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NOVA scienceNOW: Kryptos
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Viewing Ideas
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Before Watching
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. 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.
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.
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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.
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
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:
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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.
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.
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/)
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.
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