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Or perhaps you remember using special symbols to write notes to your "squeeze" in class.
If the note was intercepted , your teacher, could learn nothing about your romance.
In more serious uses, codes and ciphers are used by our military and diplomatic forces to keep confidential information from unauthorized eyes.
Businesses also send data that has been encoded to try and protect trade secrets and back-room deals.
To get a feel for these methods, let's take a look at some ciphers. (Actually, substitution ciphers could properly be called codes in most cases.) Morse code, shorthand, semaphore, and the ASCII code with which these characters are being stored in inside my Macintosh are all examples.
(ASCII stands for American Standard Code for Information Interchange, just in case you're interested.) The only difference between these and the spy codes is that the above examples are standardized so that everybody knows them.
Ciphers are broken into two main categories; substitution ciphers and transposition ciphers.
If you don't know Greek (and not many of us do) the above letters could be a form of code themselves!
Although the distinction is fuzzy, ciphers are different from codes.
By way of analogy, to get into your home you would put a key in a lock to open the door.
This process (the use of a key and a lock) is the method or algorithm.Substitution ciphers replace letters in the plaintext with other letters or symbols, keeping the order in which the symbols fall the same.