Generic Transposition Cipher

Description

The text to be processed is filled into a table, the cipher text is obtained by reading the letters in a different way. For example, you might fill the table line by line and read the cryptogram column by column.

For longer messages, its more convenient - for paper and pencil application - to split the message into smaller blocks. So you may choose a square block, a user defined block, or use a single block. CipherClerk's Applet only requires to enter the number of lines of a block if you want to choose a user defined block. In the other cases, the block size is derived from the key word: If not mentioned, the number of rows matches the number of letters in the key word.

By default CipherClerk's Applet will fill the table completely, appending a pad string to the plain text. By checking use irregular transposition, you may suppress this. In such a case the empty fields of the table are determined by writing the text left to right and line by line into the table. If there remain some empty fields, they are marked. When the plain or cipher text is filled into the table, these fields will remain empty.

CipherClerk's Applet offers several choices how to fill in the table and to take of the result. Obviously, for deciphering one must fill the table in the order it was read when it was enciphered. Note that you must always set up CipherClerk's Applet as if you would encipher the message. CipherClerk's Applet takes care to use you setup correctly when deciphering.

The choices available for fill in / take of are:

by columns

The text is read/written column by column. You may specify where you want to start: top-left, top-right, bottom-left, or bottom-right. You may permutate the columns using a permutation based on the key word. Finally, you may choose to trace columns in alternating directions.

by lines

The text is read/written column by column. The options are the same as before.

by diagonals

The text is read/written along diagonals. You may choose where to start, whether the diagonals should be traced upwards or downwards, and whether this tracing direction should be alternated or not. A square block is required.

spirally

The text is read/written along a spiral line. You may choose where to start, whether the spiral is clockwise or not. If expanding is checked, reading/writing starts at the center and processed to the specified corner. While a square block is required, an even block size is not.

nihilist

The text is read column by column and line by line where both - columns and lines - are permutated. If lines first is checked, the text is read line by line and column by column, both permutated. A square block is required.

rot. grille

A square grille is prepared: The key is truncated to a length of n^2, e.g. to 4, 9, 16, 25, or 36 characters. The size of the grille is chosen 2n and n^2 openings are cut into the 4 n^2 fields of the grid. The grille is laid on the table and the text is read/written through the holes left to right, line by line. Then the grille is rotated by 90° clockwise (or counter-clockwise) and text is continued to by read/written.

Ofcourse the holes are set up in a way that each field of the table is exactly visible once: The table is divided into 4 squares filed, each of the size n x n. The fields in the top left square are numbered (left to right, top to bottom) 1 to n^2. The fields in the other squares are numbered so that when rotating the grill the numbers in a field remain unchanged. For example, if the key length is 9, we obtain:

1 2 3 7 4 1
4 5 6 8 5 2
7 8 9 9 6 3
3 6 9 9 8 7
2 5 8 6 5 4
1 4 7 3 2 1
Now the key word is converted into a numerical key the normal way. For example, the key DAVID KAHN yields 3-1-9-6-4-7-2-5-8. The first/second/third/forth quarter of these numbers, 3-1 / 9-6 / 4-7 / 2-5-8, denotes the position of the holes in the first sub-square. Thus the resulting grille, with holes denoted by underscores, is
_ X _ X X
X X X X X X
X X X _ _ X
X X X X _ X
X X X X _ X
X _ _ X _ X


To proceed, you may