Hilariously, the program itself is its own inverse. A little bash to handle the base64 decoding, and out pops the flag.<span>python shiftcrypt.py "`echo 'CjBPewYGc2gdD3RpMRNfdDcQX3UGGmhpBxZhYhFlfQA=' | base64 -D`" | base64 -D; echo</span>