Columnar

Explanation

The Columnar cipher, also known as the Columnar Transposition cipher, is a type of transposition cipher where the characters of the plaintext are rearranged according to a specific method based on the columns of a grid.

Start by writing the plaintext message into a grid, row by row, with a fixed number of columns. The number of columns is determined by the key, which is a word or a sequence of letters chosen by the sender.

Arrange the columns of the grid in alphabetical order based on the letters of the key. For example, if the key is 'KEYWORD', arrange the columns of the grid in the order of the letters in 'KEYWORD'.

Read the ciphertext from the grid by going column by column, starting with the column that corresponds to the first letter of the key, then the second letter of the key, and so on, until all columns have been read.

The Columnar cipher is relatively simple to implement and understand, and it provides a moderate level of security against casual attempts to decrypt it. However, it is vulnerable to more sophisticated cryptanalysis methods, especially if the key is short or if there are patterns in the plaintext.

Facts

It was used by many military forces and intelligence agencies in World War I and II