Columnar Transposition

Write the text in rows under a keyword, then read columns in a permuted order.

Difficulty: Beginner

How it works

  1. Choose a keyword like CIPHER. Write the keyword at the top of a grid and assign column numbers by sorting the letters alphabetically.
  2. Write your plaintext row by row underneath the keyword, filling the grid from left to right and top to bottom.
  3. To encrypt, read the columns in the order of their assigned numbers, top to bottom within each column.
  4. To decrypt, recreate the same grid shape, then fill the columns with ciphertext in numeric order before reading across the rows.
  5. Columnar transposition helps you practise working with grids and illustrates how permutation alone can give secrecy.
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What is it?

Columnar Transposition is a cipher where the plaintext is written out in rows of a fixed length, and then read out column by column. The order in which the columns are read is determined by a keyword. This technique completely shatters the sequential structure of the plaintext, though it preserves the overall letter frequencies. During World War I and II, columnar transposition was often combined with other ciphers (like substitution) to create much more formidable encryption schemes.

Try it yourself

Can you decrypt this challenge?

VHVY GUVF ZRNGL (example ciphertext)

Where this shows up today

To disrupt the sequential order of letters, destroying digraph and trigraph frequencies.