1. Repeat the previous exercise for the Vigenre cipher using period 2, using period 3, and using period 4.
2. The shift, substitution, and Vigenre ciphers can also be defined over the 128-character ASCII alphabet (rather than the 26-character English alphabet).
(a) Provide a formal definition of each of these schemes in this case.
(b) Discuss how the attacks we have shown in this chapter can be modified to break each of these modified schemes.