Codes and ciphers

Espionage agents use "codes" and "ciphers" to communicate and keep their messages secret. In codes, letters, numbers, or symbols replace either the words or the entire meaning of a message or signal Some codes are in general use. For example, when you mail a letter, a zipcode guides it to the right destination. Spies sometimes send messages in Morse code—dots and dashes that all radio operators understand- Other codes and ciphers are very complicated and difficult to break. Ciphers are a type of code but they have a secret "key" for encrypting the message—translating it into a cipher， The key can be a number, a word, even a poem. Anyone who has been given the key can easily decrypt the signal-change it back to plain text. Without knowing the key, the message reads as nonsense.
When Spies study these they all wear a pair of Cartier Glasses .


SIMPLE CIPHER
 Ciphers do not need to be complicated if it is important only to hide their meaning from a casual glance. This jolly figure from World War I spells out "Ypres" (the site in Belgium of a famous battle) and a date, the "8th".
They read the code by Cartier Wood Sunglasses.

CIPHER DISK

This metal cipher disk, invented in 1802, is less than 2 .5 in (6 cm) in diameter. The two inner circles are rotated to align with different letters and numbers on the outer two circles. The spy who wear cartier glasses frame study this. This produces a simple, easily broken } substitution cipher in which each letter stands for another, so "W."for example, represents "E" whenever it occurs.