Delastelle's Fractional Substitution

Bifid Cipher


At first, the text is encoded using a checkerboard cipher. For example, using the key KEY we may obtain::
1 2 3 4 5
1 K E Y A B
2 C D F G H
3 I L M N O
4 P Q R S T
5 U V W X Z
The text MESSAGE is represented by
Text: M E S S A G E
Column: 3 2 4 4 4 4 2
Row: 3 1 4 4 1 2 1
The column/row coordinates are now used to obtain letters again. The numbers may be read in one of the following orders:
  1. horizontal: 32 44 ... 41 31 to obtain the result FSSLP AE
  2. upwards: 32 14 ... 22 13 to obtain the result FPSSP DI.
  3. downwards: 31 24 ... 41 23 to obtain the result YQSAG AL.
Instead of applying this procedure to the whole text, you may decide to split the text into short blocks. Finally, you may use a second, different key word for converting numbers back into letters.

Trifid Cipher


This cipher is quite similar to the Bifid cipher described above. It uses the same principle and differs only in the use of three coordinates. To imagine, think of three checkerboards holding 3 x 3 letters. A letter is is then characterized by three numbers: one for the table, one for the column and one for the row.

To proceed, you may