Alice has two secret documents, X and Y. She agrees to let Bob choose and receive one—but only one. Bob, however, doesn’t want Alice to know which document he has selected. So they engage in an exchange of the utmost delicacy…
Alice and Bob in action
This may sound like the introduction to an intellectual thriller novel. Minus a florid touch or two, though, it wouldn’t be out of place in a scientific paper on cryptology. In fact, for slide presentations in the field, a diagram of Alice and Bob’s latest predicament is pretty much de rigeur.
Alice and Bob, you see, are the cryptology’s stock characters, charged with illustrating problems in simple, intuitively appealing stories. (The story above captures a cryptographic concept called “oblivious transfer.”) Their dramas take place in an intimate community of strong personalities. In cryptologists’ stories, Alice and Bob rub shoulders with dramatis personae like these:
- Eve the Eavesdropper, a perennially nosy neighbor;
- Trent, the Trusted Third Party, a universal confidant;
- Mallory, crucible of devious malice (sometimes simply called “The Adversary”);
- Carol, David, and Fawn: Friends called in when Alice and Bob’s tête-à-têtes become lonely.
Alice and Bob are (generally) not a couple. The complex, artificial tensions in their relationships and their games of information withholding, though, have a romantic-comedy quality that hints at unacknowledged longings.
Alice and Bob were introduced in a scientific paper in 1978 as a simple, clever way to render the abstract science of cryptology more concrete and give it a folksy, accessible tone. (Incidentally, this paper, entitled “A method for obtaining digital signatures and public-key cryptosystems,” by Rivest, Shamir, and Adleman, also contributed a cryptosystem called RSA.) The duo has had a lasting and influential career. Cryptographers are grateful to Alice and Bob for the islands of clarity they have brought to a science often befogged by complexity. The comic touch doesn’t hurt either.*
* An example of the need: A colleague and I once cited a recipe from the Joy of Cooking in a scientific paper. An anonymous reviewer was scandalized, and instructed us to remove the citation. (We didn’t.)