Question

Hands-On Project 9-1

In this project, you perform bit-shifting on a file and verify that the file can be restored.

1. Start Notepad and type the following in a new text document: This document contains very sensitive information. We do not want the competition to be able to read it if they intercept the message.

2. Save the file as correspondence.txt in your work folder, and then exit Notepad.

3. Start WinHex, and open the correspondence.txt file.

4. Click Edit, Modify Data from the menu. In the Modify Block Data dialog box, click the Circular left rotation option button, and then click OK.

5. Save the file as correspondence1.txt, and exit WinHex.

6. Restart WinHex, and open correspondence1.txt. Click Edit, Select

   All from the menu.

7. With the file’s contents highlighted, click Edit, Modify Data from the menu. In the Modify Block Data dialog box, click the Circular left rotation option button, if necessary, to rotate the bits, and then click OK. Repeat this step seven times to verify that you can recover the data.

8. When you have recovered the text to its readable state, save it as correspondence2.txt.

10. Write a short paper stating whether you think this method is a reliable one for encrypting. Leave WinHex running for the next project.

Answer 1

Encryption is the process of encoding a message or information in such a way that it can only be read by an authorized party.

Bit-shifting encryption is the method of shifting a 'w' bits word through 'r' bits, it helps increase the number of permutations required to decode a message. Although, bit-shifting algorithms are often used in combination with other bitwise operations such as Bitwise AND, OR, NAND, NOR, etc.

In Shannon's landmark paper Communication Theory of Secrecy Systems, published in 1949, he discussed two traits of secure ciphers: confusion and diffusion. Confusion states that the relationship between the symmetric key and cipher text should be complex, whereas diffusion focuses on the relationship between plaintext and ciphertext.

The above mentioned method allows for good diffusion because of the presence of circular rotation. Most of our modern-day encryption methods are based on the concept of rounds because they carry the bits of plaintext to new locations. Once these bits are in these new locations, we often perform other mathematical of bitwise operations on the text to increase diffusion. Whereas, in the above example, we are not employing any such operation after performing circular bit-shift and thus the above mentioned example offers us only moderate level of reliability.

A well equipped hacker could get into our text and recover the encrypted information with not much difficulty, whereas a naive of regular user would not be able to.