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NOVA scienceNOW: Kryptos

Viewing Ideas

Before Watching

1. Define "code" and brainstorm some acronyms and abbreviations, which are simple codes. Have students describe different types of codes they have created or solved (e.g. text messages or ciphers in books). Ask what a code is and why codes are used. (A code is a system of symbols, letters, words, or signals used in place of words or numbers to either store information or convey a message. They are used to make short or secret messages.) Acronyms are one type of code and are usually words formed from the first letters of other words (e.g. PIN=personal identification number; radar=radio detecting and ranging). In general, acronyms are pronounced as a word. Abbreviations are another type of code (e.g., HS=high school; MS=middle school; Y2K=Year 2000; ATM=automated teller machine.) Have students brainstorm some familiar acronyms and abbreviations and tell what each stands for.

2. Introduce cipher terminology. In a cipher, the replaced symbols, often letters, follow a rule that is defined by a key and known only by the sender and receiver of the cipher. To introduce students to the terms plaintext, cipher, and key, write the following example on the board and explain how each term applies to a secret message.

   • The message is called the plaintext because it is the unchanged source information. Example: The cat ran away.

   • The secret message generated is called a cipher or ciphertext and it is the encrypted form of the plaintext. Example: Uif dbu sbo bxbz.

   • The key is the secret solution technique. Example: Each letter of the plaintext is replaced by the letter that comes after it in the alphabet.

   After reviewing the terms with students, write a different one-line cipher on the board, using the above key, for the class to solve.

3. Write substitution and transposition ciphers. Provide students with definitions and examples of the two main cipher systems described below. Then have pairs write one transposition and one substitution cipher.

   • To write a substitution cipher, replace the plaintext with other symbols without changing the sequence.

     Plaintext: The dog is under the desk.

     Substitution cipher: 20 8 5 4 15 7 9 19 21 14 4 5 18 20 8 5 4 5 19 11.

     Key: Ordered numbers 1–26 replace letters of the alphabet.

   • To write a transposition, retain all the plaintext symbols, but change the order in which they occur.

     Plaintext: THE MESSAGE IS HIDDEN

     Transposition cipher: TEESGIHDEHMSAESIDN

     Key (directions): Write the letters, in order, in a grid alternating between the first and second row.

     T	E	E	S	G	I	H	D	E
     H	M	S	A	E	S	I	D	N

     Next, write the letters in the first row of the grid, in order, followed by the letters in the second row of the grid.

     Have pairs post their ciphers in the classroom for other students to solve.

4. Make invisible ink and use it to write a message. There are many ways to conceal a message. One method involves using "invisible" ink to write the message and a chemical process to reveal the writing. Have pairs of students make "invisible" ink by mixing one tablespoon baking soda with one tablespoon water. Next, have them fold a piece of copier paper into thirds and then write a brief message, using a cotton swab, on each of the three sections. Let the paper dry. Ask students to test which type of juice best reveals the message—grape juice, grape juice concentrate, or cranberry juice. To test the different juices, have pairs dip a thin paint brush in the juice to be tested and then gently "paint" over the invisible message. Have them research and explain how their messages were revealed. (Different juices contain different chemicals including flavenoid pigments which give each juice its color. When the flavenoid pigments interact with the baking soda, they change form and appear blue. Baking soda is basic; most juices are acidic. An acid-base reaction occurs with the baking soda and the juice, revealing the writing. The amount of pigment available also influences how dark the message becomes.)

After Watching

1. Write a message using Julius Caesar's substitution code. The segment describes how Julius Caesar (100–44 BCE) used codes and ciphers so that an enemy could not understand the messages he sent to his troops. The substitution code he used shifted the position of alphabet letters three places.

   Write on the board the following alphabet and substitution key:

   A

   B

   C

   D

   E

   F

   G

   H

   I

   J

   K

   L

   M

   N

   O

   P

   Q

   R

   S

   T

   U

   V

   W

   X

   Y

   Z

   X

   Y

   Z

   A

   B

   C

   D

   E

   F

   G

   H

   I

   J

   K

   L

   M

   N

   O

   P

   Q

   R

   S

   T

   U

   V

   W

   Have pairs find an interesting fact about the Roman Empire at

   www.pbs.org/empires/romans/

   and write a brief statement about it.

   Then have them write their fact using Julius Caesar's substitution code.

   Group students by asking two or three sets of pairs to work together to decipher each other's Roman Empire facts.

2. Make a substitution-code disc. Divide the class into groups and have each one make a code disc. Give groups two white paper plates, and have students cut away the outer rim from one of the plates. Ask groups to make a code disc by centering the smaller plate on top of the larger plate and then use a brass fastener to join both at the center. Have students write the alphabet around the rim of the larger plate and a second set of symbols (of their choice) on the smaller plate near its rim directly beneath the letters on the larger plate. Make sure there is a one-to-one correspondence between the markings on the two plates.

   Possible code sets:

   • two sets of the alphabet
   • one alphabet, one 1–26 number set
   • one alphabet, one set of symbols

   On a separate piece of paper, have groups write the name of a favorite musician and/or band and a sentence about why they like the musician(s) they chose. (This original message is the plaintext.) Then have groups turn the smaller disc, realigning it with the outer alphabet. Ask groups to then write their band description using substitution. (The new message is the cipher.) Have each group define their key and then exchange their cipher with another group to see which group can first "crack" their cipher.

3. Design and display a poster about a code system. Divide the class into groups and assign each group one of the code methods listed below. Then have them research their assigned code system and present their work in a poster for display. Groups should write a sample cipher for the rest of the class to crack.

   • Playfair cipher: a substitution code invented by seventeenth-century scientist, Sir Charles Wheatstone.

   • Vigenère Table: a substitution code invented by sixteenth-century cryptologist, Blaise de Vigenère.

   • Transposition ciphers: Frequently used early in the history of cryptography and still popular today

   • Product ciphers: Used by the German army during World War 1

   (Suggest as a resource: www.ridex.co.uk/cryptography/)

4. Make a model similar to Kryptos that has a concealed riddle. Once Kryptos has been deciphered, the meaning of the messages may form a riddle that still need to be solved.

   In this activity, groups will write ciphers of riddle poems for other students to decipher and then solve.

   To review riddle poems, write the following poem on the board for the class to solve:

   The beginning of eternity,
   The end of time and space,
   The beginning of every end,
   And the end of every place.
   -The Guess Book (c. 1820)

   (solution: the letter e)

   Next, divide the class into teams. Have each team write a riddle or riddle poem. Have them decide on a key and then make a cipher of their riddle. Provide teams with scissors and poster board and have them write their cipher riddle poem on, or cut it out of, their poster board. Display student work and have classmates try to decipher and solve hidden riddles.

   [For additional riddle poems, see the suggested resource in the Links and Books section.]

Web Sites

NOVA scienceNOW
www.pbs.org/nova/sciencenow/3411/03.html
Offers Kryptos-related resources and activities including "Cryptography 101" and "Send a Secret Message", streamed video, and the opportunity to ask questions to artist Jim Sanborn.

Codes and Ciphers
www.otr.com/ciphers.shtml
Includes information about the history of codes and code breaking.

Kryptos Links
www.elonka.com/kryptos/
Contains several links for articles, interviews, and books related to Kryptos.

Kryptos, The Da Vinci Code, The Solomon Key
www.kryptos-cia.com/
Tracks the progress and success in cracking three parts of Kryptos.

Script for Writing a Riddle Poem
www.readwritethink.org/lesson_images/lesson169/WriteARiddle.pdf
Provides directions for writing riddle poems.

The Secret Language
www.exploratorium.edu/ronh/secret/secret.html
Describes substitution and transposition codes and includes several examples.

Books

Cryptography: The Science of Secret Writing
by Laurence Dwight Smith. Dover, 1955.
Introduces students to codes and the history of codes and ciphers.

Top Secret: A Handbook of Codes, Ciphers, and Secret Writing
by Paul B. Janeczko (editor) and Jenna Lareau (illustrator). Candlewick Press, 2006.
Explains secret writing and includes decoding exercises.