This problem uses a real-world example, from an old U.S. Special Forces manual (public domain). A copy is available at this book's Web site.

a. Using the two keys (memory words) cryptographic and network security, encrypt the following message:

Be at the third pillar from the left outside the lyceum theatre tonight at seven.

If you are distrustful bring two friends.

Make reasonable assumptions about how to treat redundant letters and excess letters in the memory words and how to treat spaces and punctuation. Indicate what your assumptions are. Note: The message is from the Sherlock Holmes novel, The Sign of Four.

b. Decrypt the ciphertext. Show your work.

c. Comment on when it would be appropriate to use this technique and what its advantages are.