Secret Codes Poster Elements
Photo and Image Credits and Permissions
 Image of picture code from 1948 Bear Cub Handbook, available at http://www.papergreat.com/2012/03/neatillustrations-and-more-from-1948.html.
 Image of Caesar Cipher shift by Matt_Crypto, available at http://en.wikipedia.org/wiki/Caesar_cipher, released to
public domain.
 Photo of fire engine siren by David R. Tribble, available from http://en.wikipedia.org/wiki/Siren_(noisemaker), used
with permission.
 Photo of scytale by Luringen, available from http://en.wikipedia.org/wiki/Scytale, used with permission.
 Image of Morse Code by Rhey T. Snodgrass & Victor F. Camp, available from
http://en.wikipedia.org/wiki/Morse_code, in public domain.
 Photo of enigma machine by Karsten Sperling, available from http://en.wikipedia.org/wiki/Enigma_machine, released
to public domain.
 Image of Paul Revere’s midnight ride, from U.S. National Archives, available from
http://en.wikipedia.org/wiki/Paul_Revere, in public domain.
 Photo of civil war signal corps kit by Pablo Jimenez-Reyes, United States Army Historical Collection, available from
http://en.wikipedia.org/wiki/Signal_Corps_in_the_American_Civil_War, in public domain.
Picture Ciphers
From the 1948 Bear Cub Handbook!
Caesar Ciphers
One of the oldest ciphers is named
after Julius Caesar. In a Caesar
cipher, the alphabet is shifted a
certain number of places and each
letter in the message is replaced by
the corresponding shifted letter.
What is a Code?
A code is any symbol or signal used to stand for or
communicate something.
To communicate
To communicate
To communicate
we use the code DOG
We
surrender!
coming
we use the code
we use the code
What is a Cipher?
A cipher is a particular type of secret code
that changes each letter of a message into
another letter or symbol.
The real message is called the plaintext.
The coded message is called the ciphertext.
The system of rules that describes how the
plaintext letters and ciphertext letters are
related is called the key.
What is Cryptography?
Cryptography is the mathematics and
science of secret messages.
Cryptographers do three kinds of activities.
 They change messages into secret
messages, which is called encryption.
 They change secret messages back into
original messages, which is called
decryption.
 They figure out keys to codes and ciphers,
which is called code breaking.
Secret Codes in History
In April of 1775 in Boston, Paul Revere used
a very simple code to send a message to
Charleston about how the British were
coming.
The code involved the number of lanterns
hung in the tower of the Old North Church:
“One if by land, two if by sea.”
Scytale Ciphers
A scytale (SKEE-tay-LEE) is a simple cipher machine
consisting of a wooden staff with a strip of parchment
wound around it on which is written a message. The
ancient Spartans are said to have used this cipher to
communicate during military campaigns. The recipient
uses a staff of the same diameter on which he wraps
the parchment to read the message. It has the
advantage of being fast and
not prone to mistakes—a
necessary property when on
the battlefield.
Secret Codes
Morse Code
Morse code transmits letters as a series
of on-off tones, lights, or clicks that can
be interpreted by a skilled listener or
observer.
Secret Codes in History
During World War II, the Germans
developed the ENIGMA, an encryption
device to send secret messages. It
was the most secure and complex
cipher system ever built at the time.
It took a long time for the U.S. to
discover the key.
NATO Phonetic Alphabet
This code replaces each letter with a word that
begins with that letter. The replacement words are
easy to tell apart from one another when spoken.
This is a spoken code and is good for two-way radio
communication, when static often makes it difficult to
tell two similar sounding letters, like B and D, apart.
Alpha
Bravo
Charlie
Delta
Echo
Foxtrot
Golf
Hotel
India
Juliett
Kilo
Lima
Mike
November
Oscar
Papa
Quebec
Romeo
Sierra
Tango
Uniform
Victor
Whiskey
X-ray
Yankee
Zulu
Secret Codes in History
During the Civil War, both the
Union and Confederate armies
developed Signal Corps for the
purpose of sending and
receiving secret messages.
They waved red and white flags
from hills, towers, and roofs to
send their messages. The patterns of waves, called wigs and
wags, revealed the letters of the message. Since the flags
could be seen by both armies, messages were encrypted with
a cipher disk before being sent.