Upload
vampire459
View
220
Download
0
Embed Size (px)
Citation preview
7/28/2019 Secret Codes Keep Messages Private
1/3
Secret codes keep messages private. Codes are very useful for sending secret military information during
wartime. Banks, companies, and government agencies also use secret codes in doing business, especially
when information is sent by computer.
People have used secret codes for thousands of years. As long as there have been codes, people have
tried to break them. Code breaking never lags far behind code making.
HIDDEN WRITING
The science of creating and reading coded messages is called cryptography (pronounced krip-TOG-ruh-
fee). The word means hidden writing.
There are three main types of hidden writing. They are concealed messages, ciphers, and codes.
However, all three are commonly called codes.
CONCEALED MESSAGES
You can conceal (hide) a message by having the first letters of each word spell it out. For example, the
first letters of My elephant eats too many eels, spell out the hidden message Meet me.
Concealed messages, like this one, are easy to break. Once the secret is out, anyone can read them.
CODES CALLED CIPHERS
Another way to hide a message is to use symbols to stand for specific letters of the alphabet. You might
represent each letter with a number, for example. Although we call this a code, experts call it a cipher.
Lets number the letters of the alphabet, in order, from 1 to 26. If we substitute a number for each
letter, the message Meet me would read 13 5 5 20 13 5. This is called a substitution cipher.
7/28/2019 Secret Codes Keep Messages Private
2/3
In a transposition cipher, the letters in a message are rearranged in some way. We could, for example,
reverse each pair of letters in Meet me. Then our message would read Emte em.
CODES AND CODEBOOKS
A code uses symbols to replace words, phrases, or sentences. To read the message of a real code, you
must have a code book. However, to work out the cipher above, you dont need a code book. All you
need to know is the system used for substitution or rearrangement.
With a code book, you might write down words that would stand for other words. For example, bridgemight stand for meet and out might stand for me. The message Bridge out would actually mean
Meet me.
It is very hard to break a code without the code book. However, it is also hard to keep a code book
secret for long. So codes must be changed frequently.
CODE BREAKING
Ciphers are easy to use and remember. A simple cipher, however, is also easy to break. In any language,
some letters are used more than others. In English, e is the most common letter, followed by t and a.
Some letters frequently occur together, such as th and ch. By studying several messages, a code breaker
can easily figure out a simple cipher.
Complex ciphers use a different cipher, or code, for each letter in a message. The letters in a keyword
reveal which cipher is used for each letter. Only people who know the keyword can read the message.
Codes can be almost unbreakable if they use combinations of ciphers and change the keyword often.
During World War II (1939-1945), math experts in Britain broke the German military code. Britain was at
war with Germany. German military forces coded messages with a device called an Enigma machine.
7/28/2019 Secret Codes Keep Messages Private
3/3
Enigma used gears and wheels to create millions of different ciphers. But British mathematicians and
code breakers figured out the cipher and uncovered German military plans.
COMPUTERS AND CODES
Computers can create ciphers many thousands of times more complex than the Enigma machine could.
Computer scientists develop complicated formulas for coding messages. They use keywords that are
long strings of symbols. The computers speed and power creates messages that are very hard to break.
But powerful computers can be used to break codes, too. Any code that can be made can also be
broken.
Also in Encarta Kids
All articles about reading and writing
Language
Writing and Alphabet
On the Web
Visit this virtual exhibit to find out more about the Enigma machine.
Microsoft Encarta 2009. 1993-2008 Microsoft Corporation. All rights reserved.