The poem code is a simple, and insecure, cryptographic method. The method works by the sender and receiver pre-arranging a poem to use. The sender chooses a set number of words at random from the poem and gives each letter in the chosen words a number. The numbers are then used as a key for some cipher to conceal the plaintext of the message. The cipher used was often double transposition. To indicate to the receiver which words had been chosen an indicator group is sent at the start of the message.