Coding and Decoding Messages

Naturally, an important message has to be so disguised that only a few trusted persons could read it. Messages that are written in a concealed manner are said to be in code, and the process of reading coded messages is known as decoding. In order to decode a message the secret of its arrangement or the key of the code must be known. This is the same key which is used by a person when he translated his message into a coded one.

Generally, the key of a code is a secret which is closely guarded by the sender as well as the recipient of the coded message.

There are many reasons why people sent messages in concealed forms. In some cases the reason may be quite legitimate, in other cases sinister. Coded message may be used by spies to transmit reports to their employers or by criminals and plotters to communicate with their accomplices. On the other hand, governments use secret codes for communication between their legal agents so the message may be read only by those for whom they are intended. Armies and navies of all countries have secret codes. Telegraph companies are known to use special codes for transmitting commercial messages in order to save money; their codes are not secret and may be obtained or inspected in any office of these companies.

There are many methods for writing coded messages. Some of them are very simple and may be easily decoded. Others have now become extremely complex. The entire secret of a coded message lies in the manner an intelligible message is rewritten so that it becomes unintelligible. If the correct instructions for coding and decoding are available, deciphering may prove comparatively simple. But if the code key is not known, even a specialist may be baffled for a clue. Should the key be discovered, however, the entire code naturally becomes valueless. Because of this danger of discovery, governments are continually revising their codes.

There are two main methods of code writing. One consists of using the same letters as they appear in the original message, but changing their relative positions in a definitely prearranged manner. In other words, the letters of the message are carefully scrambled. The system used in this scrambling is the secret of the code. This method of code writing is known as transposition. The other method of code writing consists of the replacement of the letters of the original message by other letters (according to a certain definite system). This method is known as substitution.