Begin the lesson by discussing different types of encryption. Ask the students to give examples of codes they may have encountered.
Create a systematic way of deciphering a code. Begin with the example of Sherlock Holmes' Adventure of the Dancing Men. Ask the students how they would go about deciphering these notes written between two characters in a Sherlock Holmes story. Discuss alphabet frequencies. Have the students find the most common figure used in the puzzle. This figure most likely represents an "E". The frequency of letters is usually E-T-A-O-I-N.
Use Decode de Code to determine other clues to look for when deciphering a code: punctuation, short words, double letters.
Demonstrate the difference between a rotated alphabet code and a random alphabet code using Decode de Code.
Show the students how a rotated alphabet code could be defined by a mathematical equation.
Example: given a code where the alphabet is rotated 5 spaces and A=0, B=1, C=2 and so on
A => F D => I
B => G E => J
C => H F => K
X = the original letter
Y = the encoded letter
X + 5 = Y
So, "HI" becomes "LM"
since H = 7
7 + 5 = 12
and 12 = L
Use Caesar's Cipher to encode messages using an algorithm such as that explained above. Also demonstrate the use of a multiplier instead of a constant as an encryption method.
Allow students time to practice their skills at decoding messages by using Caesar's Cipher II.
Discuss anagrams as a type of code where the letters are re-ordered to make new words. An example of this is the movie title "Con Bites Male Flesh". This is an anagram for "Silence of the Lambs". Have the students try to make anagrams of their own names. They may want to use an anagram finder.