Code Breaking and Decoding Tools

The following codes and ciphers are detailed below, click to go straight to one or carry on reading:
Modern CodesAtbash CipherCaesar ShiftCaesar SquareAnagramsSubstitution CiphersOther Ciphers.

Creating and decoding secret messages has played a pivotal role throughout history and in many fictional novels, from the Caesar Cipher by Julias Caesar, through to the Enigma Machine in World War II to the various codes in Dan Brown's novel The Da Vinci Code.

Detailed below are various decoding tools, starting with the simplest and progressing to the increasingly complicated. In The Da Vinci Game, several of the Logic Key challenges use simple variants of these codes which can be deciphered manually. They are provided here simply for your enjoyment.

For more information about The Da Vinci Board Game itself, please see the links on the left.

Modern Codes

The invention of the computer along with the development of modern Internet connection media like broadband, has meant that modern codes are immeasurably more complicated than the codes described below, with the possibility to transform a message in innumerable ways. The Enigma machine used in World War II is probably the earliest example of this.

Even with this encryption the challenge is still to pass on the decoding mechanism or key to the intended recipient of messages in a way in which it cannot be intercepted, as if the key falls into someone else's hands, then you may as well be writing your code in plain English.

Atbash Cipher

The Atbash Cipher is a simple substition cipher where the first letter of the alphabet is exchanged with the last letter of the alphabet and so on. It is the simplest cipher because it only allows one possible way to decode a word. That said, the cipher will vary depending on the alphabet; for the English alphabet simply exchange the letter in the code for the letter either below or above it in the following table:

Atbash Cipher, used in The Bible and The Da Vinci Code

Q1. Using the Atbash cipher, what does the code YRYOV become? (a book that contains several words coded using this cipher).

Caesar Shift Decoder (also called the Caesar Cipher)

The Caesar Shift allows you to encode text in one of 25 different ways, by shifting each letter between 1 and 25 'steps' along the alphabet, so a shift of 1 would mean A becomes B, B becomes C, etc. To download a free copy of a Caesar Shift Decoder which allows you to see all 25 possible Caesar Shifts simultaneously, please click here. You will need Microsoft Excel to view and use the attachment.

The Caesar Shift or Caesar Cipher can be made more complicated by having a different shift for different letters in the sequence, as in the recent code that Judge Peter Smith hid in the document of this judgement in The Da Vinci Code vs. Holy Blood, Holy Grail case.

Q2. Using the Caesar Cipher, what does the code P BOO WK CYX become? (indicating an affiliation with a certain secret society). 

Caesar Square or Box

The Caesar Square requires the decoder to omit any spaces and then rewrite the code in a square and read down the columns to reveal the answer, so for example to encode the phrase 'What an unusual box', first omit the spaces to get 'WHATANUNUSUALBOX' and then write them in a box as follows:

The Caesar Square or Caesar Box

To write this in code, you would then print 'WA ULH NS BA UU OT NAX' (the spaces are unimportant).

While it would be possible to use a rectangle instead of a square, a square is the standard mechanism for this particular encoding device, therefore if the number of letters in a code is a square number (9, 16, 25, 36, etc.) it may indicate a Caesar Square is being used.

Q3. Using the Caesar Square, what phrase is revealed here: 'CAE EG ELLNE NIL CNT NI ECRT GAY' (an organisation who spend plenty of time cracking codes themselves).


Anagrams are where the order of letters is rearranged to form a new word or phrase, so EARTH can become HEART and SECURE can become RESCUE.

The longer the anagram the more difficult a code is to solve, some codes can be set where a standard algorithm to change the place of letters is used (e.g. the first and seventh letters are swapped, the second and forth letters are swapped, etc.) To create the Vitruvian Man clues in The Da Vinci Game, we used Anagram Genius (TM) which orders anagrams into the most likely and most interesting first and was also used by Dan Brown to generate the Anagrams used in The Da Vinci Code.

Q4. What city is 'GNASH ON WIT' an anagram of?

Other Substitution Ciphers

A more complex substitution cipher is where letters are replaced with other letters at random, so A might become Y, B could become D, etc. It's practically impossible to crack short codes written using this, unless you discover the key, however for longer codes frequency analysis can be used, whereby you count how many times each letter appears in the code and compare this to the frequency of how commonly different letters normally appear in the alphabet.

For example, if the letter 'Q' appears the most often in a code, it will probably be a common letter, such as 'E', 'T' or 'A'. The following graph shows how frequently different letters crop up in the English language, courtesy of Wikipedia:

Frequency Analysis Decoding Tool

A clever coded message will hide the frequency by carefully using, for example few words that include the letter E in the message to be decoded. Some codes also use punctuation, numbers and even spaces as part of the code and also deliberate mis-spellings to make it more difficult for the solver.

Q5. Can you decode the quote from the play Julius Caesar by William Shakespeare:

"Juemrn rby heiw obhyn nypjmy oaybm ryeoan; ay segbeio iysym oenoy jp ryeoa nqo jicy.
P egg oay ujirymn oaeo wyo aesy ayemr, bo nyyhn oj hy hjno nomeity oaeo hyi najqgr pyem;
yybit oaeo ryeoa, e iycynnemw yir, ubgg cjhy uayi bo ubgg cjhy."

Other ciphers

In addition to the ciphers above there are many other ways to code messages and the most difficult codes will use a range of different encryption methods, such as applying a sustitution cipher and then rearranging the letters using a Caesar Square or some other method.

Another way to hide codes is to hide them in plain sight, where for example the fifth letter in every paragraph makes a code, or a grid is placed over text with small holes in it and only the letters you can see through the holes are read. This means that a passage of text is unlikely to be recognised as a code so an attempt to decode it is less likely.

Modern CodesAtbash CipherCaesar ShiftCaesar SquareAnagramsSubstitution CiphersOther Ciphers.