The Caesar cypher is a code with the simple principle that the alphabet is shifted along a certain number of times, for example, if it was shifted 12 times, then the letter that would replace A would shift 12 along and become M. Every letter would be substituted by the letter 12 letters after it in the alphabet. To decrypt this cypher, one of the easiest methods is to complete a tally of all the letters of the alphabet and how many times they appear in the encrypted text. The letter which appears the most frequently, is likely to be the letter E as it is the most common letter in the English language, however it is not certain so it is a good idea to check it fits before you start substituting it in. To do this you can look at words which appear often for example “the�. If you see the same three letter word appearing on multiple occasions with the letter you think substitutes E as the last letter, then this means that it is even more likely to be correct. From here we just need to copy out the decrypted alphabet alongside the plain text alphabet. In the diagram to the right, the blue letters represent the encrypted alphabet and the red the decrypted. As you can see, in this example E is substituted with F which means that the alphabet has been shifted along once. This means that we can now fill in what all the other letters are substituted with. Each letter will be replaced with the one that follows it. So if the code was: UIJT JT IPX UP TPMWF B DBFTBS DZQIFS Then you would now know that it would mean: THIS IS HOW TO SOLVE A CAESAR CYPHER
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