You need install Decrypt 2.0 for decrypt your message (Free app on cydia).
"Crypt 2.0" is a quick encryption algorithm to allow you protect your messages,notes ect. You can send crypt messages if you chat with a person who have "Crypt 2.0".
Crypt 2.0 is a plugin action Menu.
If you let null the text field, "Crypt" will find a random key for you but you need remind your key to decrypt.
If you put a custom key , "Crypt" it will transform your key in possible key and it show you in pop up.
Never forget your key if you want decrypt your message one day, you can use the same key if you want.
Use context menu for text fields.
See larger Screenshots below..