1. Columnar Transposition
Ref: William Stallings, Cryptography and Network Security, 3rd Edition, Prentice Hall, 2003

2. Transposition Techniques
The rail fence technique is simple--the plaintext is simply written down as diagonals and the ciphertext is produced by reading the rows.
A more complex scheme would be to write the message in rectangular form, row by row, and then to read the characters column by column.

3. Using a Key for the Columns
Now suppose the matrix is read out as a permutation of the columns.
A key could be used to indicate the order of the columns to be read.

4. Cryptanalysis of Columnar Transpositions
The transposition cipher can be recognized using frequency analysis of the characters.
The frequency analysis indicates that the cipher text frequencies match the plaintext frequencies.
The code can be broken by laying out the ciphertext in a matrix and playing around with the column positions.

5. Making the Columnar Transposition More Secure
Besides using a key, multiple transpositions could be performed.
This would be an example of “multiple stage” encryption.
The result is a more complex permutation that is not easy to determine.