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TranspositionDifficulty: Hard

Columnar transposition

Write the message in rows under a keyword and read it off by columns in the alphabetical order of the key letters.

Try it

27 characters

Result · Columnar transposition

EATB CSOL EEFC RSRU TGH SMEE

How it works

  1. 1Pick a keyword, for example ZEBRAS. Each letter of the key is one column.
  2. 2Write the message without spaces in rows under the key. The last row may stay incomplete, or you can pad it with X.
  3. 3Number the key letters alphabetically (A = 1, B = 2…). Repeated letters are numbered left to right.
  4. 4Read the columns from top to bottom in the order of these numbers. The joined text is the ciphertext.
  5. 5To decode, work out the column lengths from the ciphertext length, put the columns back in place and read row by row.

Example

Meet at the bridge

AR EEE EHG TB TI MTD

Did you know

Columnar transposition is a classic cipher used by armies in World War I. The German military used double columnar transposition (the text is rearranged twice). The famous ADFGVX cipher of 1918 also relied on it as its second step, after first replacing letters by pairs. French cryptanalyst Georges Painvin broke ADFGVX in the summer of 1918.

Try to decode

This message is encrypted with Columnar transposition using the default settings:

ART EEEN EHGO TBA TIN MTDO

Hint

The key is ZEBRAS and the last row was left incomplete (no X).

Show solution

MEET AT THE BRIDGE AT NOON

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