Cryptography is the science of writing messages in code. These codes can involve letters, numbers or symbols, but the purpose of all the coded messages is the same: to communicate something to specific readers while preventing others from understanding it. Complex codes, sometimes called ciphers, are used today by governments as well as corporations trying to protect their most valuable secrets. The message can only be unveiled by the receiving individual who holds the key, or the solution to cracking the code and deciphering the message. If you should find yourself in possession of a coded message, there are numerous well-known keys in existence that may help you to find out the hidden communication.

Ottendorf Cipher

In an Ottendorf cipher, information hidden within certain books is translated into a numerical system to pass on information. For this, begin by separate the series of numbers in the code you've found into groups of three. For example, if you have been given the numbers 1, 2, 3, 4, 5, 6, you will separate them into 2 groups: 1, 2, 3 and 4, 5, 6. Keep the numbers in their original order.

Determine the book or paper to which the cipher is referring. In an Ottendorf cipher, each set of three numbers stands for a letter. The first number refers to a page in a particular book. The second number refers to a line on that page, and the third number refers to the letter in that line. In order to crack the code, you must determine what book to use. In order to determine that book or document, there must be another clue provided to you by the person who wrote the coded message that will point you to it. This could be a riddle or message in non-coded language that was passed on to you with the code, or it could simply be the code writer's favorite book. For example, if the person who sent the code included it with the riddle, "Thomas Paine will help you," it would be wise to look first at Thomas Paine's most famous book, "Common Sense," to solve your coded message.

Look up the page number, line number and letter number for each set of values you have been given. Write down the letters. Do this in the order the numbers have been provided to you. When you have found all the letters, they will form a word or sentence which is your encrypted message.

For example, if we were using the paragraph above to be considered our "book," and the code for the first letter was "1-1-4", we would look on the first page, first line and fourth letter, which here is "K."

Substitution Cipher

Substitution ciphers require replacing each of the letters or numbers given to you with a different letter. In these, there will be key which would show you what the letters, numbers or symbols provided to you actually represent. If you have this key, it is easy to go symbol by symbol and substitute in the right letter. Without the key, you will have to try doing it by trial and error.

Focus on one and two letter words such as "I", "an", "is" or "or." Substitution ciphers often put spaces in between symbol groupings to denote words. One or two letters together will make a short word, and there are not many short words in the English language for you to try. If you have determined definitely that a symbol represents a letter, replace that symbol with the letter you believe it to mean in all instances where it appears in the code. For example, if you believe "$" means "Q", replace all "$" signs with "Q".

Keep track of your key by writing the alphabet down on a separate piece of paper and writing each symbol which represents it above the letters. If you are incorrect about the key the first time, these incorrect keys will help remind you of solutions you have already tried when you redo the problem.