NOVA Online | Secrets, Lies, and Atomic Spies

Decipher a Coded Message

Shockwave required

Decipher a Coded Message
by Rick Groleau

You could do worse than to confuse the meanings of "code" and "cipher"—even cryptographers sometime use the terms as though they had the same meaning. There is, however, a definite distinction between the two. Codes are letter combinations or symbols used to represent words or concepts. A "10-4" heard over a police radio means "affirmative," for example; and three dots, three dashes, and three dots (...---...) in Morse code stands for the distress message "SOS."

A cipher, on the other hand, is a message in which letters or symbols replace the actual letters in the message. Every cipher has a "key"—information used to decipher a message. Some ciphers have simple keys, others, complex ones. The key for a cipher used by Augustus Caesar, some 2,000 years ago, was simple enough: The receiver just had to shift the alphabet one position. In other words, "a" was represented by "b," "b" was represented by "c," and so on. (Bo fbtz djqifs up csfbl!)

How easy is it to crack a simple cipher? This feature lets you find out. On the following page is a secret message encrypted using a cipher. The cipher's key is straightforward—each letter of the alphabet is represented by another letter. Are you ready to decipher? Then let's get to work!

    Decipher a Coded Message
        requires the Shockwave plug-in

    Decipher a Coded Message
        non-Shockwave version

Shockwave is a plug-in that allows for increased interactivity. If you can see the animated boxes at left, the plugin is already installed. If you do not see the boxes, you can install the Shockwave plugin.

Rick Groleau is managing editor of NOVA Online.

A slightly different version of this feature appeared on NOVA's "Decoding Nazi Secrets" Web site, www.pbs.org/nova/decoding/.

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