# Cryptography 101

• By Melissa Salpietra
• Posted 07.01.07
• NOVA scienceNOW

You can make a message secret in countless different ways. One common way is to use a substitution cipher, in which one letter is substituted for another. Another is to employ a transposition cipher, in which the letters change position within the message. In this interactive, explore examples of a substitution cipher and two kinds of transposition cipher.

Learn different ways to make a message secret.

## Credits

(Kryptos)

• ### Kryptos

A coded sculpture at CIA headquarters has yet to be fully broken.

• ### Kryptos: Expert Q&A

James Sanborn, creator of the Kryptos puzzle, answers questions about making—and breaking—codes.

• ### Twin Prime Conjecture

New insight into a 2,300-year-old mystery surrounding prime numbers inspires a song.

• ### Seven Prime Questions

In this audio interactive, five mathematicians explain what primes are, what the twin prime conjecture is, and more.

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