THE ALPHABET CIPHER

 

Lewis Carroll published this cipher in 1868 in a children's magazine. It describes what is known as a Vigenère cipher, which is a well-known scheme in cryptography. Carroll claimed that if used correctly the cipher was ‘unbreakable’.

When viewing the cipher, each column of the table forms a dictionary of symbols representing the alphabet: tehrefore, in the A column, the symbol is the same as the letter represented; in the B column, A is represented by B, B by C, and so on.  To use the table, some word or sentence should be agreed on by two correspondents. This may be called the 'key-word' and should be held in memory only.

In sending a message, the key-word should be written over it, letter for letter, repeating it as often as may be necessary: the letters of the key-word will indicate which column is to be used in translating each letter of the message; the symbols for which should be written underneath, before copying out the symbols only and destroying the first paper. It purports to then be impossible for any one, ignorant of the key-word, to decipher the message, even with the help of the table.