This week I want to introduce a topic that’s of interest to me, and that is the columnar transposition ... which is where this cipher gets its name. To get the encoded message, copy down the ...

We return to the series on columnar transposition ciphers to discuss permutations, how CTCs can be thought of as permutations, and some questions that this connection opens up.

To decrypt a double transposition, construct a block with the right number of rows under the keyword, blocking off the short columns. Write the cipher in by columns, and read it out by rows.