Encode and decode the columnar transposition cipher using a keyword. Text is written in rows under the keyword and read out by columns in alphabetical key order.
You write the plaintext in rows under the letters of a keyword, then read the message off one column at a time, taking the columns in the alphabetical order of the keyword's letters. The keyword is the key, and only the order of letters changes.
Classic transposition works on a continuous block of letters, so spaces are stripped before encoding. This is normal for the cipher and keeps the grid regular. The decoded text comes back without the original spaces.
A single columnar transposition is weak on its own, but applying it twice (double transposition) was historically considered quite strong. Here it is mainly for puzzles, learning and CTF challenges.