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According to the "legend", Polybius square cipher would have been used by russian nihilists jailed into the Tsar cells toĬommunicate. Moreover, this cipher allow people to communicate by knocking on any surface (like morse code). The numeric codes composing this cipher was so translated using torches, which wasn't easy because you needed ten torches to transmit This substitution cipher was first created to improve "long distance" transmission techniques. Then the rest of the grid will be filled with the other letters that wasn't used into the key, in alphabetical order. This key will be placed at the beginning of the grid, It's also possible to add a secret key when you encrypt the data, so it will improve the cipher security (even though it's now very unreliable to encrypt data with such a cipher). "B" will be replaced by "12" because it is on the first line but second column, and so on. "A" will so be represented by "11" in the cipher. For instance, the "A" letter will be the first in the grid, into theįirst line and first column. Then, we just have to replace the input's letters by the two numbers in the grid that represent its coordinates. We fill the grid startingĪt the top left corner, ending at the bottom right. In english it's the "J" or "I" that is being excluded. For instance in french we take out the "W" letter. This letterĪctually depends on which language is used to encrypt or decrypt the input. As you see, there's only 25 boxes in the grid, which mean that we will need to exclude one letter. There's also a 36 boxes variant which allow the user to encrypt numbers too. The principle isįirst, we fill a 25's boxes grid (5 by 5). Polybius square took its name from its creator, Polybius (greek historian who lived around 200 to 125 BC). The encryption process - unlike the polyalphabetical ciphers (such as Vigenere cipher for instance). This kind of ciphers are named like that because they proceed by substitute the input letters by always the same values during all Polybius Square is a substitution cipher, also known as monoalphabetical cipher.