22C:2 From CAT Scans to Google: Great Ideas in Computing
Homework 7. Due November 2, 2006
- Do the first problem on the last page of the lecture notes for 10/26/06.
It asks you to decode a message that was encoded using the Playfair system.
Wikipedia's article on the Playfair Cipher presents the encoding/
decoding rules very clearly. Note, however, that the method used
for this problem is the "alternate" method in which characters
i and j and put in the same spot in the 5x5 table/matrix rather
than skipping q.
NOTE: To get credit for this problem, you must show at least some of the steps
in your work. Simply writing the decoded message is not sufficeint.
- Explain why no letter will ever be encoded to itself in the Playfair system.
- Read Chapter 6 of the book ("Computers Ltd: What They Really Can't Do" by Harel.)