Columnar Transposition

What is Columnar Transposition?

Columnar transposition is a cipher that rearranges plaintext by writing it in rows under a keyword, then reading it out column by column in an order determined by alphabetically sorting the keyword letters.

How It Works

Encryption

1. Write the keyword across the top
2. Number the columns based on alphabetical order of the keyword
3. Write the plaintext in rows beneath the keyword
4. Read the columns in numerical order

Example

Keyword: SECRET, Plaintext: HELLOWORLD

S E C R E T  →  Column order: 4 1 0 3 2 5
H E L L O W
O R L D X X

Reading columns 0,1,2,3,4,5: LLEROOXWLDHX

Decryption

1. Calculate the number of rows needed
2. Fill in columns in the keyword's alphabetical order
3. Read off rows to get plaintext

Columnar Transposition in Geocaching

This cipher appears in geocaching puzzles because:

• Keyword-based: Finding the keyword is part of the puzzle
• Visual: The grid can be displayed as a clue
• Historical: Used in World War I and II
• Moderate difficulty: Harder than simple ciphers but solvable

Breaking the Cipher

Without the keyword:

• Guess keyword length: Try different column counts
• Anagram columns: Rearrange until text appears
• Common patterns: Look for TH, HE, AN combinations
• Cribs: Use known words to determine order

Variations

• Double columnar: Encrypt twice with different keywords
• Irregular columnar: Use partial last row
• Myszkowski: Handle duplicate letters differently

History

Columnar transposition was widely used during World War I and II. The German ADFGVX cipher combined columnar transposition with substitution. The cipher was considered quite secure for its time when double encryption was used.