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'''Alice''' and '''Bob''', also just '''A''' and '''B''', are the standard example users in writing on [[cryptography]] and [[coding theory]]. Carol and Dave often join them for protocols that require more than two players.  
'''Alice''' and '''Bob''', also just '''A''' and '''B''', are the standard example users in writing on [[cryptography]], [[coding theory]], communication complexity theory etc. Carol and Dave often join them for protocols that require more than two players.  


{{quotation| The most familiar names in network security are neither vendors nor geeks: Try Alice and Bob.<ref name=networld>{{citation
{{quotation| The most familiar names in network security are neither vendors nor geeks: Try Alice and Bob.<ref name=networld>{{citation
Line 16: Line 16:
  | publisher = John Wiley & Sons
  | publisher = John Wiley & Sons
  |ISBN =0-471-11709-9}} page 23</ref> with two kinds of attacker:
  |ISBN =0-471-11709-9}} page 23</ref> with two kinds of attacker:
* Eve the Eavesdropper, using [[passive attack]]s
* Eve the Eavesdropper, using [[passive attack]]s, just trying to read messages
* Mallory the Malicious, using [[active attack]]s
* Mallory the Malicious, using [[active attack]]s, attempting to deceive A and B by altering messages or sending bogus ones
and several other types of player required in various protocols:
and several other types of player required in various protocols:
* Victor the Verifier
* Victor the Verifier
Line 24: Line 24:
* Walter the Warden, who watches over A and B in some protocols
* Walter the Warden, who watches over A and B in some protocols


Schneier's extensions seem to be in the process of becoming standard as well.
Schneier's extensions seem to be in the process of becoming standard as well. There is even an [http://xkcd.com/177/ XKCD cartoon] with Eve being jealous of Alice over Bob.


It is also moderately common to add additional characters as needed for a particular protocol. For example, in discussing a e-commerce system, one might need Matlida the Merchant and Ivan the Issuer of credentials.
It is also moderately common to add additional characters as needed for a particular protocol. For example, in discussing a e-commerce system, one might need Matlida the Merchant and Ivan the Issuer of credentials.
Line 30: Line 30:
== History ==
== History ==


Alice and Bob were introduced in the original paper <ref>{{citation
Alice and Bob were introduced in the original paper (1978)<ref>{{citation
| author = Rivest, Shamir & Adleman
| author = Rivest, Shamir & Adleman
| url = http://people.csail.mit.edu/rivest/Rsapaper.pdf
| title = A Method for Obtaining Digital Signatures and Public-Key Cryptosystems
| title = A Method for Obtaining Digital Signatures and Public-Key Cryptosystems
| journal = Commun. ACM | volume = 21 | pages = 120-126 ([http://people.csail.mit.edu/rivest/Rsapaper.pdf pdf])
| date = 1978}}</ref>
| date = 1978}}</ref>
on the [[RSA algorithm]] for [[public key]] cryptography.
on the [[RSA algorithm]] for [[public key]] cryptography.
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{{quotation|Rivest ... says he came up with Alice and Bob to be able to use "A" and "B" for notation, and that by having one male and one female, the pronouns "he" and "she" could be used in descriptions. Rivest says it is possible that Alice came to mind because he is something of an Alice in Wonderland buff.<ref name=networld />}}
{{quotation|Rivest ... says he came up with Alice and Bob to be able to use "A" and "B" for notation, and that by having one male and one female, the pronouns "he" and "she" could be used in descriptions. Rivest says it is possible that Alice came to mind because he is something of an Alice in Wonderland buff.<ref name=networld />}}


The similar name of the film [[Bob & Carol & Ted & Alice]] and subsequent TV show appears to be just a coincidence.
The similar name of the film [[Bob & Carol & Ted & Alice]] and subsequent TV show appears to be just a coincidence. Rivest denies that there is a connection.


Alice and Bob have an amusing biography on the web.
Alice and Bob have an amusing biography on the web.
Line 60: Line 60:
While Alice and Bob are standard in cryptography and coding theory, other pairs of players are used in other domains.
While Alice and Bob are standard in cryptography and coding theory, other pairs of players are used in other domains.


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.
'''Arthur''' and '''Merlin''' were introduced by László Babai (1985)<ref>
László Babai, ''Trading group theory for randomness''.
STOC '85 Proceedings of the seventeenth annual ACM symposium on Theory of computing, ACM. 421–429 (1985),
([http://dl.acm.org/citation.cfm?id=22192 abstract])
</ref>.
This pair is used in [[computational complexity theory]] for [[interactive proof system]]s:
Merlin, the wizard, is the nondeterministic player (with unbounded computational power)
who wants to convince the random player Arthur of the truth of a statement.


In [[combinatorial game theory]], the characters are often '''Paul''' and '''Carole'''. The characters were introduced in the solution of the [[Twenty Questions]] problem,<ref>{{citation |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 | pages=81–93}}</ref> 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 games in the roles of Pusher and Chooser respectively, and have since been used in various roles.<ref>{{citation |last=Muthukrishnan|first=S. | title=Data Streams: Algorithms and Applications | isbn=9781933019147 | publisher=[http://books.google.com/books?id=415loiMd_c0C&pg=PA2&dq=%22paul+and+carole%22 Now Publishers] | year=2005 | url=http://algo.research.googlepages.com/eight.ps | page=3}}</ref>
'''Paul''' (the Pusher) and '''Carole''' (the Chooser) were introduced by Joel Spencer and Peter Winkler (1992)<ref>
{{citation |last1=Spencer|first1=Joel|author1-link=Joel Spencer | last2=Winkler|first2=Peter|author2-link=Peter Winkler | title=Three Thresholds for a Liar | journal=Combinatorics, Probability and Computing | year=1992 | volume=1 | pages=81–93 ([http://math.dartmouth.edu/~pw/papers/3thresh.ps Postscript])}}</ref>
in their study of the [[Twenty Questions]] game (with lies) where Paul asks the questions and Carole answers them.
In this pair "Paul" refers to Pál (=Paul) [[Pál Erdős|Erdős]], and "Carole" is an [[anagram]] of "oracle".
Since then these names have been used for various similar roles in [[combinatorial game theory]].


In English grammar discussions, John and Mary are often used.
In English grammar discussions, notably in [[Noam Chomsky]]'s writings, '''John''' and '''Mary''' are often used.


==References==
==References==
{{reflist|2}}
{{reflist|2}}

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Alice and Bob, also just A and B, are the standard example users in writing on cryptography, coding theory, communication complexity theory etc. Carol and Dave often join them for protocols that require more than two players.

The most familiar names in network security are neither vendors nor geeks: Try Alice and Bob.[1]

Bruce Schneier extends these [2] with two kinds of attacker:

  • Eve the Eavesdropper, using passive attacks, just trying to read messages
  • Mallory the Malicious, using active attacks, attempting to deceive A and B by altering messages or sending bogus ones

and several other types of player required in various protocols:

  • Victor the Verifier
  • Peggy the Prover
  • Trent the Trusted third party
  • Walter the Warden, who watches over A and B in some protocols

Schneier's extensions seem to be in the process of becoming standard as well. There is even an XKCD cartoon with Eve being jealous of Alice over Bob.

It is also moderately common to add additional characters as needed for a particular protocol. For example, in discussing a e-commerce system, one might need Matlida the Merchant and Ivan the Issuer of credentials.

History

Alice and Bob were introduced in the original paper (1978)[3] on the RSA algorithm for public key cryptography.

Rivest ... says he came up with Alice and Bob to be able to use "A" and "B" for notation, and that by having one male and one female, the pronouns "he" and "she" could be used in descriptions. Rivest says it is possible that Alice came to mind because he is something of an Alice in Wonderland buff.[1]

The similar name of the film Bob & Carol & Ted & Alice and subsequent TV show appears to be just a coincidence. Rivest denies that there is a connection.

Alice and Bob have an amusing biography on the web.

Now there are hundreds of papers written about Alice and Bob. Over the years Alice and Bob have tried to defraud insurance companies, they've played poker for high stakes by mail, and they've exchanged secret messages over tapped telephones.

If we put together snippets from lots of papers, we get a fascinating picture of their lives. This may be the first time a definitive biography of Alice and Bob has been given. ...

Against all odds, over a noisy telephone line, tapped by the tax authorities and the secret police, Alice will happily attempt, with someone she doesn't trust, whom she cannot hear clearly, and who is probably someone else, to fiddle her tax returns and to organise a coup d'etat, while at the same time minimising the cost of the phone call.

A coding theorist is someone who doesn't think Alice is crazy.[4]

Other pairs

While Alice and Bob are standard in cryptography and coding theory, other pairs of players are used in other domains.

Arthur and Merlin were introduced by László Babai (1985)[5]. This pair is used in computational complexity theory for interactive proof systems: Merlin, the wizard, is the nondeterministic player (with unbounded computational power) who wants to convince the random player Arthur of the truth of a statement.

Paul (the Pusher) and Carole (the Chooser) were introduced by Joel Spencer and Peter Winkler (1992)[6] in their study of the Twenty Questions game (with lies) where Paul asks the questions and Carole answers them. In this pair "Paul" refers to Pál (=Paul) Erdős, and "Carole" is an anagram of "oracle". Since then these names have been used for various similar roles in combinatorial game theory.

In English grammar discussions, notably in Noam Chomsky's writings, John and Mary are often used.

References

  1. 1.0 1.1 "Security's inseparable couple", Network World, Feb 2005
  2. Schneier, Bruce (2nd edition, 1996,), Applied Cryptography, John Wiley & Sons, ISBN 0-471-11709-9 page 23
  3. Rivest, Shamir & Adleman (1978), "A Method for Obtaining Digital Signatures and Public-Key Cryptosystems", Commun. ACM 21: 120-126 (pdf)
  4. John Gordon (1984), The Story of Alice and Bob
  5. László Babai, Trading group theory for randomness. STOC '85 Proceedings of the seventeenth annual ACM symposium on Theory of computing, ACM. 421–429 (1985), (abstract)
  6. Spencer, Joel & Peter Winkler (1992), "Three Thresholds for a Liar", Combinatorics, Probability and Computing 1: 81–93 (Postscript)