Trifid Cipher (History and Example)

Trifid cipher is a trigraphic substitution cipher where each letter of the plaintext depends on three letters of the plaintext and up to three letters of the key.

It is also known as the 3 digit number cipher.

It combines substitution with transposition and fractionation.

Trifid cipher uses a table to fractionate each plaintext letter into trigram, mixes the constituents of the trigrams, and then applies the table in reverse to turn these mixed trigrams into ciphertext letters.

Differences between trifid cipher and bifid cipher:

  • In trifid each symbol is divided into three while in bifid each symbol is divided into two.
  • Bifid cipher uses the polybius square to turn each symbol into coordinates on a 5 by 5 square while trifid turns each symbol into coordinated on a 3 by 3 by 3 cube.
  • In trifid cipher, a particular output symbol is dependent on three inputs while bifid is dependent on two inputs.
  • Trifid cipher has a greater degree of diffusion compared to bifid cipher.

A brief history of trifid cipher:

It was invented by Felix delastella in 1901.

Delastelle also invented the bifid cipher and four-square cipher.

Are you interested in finding out more about ciphers and codes?

The Codebreakers – The Story of Secret Writing book by David Kahn is what I would start with.

Trifid Cipher

In this guide I will be discussing the following:

  • How to solve the trifid cipher.

1) How to solve the trifid cipher

How to encrypt using trifid cipher:

First step is to use the cube to convert the letters into numbers.

Then write the numbers vertically below the message in the order of Layer, column, and Row.

trifid cipher

Here is an example:

Plaintext: Kifanga.




Then I read off the numbers horizontally and group them into triplets.

211 121 123 312 111 321 231

Finally I use the cube again to convert the numbers back into letters.

Thus, ciphertext: jbhvatl.

How to decrypt trifid cipher:

First you need to convert each letter into its corresponding number using the cube. Then divide the long string of numbers into three equal rows.

Finally read off each column and use the cube to convert the three numbers into the plaintext letter.

Are you interested in learning how to break codes?

The Elementary Cryptanalysis – A Mathematical Approach book by Abraham Sinkov is what I would recommend.

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