![]() ![]() Finally, they ought to be concatenated to form one ciphertext message. Then, the letters should be read row by row, starting from the top one. Next, the plaintext letters will form the shape of the fence: T Let's assume that the secret key is 3, so three levels of rails will be produced.įirst, we will remove the empty spaces, and encrypt only the capitalized letters: This number cannot be very big, so the number of possible keys is quite limited.įor example, let us encrypt a name of one of the countries in Europe: The United Kingdom. It is also a number of rows of letters that are created during encryption. The secret key is the number of levels in the rail. ![]() The letters should be read in rows, usually from the top row down to the bottom one. Next, all the letters should be read off and concatenated, to produce one line of ciphertext. The shape that is formed by the letters is similar to the shape of the top edge of the rail fence. To encrypt the message, the letters should be written in a zigzag pattern, going downwards and upwards between the levels of the top and bottom imaginary rails. The letters are arranged in a way which is similar to the shape of the top edge of the rail fence. Currently, it is usually used with a piece of paper. It was used by the Greeks, who created a special tool, called scytale, to make message encryption and decryption easier. The Rail Fence Cipher was invented in ancient times. This simplistic method of cryptanalysis (checking every single possible key) only works on very simple ciphers such as this cipher, even slightly more complex ciphers can have far too many keys to check all of them.The Rail Fence Cipher is a transposition cipher, which rearranges the plaintext letters by drawing them in a way that they form a shape of the rails of an imaginary fence. So the method used is to take the ciphertext, try decrypting it with each key, then see which decryption looks the best. Of course, the more ciphertext you have, the more likely this is to be true (this is the case for all statistical measures, including the frequency approaches above). The key that results in a decryption with the highest likelyhood of being english text is most probably the correct key. For automated methods of determining how 'english like' a piece of text is, check out the Classical Cryptanalysis section, in particular Quadgrams as a fitness measure. In other words it should look just like this: English Letter Frequenciesįor a method that works well on computers, we need a way of figuring out which of the keys results in the most english like plaintext after decryption. ![]() Anagramming is another very powerful method that can be used with any transposition cipher, that consists of taking chunks of ciphertext and guessing what the plaintext would be.Ī peculiarity of transposition ciphers is that the frequency distribution of the characters will be identical to that of natural text (since no substitutions have been performed, it is just the order that has been mixed up). It is very easy to find a key if you know some of the plaintext, or can guess some of it. A cryptanalyst (code breaker) simply has to try several keys until the correct one is found. The railfence cipher is a very easy cipher to break. This is a JavaScript implementation of the Railfence Cipher.Ĭryptanalysis is the art of breaking codes and ciphers. The ciphertext is again read off along the rows: dttfsedhswotatfneaalhcleelee JavaScript Example § The ciphertext is read off along the rows: dnetlhseedheswloteateftaafcl We write it out in a special way on a number of rails (the key here is 3)ĭ. The key for the railfence cipher is just the number of rails. This is equivalent to using an un-keyed columnar transposition cipher. ![]() Many websites claim that the rail-fence cipher is a simpler "write down the columns, read along the rows" cipher. The railfence cipher offers essentially no communication security, and it will be shown that it can be easily broken even by hand.Īlthough weak on its own, it can be combined with other ciphers, such as a substitutionĬipher, the combination of which is more difficult to break than either cipher on it's own. It is a transposition cipher that follows a simple rule for mixing up the characters in the plaintext to form the ciphertext. RAIL FENCE CIPHER PROGRAM CODE CRACKThe railfence cipher is a very simple, easy to crack cipher. ![]()
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