C# 5.0 Programmer's Reference

Exercises ❘ 621
6. The RandomNumbers example program described in the section “Generating Random
Numbers” works but is long and cumbersome. Write a static MyRandom class that has a
GetInt method that returns a cryptographically secure random integer. Then rewrite the
example program to use the new method.
7. Rewrite the program you wrote for Exercise 6 so that it generates random doubles in the
range [0, 1). (Hint: Add a NextDouble method to the MyRandom class to generate the random
value, and make the main program use that method.)
8. Rewrite the program you wrote for Exercise 6 so that it generates integers between minimum
and maximum values entered by the user. (Hint: Use the NextDouble method you added
for Exercise 7 to add an overloaded version of GetInt that takes lower and upper bounds as
parameters.)
9. The DefaultKeyAndIV example program encrypts and decrypts a string within its button
Click event handler. That’s not a reusable approach. Rewrite the program to move the encryption
and decryption steps into separate methods. (Hints: Make the methods take the key and
IV values as parameters. Make the main program create an AesManaged object and use its
default key and IV values.)
10. Modify the program you wrote for Exercise 9 to move the encryption and decryption methods
into extension methods.
11. Write a program similar to the one shown in Figure 27-6 to encrypt and decrypt strings. What
happens if you try to decrypt a message with the wrong password What if the password is
wrong only by a single character
Figure 27-6: For Exercise 11, write a program that uses a password to
encrypt and decrypt messages.
12. Write programs to act as a sender and receiver for RSA communication. The receiver program
should have these features:
a. When it starts, the program should create an RSACryptoServiceProvider object
associated with a key stored in a key container. (If the key already exists, it will load
into the provider. If the key doesn’t yet exist, the provider will create a key and store
it in the container.)
b. After it has created the provider, the program should display the public key values
Exponent and Modulus in TextBoxes. (You can also make it display the private data
if you like.)
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