Here's your fourth problem set, available in both Word and PDF formats: Problem Set 4 (Word), Problem Set 4 (PDF). And here the two Excel files you'll need to tackle the ciphertext this week: Vigenere Cryptanalysis (4 Letter) and Vigenere Cryptanalysis (5 Letter). If you need a version of these files for a different keyword length, you'll need to create it yourself using these as a model. And if you need help doing that, just let me know.
Problem Set #4 is due at the beginning of class on Friday, October 3rd.