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Substitution Ciphers: Do you have what it takes?

Fun Fact Icon Educated people in North America, even before the United States was established, used cryptographic systems for their personal mail, since the postal system in the colonial period often was unreliable and letters might go astray.


You can use cryptography to add another layer of protection to your email messages! Learn how to communicate using monoalphabetic cipher and solve our email crypto challenge!

How to communicate in code

Materials: Pencil and a sheet of paper (lined paper best).

  1. On the left side of a sheet of paper, starting at the top, write the letter "A" and below it on the second line, write the letter "B" and underneath on the third line, write the letter "C". Continue until you have written all the letters of the alphabet down the left side of your sheet of paper.

  2. Select a number between 3 and 10. For this example, we will use the number 5.

  3. Count down 5 lines on your sheet of paper and you will find the letter "E". To the right of the letter "E", write the first letter of the alphabet, "A". Go down one more line (F) and next to "F", write the letter "B". Go down to "G" and write the letter "C". Next, go to the letter "H" and write in the letter "D" to its right. Continue this until you run out of letters.

  4. If you did this correctly, you will see something like this, although the entire code (or cipher) is not written out here.

    • A  W
    • B  X
    • C  Y
    • D  Z
    • E  A
    • F  B
    • G  C
    • H  D
    • I  E
    • J  F
    • K  G

Now use the code:

You checked your email this evening and saw a message from your friend. Using the number 5 as the key, decrypt your friend's message:
IAAP IA WP PDA OYDKKH BHWC LKHA PKIKNNKS WP 7:00.
MEET ME AT THE SCHOOL FLAG POLE TOMORROW AT 7:00.
What did you write back to your friend?
  1. E SEHH ZBDG
    I WILL DFHK
  2. OAA UKQ PDAJ
    SEE YOU THEN
  3. JKPN
    NOTR
  4. E ZK JKP HERA DANA
    I DO NOT LIVE HERE

Show Solutions

Solution: B (See you then)

Photograph of Enigma MachineWant to learn more?

The Enigma is an example of a mechanical implementation of a polyalphabetic substitution cipher. The Enigma is on display at the National Cryptologic Museum. Check it out!

Date Posted: Jul 25, 2012 | Last Modified: Jul 25, 2012 | Last Reviewed: Jul 25, 2012

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