Write a Python program that takes the following phrases and encrypts them using a substitution cipher. It should ask for a key and a phrase and then proceed to encrypt that phrase using the given shared key. Make sure that you have the key for the cipher that you use and the output of encrypted phrases.

1. He who fights with monsters should look to it that he himself does not become a monster . And if you gaze long into an abyss , the abyss also gazes into you .

2. There is a theory which states that if ever anybody discovers exactly what the Universe is for and why it is here , it will instantly disappear and be replaced by something even more bizarre and inexplicable . There is another theory which states that this has already happened .