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Sunday, 6 January 2013
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.
Let’s 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.
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 don’t 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, “bridge” might 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. 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 computer’s 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.
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