A Caesar cipher is the earliest known tool for creating codes to encrypt messages. It is known by several other names, which include Caesar's shift, Caesar's code and the shift cipher. This code-breaker is a substitution cipher in which one letter of the alphabet is replaced by another letter that is an affixed number apart from the letter in the original message. If you want to write a message in code in this manner, the letter A would become D and all other letters would be substituted by letters that are three down in the alphabet.
The name of this method of breaking codes comes from Julius Caesar, who used this method of sending messages to his general and the old fashioned word for figuring out problems or to write in code - cipher. Caesar used the combination of three letters in all his messages. Even if the messages were found by the enemy who could speak and write the Roman language, they would likely think that this message was written in a foreign language and would not bother to try to break the code. In the typical Caesar code, A becomes D, B becomes E and so on. When you need to use the last letters of the alphabet, such as Y, you count three starting at the beginning again, so Y becomes B.
The Caesar cipher was used in Biblical times and can be found on the back of the Mezuzah where it encrypts the names of God. During the 19th century, it was quite common to see encrypted messages using this principle printed in newspapers so that they were private. During the First World War, the Russian army used this method to relay messages to troops because other modern methods of encryption proved too complicated for the troops to decipher.
To break the Caesar code, you do have to experiment with various combinations of letters until you find one that works. Every letter has the same number combination between the letters of the message and the substituted letters so once you figure out what the first word is, then it is only a simple procedure to figure out the rest of the message. There are only 26 possible combinations and by simply eliminating letters and distances between them or by looking for frequency of letters or patterns in words, one can figure out the code.
You can easily break the Caesar cipher using your computer. There is even an online site where you can enter the encrypted message and click "decipher" to find out what the message says. You can also reverse the process to encrypt a message of your choosing using this method.