Problems

Use the following problems to test your skills at building cryptographic programs. Give each problem a try before you turn to the example solutions for help.

45. Caesar cipher

In a Caesar cipher, also called a Caesar shift, Caesar substitution cipher, or shift cipher, you shift the values of the letters in the message by some fixed amount. In the original Caesar cipher, Julius Caesar reportedly used a shift of three to send secret messages to his commanders, so each letter was replaced by the letter that comes three positions later in the alphabet. The letter A was encrypted as D, B was encrypted as E, and so forth. Letters at the end of the alphabet wrap around to the beginning so, for example, X becomes A, Y becomes B, and Z becomes C. In this example, the shift value, 3, was the cipher's key.

Write a program that uses a Caesar cipher to encrypt and decrypt messages. Let the user enter some text and a shift and then click a button to encrypt the message. Let the user then enter a...