Incomplete Columnar

Description

A more secure variation of the Complete Columnar Transposition cipher is the Incomplete Columnar Transposition cipher. As its name suggests some cells at the bottom of the block are left empty making it more difficult to determine the block width and, therefore, solve the cipher. The cipher is created by writing the plaintext into the block horizontally, leaving some of the bottom cells empty, then each column is read off vertically to form the cipher. The order in which the columns are read is determined by the alphabetic order of the letters of a keyword. The number of letters in the keyword also defines the width of the rectangle used.

Example

Key: REALITY (5214367)

Plaintext: Experience is something you don't get until just after you need it.

REALITY

5214367

EXPERIE

NCEISSO

METHING

YOUDONT

GETUNTI

LJUSTAF

TERYOUN

EEDIT

Ciphertext: PETUT URDXC EOEJE ERSIO NTOTE IHDUS YIENM YGLTE ISNNT AUEOG TIFN

Solving

Solving methods: Brute force search.

After selecting the Incomplete Columnar cipher, the cipher period can be selected from the Period drop down menu in the Cipher Settings ribbon group. The default setting of 0 will result in all periods in the keyword range set in the Options window being tested. For more in-depth searching select a specific key length.

Only those keyword lengths which produce an incomplete grid will be tested.