The Alberti Cipher Wheel
By Clayton

In 1466, an Italian man named Leon Battista Alberti invented the Alberti Cipher Wheel.  It was the first simple substitution cipher machine ever made.  Alberti’s invention speeded up the time needed to cipher and decipher codes.  The danger of the cipher wheel is that it could fall into the hands of an enemy.

How to Make an Alberti Cipher Wheel

1.   Take two sheets of poster board or cardboard.

2.    Cut out two circles. Make one circle about two inches bigger in diameter than the other circle.  

3.   Use a ruler to evenly divide the larger circle into 26 sections.  To do this, draw a line dividing the circle into halves. Put a dot in the center of the line. To divide your circle into exactly 26 sections, use a compass.  Each section should have an angle of 13.8 degrees.  

4.  Put the smaller circle in the center of the larger circle.

5.  Take a paper fastener and stick it through the center of the two circles.  

6.   Use a ruler to draw lines to divide the smaller circle into 26 sections.  To do this, simply match up the lines to the larger circle.

7.    Write the alphabet (in order) around the edges of both circles.

How to Use a Cipher Wheel

1.   The person who is sending the message and the person receiving the message need to use the same letter to create the code.

2.   If you and your friend choose the letter "y," the person creating the message turns the smaller circle until the "y" is aligned to the "a" on the outer circle.  So now the letter "b" becomes a "d" and so on. The person writing the message finds the letters on the small circle and then writes the matching letter from the large circle.

3.  The person who receives the message reads it differently.  The receiver also turns the smaller circle until the "y" is aligned to the "a" on the outer circle. But the receiver decodes the message by finding the letters on the large circle and then writing the matching letter from the small circle.

Other Tips

On the smaller circle write anything that you would like. You could write 26 numbers, symbols, or the alphabet all jumbled up. Just make sure you align it with the letters on the larger wheel.

Citations

Books

Hill, Labin Carrick. Spy’s survival handbook. New York: Scholastic and Tangerine Press, 2003.

Weller, Janet. Hello Out There! Messages in Code. Belgium: Franklin Watts,  1998.   

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