the encrypt code is "ARJHNRIUCGQHPFGQFHTXPDEHTLNOC", and the part that i know of the plaintext is "DERUNA".
The key is period of 2, so the key are 2 letters. Each letter of the code would specify in turn the magnitude of the cyclical shift.
How i can find the key? And how I can break the cipher?
I have to create a program in c++ that automatically decrypt the message.