## Applied Kid Cryptography

``Where's Waldo?'' is
a puzzle book where each page contains a very detailed picture with many
different characters (click here for
``Where's Waldo?'' on the WEB). The goal is to find Waldo, a predefined
character . As the
following true story will reveal, in these pictures also lies an interesting
cryptographic problem.

Our story involves two characters; for the sake of anonymity
and following a long cryptographic tradition we shall call them Alice and
Bob. One day, while Alice and Bob were playing ``Where's Waldo?'', Alice
suddenly claimed: *``I know where Waldo is!''.* Bob responded with
a baffling riddle: *``Alice, do you know what a liar is?''*. Worried
about her reputation (both as an honest person and as a qualified cryptographer),
Alice wondered: *``How can I prove to Bob that I know where Waldo is
without revealing his location?*''

Can you help Alice and propose a simple solution that
does not require complex computation and is low-tech in terms of the required
resources?

Click here for discussion
and pointers to solutions.

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