or Vanna{{cite journal |year=1992 |title=Algebraic Methods for Interactive Proof Systems |journal=Journal of the ACM |volume=39 |issue=4 |pages=859–868 |doi=10.1145/146585.146605 |author-link=Carsten Lund |first=Carsten |last=Lund |display-authors=etal |citeseerx=10.1.1.41.9477|s2cid=207170996 }}

| A verifier, who requires proof from the prover.

Walter

| A warden, who may guard Alice and Bob.

Wendy

| A whistleblower, who is an insider with privileged access capable of divulging information.

=Interactive proof systems=

For interactive proof systems there are other characters:

class="wikitable"

Arthur and Merlin

| Merlin provides answers, and Arthur asks questions.{{cite journal |last1=Babai |first1=László |last2=Moran |first2=Shlomo |title=Arthur-Merlin games: A randomized proof system, and a hierarchy of complexity classes |journal=Journal of Computer and System Sciences |date=April 1988 |volume=36 |issue=2 |pages=254–276 |doi=10.1016/0022-0000(88)90028-1 |doi-access=free }} Merlin has unbounded computational ability (like the wizard Merlin). In interactive proof systems, Merlin claims the truth of a statement, and Arthur (like King Arthur), questions him to verify the claim.

Paul and Carole

| Paul asks questions, and Carole provides answers. In the solution of the Twenty Questions problem,{{citation |doi=10.1017/S0963548300000080 |last1=Spencer |first1=Joel |author1-link=Joel Spencer |last2=Winkler |first2=Peter |author2-link=Peter Winkler |title=Three Thresholds for a Liar |url=http://math.dartmouth.edu/~pw/papers/3thresh.ps |journal=Combinatorics, Probability and Computing |year=1992 |volume=1 |issue=1 |pages=81–93|s2cid=45707043 }} Paul (standing in for Paul Erdős) asked questions and Carole (an anagram of "oracle") answered them. Paul and Carole were also used in combinatorial games, in the roles of pusher and chooser.{{cite book |last=Muthukrishnan |first=S. |author-link=S. Muthukrishnan (computer scientist) |title=Data Streams: Algorithms and Applications |isbn=978-1-933019-14-7 |publisher=Now Publishers |year=2005 |url=http://algo.research.googlepages.com/eight.ps |page=3 }}{{Dead link|date=August 2023 |bot=InternetArchiveBot |fix-attempted=yes }}

Arthur and Bertha

| Arthur is the "left", "black", or "vertical" player, and Bertha is the "right", "white", or "horizontal" player in a combinatorial game. Additionally, Arthur, given the same outcome, prefers a game to take the fewest moves, while Bertha prefers a game to take the most moves.{{Cite book |title=On Numbers and Games |last=Conway |first=John Horton |publisher=CRC Press |year = 2000 |isbn=9781568811277 |pages=71, 175, 176}}

= Physics =

The names Alice and Bob are often used to name the participants in thought experiments in physics.{{Cite web |url=http://physicsworld.com/cws/article/news/2013/apr/16/alice-and-bob-communicate-without-transferring-a-single-photon|title=Alice and Bob communicate without transferring a single photon |website=physicsworld.com |date=16 April 2013 |language=en-GB |access-date=2017-06-19}}{{Cite journal |last1=Frazier |first1=Matthew |last2=Taddese |first2=Biniyam |last3=Antonsen |first3=Thomas |last4=Anlage |first4=Steven M. |date=2013-02-07 |title=Nonlinear Time Reversal in a Wave Chaotic System |journal=Physical Review Letters |language=en-US |volume=110 |issue=6 |pages=063902 |doi=10.1103/physrevlett.110.063902 |pmid=23432243 |arxiv=1207.1667 |bibcode=2013PhRvL.110f3902F|s2cid=35907279 }} More alphabetical names, usually of alternating gender, are used as required, e.g. "Alice and Bob (and Carol and Dick and Eve)".{{Cite web |url=http://www.lassp.cornell.edu/lassp_data/master.pdf |title=209: Notes on Special Relativity |date=5 March 2000 |first=N. |last=David Mermin |author-link=N. David Mermin}} An example with several names.

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, Lucas Lamata, Clarence W. De Silva, Marco B. Quadrelli, [https://arxiv.org/ftp/arxiv/papers/2007/2007.15249.pdf Quantum Teleportation for Control of Dynamic Systems and Autonomy], [https://www.actapress.com/PaperInfo.aspx?paperId=47550 Journal of Mechatronic Systems and Control, Volume 49, Issue 3, pp. 124-131, 2021].{{cite journal |last1=Lamata |first1=Lucas |last2=Quadrelli |first2=Marco B. |last3=de Silva |first3=Clarence W. |last4=Kumar |first4=Prem |last5=Kanter |first5=Gregory S. |last6=Ghazinejad |first6=Maziar |last7=Khoshnoud |first7=Farbod |title=Quantum Mechatronics |journal=Electronics |date=12 October 2021 |volume=10 |issue=20 |pages=2483 |doi=10.3390/electronics10202483 |doi-access=free }} Farbod Khoshnoud, Maziar Ghazinejad, Automated quantum entanglement and cryptography for networks of robotic systems, IEEE/ASME International Conference on Mechatronic and Embedded Systems and Applications (MESA), IDETC-CIE 2021, Virtual Conference: August 17 – 20, DETC2021-71653, 2021.{{cite conference | last1=Khoshnoud | first1=Farbod | last2=Aiello | first2=Clarice | last3=Quadrelli | first3=Bruno | last4=Ghazinejad | first4=Maziar | last5=De Silva | first5=Clarence | last6=Khoshnoud | first6=Farbod | last7=Bahr | first7=Behnam | last8=Lamata | first8=Lucas | title=Modernizing Mechatronics course with Quantum Engineering | publisher=ASEE Conferences | date=23 April 2021 | doi=10.18260/1-2--38241 |url=https://peer.asee.org/38241|conference=2021 ASEE Pacific Southwest Conference - "Pushing Past Pandemic Pedagogy: Learning from Disruption"| doi-access=free }} [https://peer.asee.org/modernizing-mechatronics-course-with-quantum-engineering.pdf PDF]{{cite journal |last1=Khoshnoud |first1=Farbod |last2=Esat |first2=Ibrahim I. |last3=de Silva |first3=Clarence W. |last4=Quadrelli |first4=Marco B. |title=Quantum Network of Cooperative Unmanned Autonomous Systems |journal=Unmanned Systems |date=April 2019 |volume=07 |issue=2 |pages=137–145 |doi=10.1142/S2301385019500055 |s2cid=149842737 |url=https://www.worldscientific.com/doi/abs/10.1142/S2301385019500055 |access-date=7 September 2023 |language=en |issn=2301-3850}}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.

References

{{Reflist|30em|refs=

{{cite book |last=Schneier |first=Bruce |author-link=Bruce Schneier |date=1994 |title=Applied Cryptography: Protocols, Algorithms, and Source Code in C |publisher=Wiley |isbn=978-0-471-59756-8 |page=44 |quote=Mallet can intercept Alice's database inquiry, and substitute his own public key for Alice's. He can do the same to Bob.}}

{{cite book |last=Schneier |first=Bruce |author-link=Bruce Schneier |date=1996 |title=Applied Cryptography: Protocols, Algorithms, and Source Code in C |edition=Second |publisher=Wiley |isbn=978-0-471-11709-4 |page=23 |id=Table 2.1: Dramatis Personae}}

{{cite book |author-link=Charles L. Perkins |first=Charles L. |last=Perkins |display-authors=etal |date=2000 |title=Firewalls: 24seven |publisher=Network Press |isbn=9780782125290 |page=130 |quote=Mallet maintains the illusion that Alice and Bob are talking to each other rather than to him by intercepting the messages and retransmitting them.}}

{{cite book |author-link=Brian LaMacchia |first=Brian |last=LaMacchia |date=2002 |title=.NET Framework Security |publisher=Addison-Wesley |isbn=9780672321849 |page=616 |quote=Mallet represents an active adversary that not only listens to all communications between Alice and Bob but can also modify the contents of any communication he sees while it is in transit.}}

{{cite book |editor-link=Shlomi Dolev |editor-first=Shlomi |editor-last=Dolev |date=2009 |title=Algorithmic Aspects of Wireless Sensor Networks |publisher=Springer |isbn=9783642054334 |page=67 |quote=We model key choices of Alice, Bob and adversary Mallet as independent random variables A, B and M [...]}}

{{cite book |last=Stallings |first=William |author-link=William Stallings |date=1998 |title=Cryptography and Network Security: Principles and Practice |publisher=Pearson |isbn=978-0133354690 |page=317 |quote=Suppose Alice and Bob wish to exchange keys, and Darth is the adversary.}}

}}

External links

[http://cryptocouple.com/ History of Alice and Bob]
[http://people.csail.mit.edu/rivest/Rsapaper.pdf A Method for Obtaining Digital Signatures and Public-Key Cryptosystems] {{Webarchive|url=https://web.archive.org/web/20081217101831/http://people.csail.mit.edu/rivest/Rsapaper.pdf |date=December 17, 2008 }}
[http://downlode.org/Etext/alicebob.html The Alice and Bob After-Dinner Speech], given at the Zurich Seminar, April 1984, by John Gordon
[http://www.catonmat.net/blog/musical-geek-friday-alice-and-bob/ Geek Song: "Alice and Bob"]
[https://web.archive.org/web/20060619074924/http://rogers.phy.bris.ac.uk/denzil/denweb4.html Alice and Bob jokes] (mainly Quantum Computing-related)
[https://web.archive.org/web/20070303030954/http://www.networkworld.com/news/2006/103006-bob.html A short history of Bobs (story and slideshow) in the computing industry, from Alice & Bob to Microsoft Bob and Father of Ethernet Bob Metcalfe]
[https://xkcd.com/177/ XKCD #177: Alice and Bob]

Category:Cryptographic protocols

Category:Placeholder names

Category:Thought experiments in physics

Category:Fictional duos

Category:History of computing