Alice and Bob

Yash Soni / May 10, 2020
2 min read

XKCD

Alice and Bob are fictional characters commonly used as a placeholder name in cryptology.

Alice and Bob first appeared in 1978 in a paper on cryptography. 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".

Instead of saying "How can B send a private message M to A in a public-key cryptosystem?", they chose to represent it with more human friendly names Alice and Bob.

Within a few years, reference to Alice and Bob in cryptological literature became failry common and it even started to appear in Science and Engineering.

Cast of characters#

The world of Alice and Bob grew with time and now there is a complete cast of characters serving some generic purpose.

character nameusage    
Alice and BobThe original, generic characters. Generally, Alice and Bob want to exchange a message or cryptographic key.
CarolThe generic third participant.
EveThe eavesdropper, who is usually a passive attacker
GraceA government representative
MalloryMalicious attacker. Unlike the passive Eve, Mallory/Mallet is an active attacker. usually participating in man-in-middle attacks
TrentA trusted arbitrator, who acts as a neutral third party

XKCD
Physics though experiment


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