This app allows you to encrypt a text message using the Gronsfeld cipher. Simply enter a message and a numeric key, press apply and generate your encrypted message.

Tap on the message to copy it to your clipboard and paste it in any email, text or tweet. Only people who know your key (and have this app!) can recover the original message.

The app includes a Share menu button that will send the download page for this app to another person - perfect for quickly setting up your own spy ring.