Symmetric Key Encryptions
1. Compare the following files and explain the difference by using mathematical facts.
cat_AND.bmp
cat_OR.bmp
cat_XOR.bmp
Hint: Think about the “entropy” concept and carefully analyze the truth tables of AND, OR, and XOR operations.
2. Why can’t the XOR operation in this lab be considered a one-time pad sample? What is the difference between the process in step-26 and a legitimate one-time pad operation?
3. Compare the following files. What is wrong with the second one? Why can the cat image be seen, although you used XOR operation in both?
cat_XOR.bmp
cat_XOR_2octets.bmp
4.In symmetric key encryptions, the same key is used for encryption and decryption operations. You used AND, OR, and XOR operators to “encrypt” plain-text data (bitmap file). Prove that the XOR logic operation is symmetrical, meaning that Operand B -used to encrypt the bitmap data- can be used to decrypt the encoded bitmap file. Prove this (1) mathematically (by using the truth table of the XOR operator) and (2) practicing on the Crypti tool. Send two screenshots for the proof (2) to your instructor; one showing the encryption and one showing the decryption. Note that you don’t have to use the bitmap file and hexed.it in proof (2). You can use a random string and a random operand B.
Also, show that AND and OR operators corrupt the original image because these operators are irreversible (lossy). Therefore, the AND/OR operations performed in this lab cannot be regarded as encoding, encryption, or anything similar by no means. Choose one of the operators and prove this by using the truth table (1) and practicing in Cryptii (2).
5. Upload the four image files below along with your answers.
a. cat_AND.bmp
b. cat_OR.bmp
c. cat_XOR.bmp
d. cat_XOR_2octets.bmp
6. Reflection Question: in two to three paragraphs (i.e., sentences, not bullet lists) using APA style citations if needed, summarize, and interact with the content covered in this lab. Summarize what you did as a crypto analyst, what kind of vulnerabilities did you exploit, what might have prevented these attacks. In particular, highlight what surprised, enlightened, or otherwise engaged you. You should think and write critically, not just about what was presented but also what you have learned through the session. You can ask questions for the things you’re confused about. Questions asked here will be summarized and answered anonymously in the next class.
