This is a cipher in which every normal letter in the message is replaced with a different letter (or sometimes a symbol). For example, A becomes G, and B becomes Z, and so on. The replacements are called the cipher alphabet - ie the key - and you can think of it as a rearrangement of our normal A-Z alphabet. So the coded message consists of recognisable letters - but you're unlikely to recognise anything else at first glance! ARE YOU GOOD AT CROSSWORDS? The reason? Well, if every letter has been disguised as a different letter, then look at how often each letter appears in the enciphered message. In English E is the most common letter, so if W is the most common letter in the enciphered message then W probably means E. In Engish, T and A are the next most common letters, so you can probably match these with the next most common letters in the enciphered message. With a few letters identified, you can spot bits of words ("in", "and", "the", for example) and you will be able to fill in some missing letters. And for every letter you decipher, you'll be able to fill in others if they appear elsewhere in the message.... Click here to try out a monoalphabetic cipher Go back