1 . Secret codes (密码) keep messages private. Banks, companies, and government agencies use secret codes in doing business, especially when information is sent by computer.
People have used secret codes for thousands of years.
There are three main types of cryptography.
A code uses symbols to replace words, phrases, or sentences. To read the message of a real code, you must have a code book.
A.It is very hard to break a code without the code book. |
B.In any language, some letters are used more than others. |
C.Only people who know the keyword can read the message. |
D.As long as there have been codes, people have tried to break them. |
E.You can hide a message by having the first letters of each word spell it out. |
F.With a code book, you might write down words that would stand for other words. |
G.Another way to hide a message is to use symbols to stand for specific letters of the alphabet. |