This exam is optional. If you take it and score higher on it than on a previous exam, this exam score will replace your lowest exam score.

This will be a closed-book exam. You may, however, use one new 3"-by-5" note card, the previous exams' note cards, and a calculator. Cryptanalysis aids, such as tables of characteristic frequencies, will be provided.

You should be prepared to solve problems of the following kinds.

• Answer questions about the contrast between substitution ciphers and transposition ciphers and about the contrast between "classical" ciphers and public key cryptosystems.
• Encipher/decipher/solve columnar transposition ciphers.
• Encipher/decipher simple RSA ciphers.
• Solve modular arithmetic problems, particularly those we learned to solve with the help of the (extended) Euclidean algorithm, computations related to the RSA cryptosystem, and possibly, as review topics, computations naturally arising in connection with affine ciphers and Hill's digraphic system.
• Answer questions about student project reports.

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