BZCES'A FM ASMV RB ZQYFG O VAEUH TAEUH
WF Y YWOZR AWOZR YWSW RBBQYFG
TWJ Y AWOZR YWOZR'F PCL Y FZQYFG ZQYFG
CV S JVUPL LVUPL JVYM LMAWOZR

Massive Hint

Most simple ciphers (codes) use a key to encrypt messages. At it simplest, a key is just a number. For example, Caesar is said to have encoded his messages by replacing each letter with the letter that occurs three places later in the alphabet. That is, he replaced A with D, B with E, C with F, and so on. The current Latin alphabet is slightly different to the one he used, but in modern terms we would convert plain text into cipher text by making the following substitutions.

In this case, because each letter is "displaced" by three characters, we say that the key is the letter "C" (because C is the third letter of the alphabet). Once you know the key, deciphering a message is trivial, and even if you don't know the key, it's often very easy to work out what it must be, especially if you know which letters occur most frequently in the plain text. For example, if the plain text is a randomly chosen phrase written in standard English, the three most frequently occurring characters in the cipher text may well correspond to E, S, and T.

To overcome this problem, the Vigenère Cipher uses a word as its key. The first letter of the message is encoded using the first letter of the key, the second letter of the message using the second letter of the key, and so on. If you run out of letters in the key, you simply cycle back to the beginning and start again. Thus, if the key were the word NOISY, the message would be encoded using each of the following rows in turn, returning to the first row as often as necessary:

Note. When trying to crack a message written in Vigenère Cipher, the best way to start is to deduce the length of the key word. Suppose, for example, that a message contained lots of copies of the letter-pattern "AND", and these just happen to occur in groups 14, and 35 and 49 characters apart from each other. If the key just happens to be 7 letters long, there's a good chance that you'll end up encoding the letters "AND" with exactly the same rows of cipher-text on several occasions, and this will show up in the encoded message as a repeating block of the same 3 cipher-text letters. These occurrences must, of course, be some exact multiple of 7 letters apart, because the key has to line up exactly the same in each case. In general, to find the length of the key look for repeating blocks of letters in the encoded message, and then count the numbers of letters between them. Find a number that divides all of these gap lengths evenly, and that's a good candidate for the length of the key. Once you know how long the key is, you can split the message into a number of chunks and perform normal letter-counting to try finding E, S, T and so on.