C&O 487 - Applied Cryptography, Assignment 1, Question 1:
Retrieve "pagexy" from the "Assignments" section on the course web site, where xy are the last two digits of your student ID number. This page contains ciphertext that was genereated using a Vigenere cipher as described in class. The secret key word is an English word (names of cities and countries are included) having no repeated letters. All punctuation and spaces were removed from the plaintext, which was then blocked off into groups of 5 letters prior to encryption. Your task is to recover the secret key word. You may use any method to find the key word, including clandestine attacks. For this problem, please only hand in the page number and the key word.
Matt's post earlier today suggests that he chose the "clandestine" approach and stole the solution from my room. Shame, Matt, shame.
Here is the source code to the program that I wrote to crack a Vigenere cipher using exhaustive key search. It will read keys from stdin, decrypt the cipher text with it, then give the candidate plaintext a score based on it's similarity to a dictionary you provide. On EOF, it outputs the the key and the plaintext with the highest score. It's mostly undocumented and I introduced a subtle flaw before posting so you'll have to find it and fix it before using it to cheat on this assignment, like Matt did (in the moral sense). Write your own damn program!
5:23:19 PM 
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