Columnar Transposition

Write the message into a grid. A keyword decides the order in which you read the columns.

Transpositiondemo

Objectives

Derive the column order from the alphabetical rank of a keyword.
Encrypt a message through the grid and read the ciphertext back.
Explain why a permutation key of m letters gives only m! orderings.

50%

Write the message across a grid, read it out down the columns in key order.

Plaintext

Columnar key (a word; its letters give the column order)

key  C O L U M N A R
     2 6 3 8 4 5 1 7
     W E H A V E A M
     O L E A B O R T
     T H E D E A L X

ciphertext: read columns in key order

ARLWO THEEV BEEOA ELHMT XAAD

The key is a permutation, not a shift. The alphabetical rank of each key letter says which column comes out next, so m letters give only m! orderings. Frequencies are untouched here too, so the attack is anagramming.

step 1/2

CPE 645 / CS 685

Columnar Transposition

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