Reference no: EM132267637

Question 1. Substantiate or refute the following statement: The cryptographic basis of the Enigma machine is transposition.

Question 2. As time goes on, the size (i.e., length) of cryptographic keys tends to increase. Why is this so?

Question 3. Using the English alphabet (i.e., mod 26 arithmetic) let plaintext = {p1, p2,... , pn} and corresponding cipher text = {c1, c2,... , cn}. Suppose the encryption function is ci = pi + 10 (mod 26). You receive the cipher text message
EWEM SC K QBOKD CMRYYV. What are the decryption function and the recovered plaintext? What type of cipher is this? What are some weaknesses of this cipher?

Question 4. Briefly compare and contrast stream and block ciphers.

Question 5. Consider the following plaintext message: WATER BOILS AT 212 DEGREES FAHRENHEIT
a. If this message is sent unencrypted and successfully received, what is its entropy?
b. If this message is encrypted with 3DES (using an optimal set of keys) what is the encrypted message's entropy?
c. If this message is encrypted with AES (using the most secure key length), what is the encrypted message's entropy?

Question 6. Name some risks that cannot be mitigated with cryptographic techniques.

Question 7. An organization has 8 members. Using a symmetric cipher, it is desired that each member of the organization be able to communicate securely with any other member, without any other member being able to decrypt their messages. How many unique keys are required?

Question 8. How many bits would need to be added to DES's key in order to double its average brute-force cracking time?

Question 9. In terms of entropy, what is the goal of cryptography?

Question 10. In order to minimize bandwidth transmission requirements, does it make more sense to compress a message before or after it is encrypted?

Question 11. Which has the larger number of possible keys: a simple (monoalphabetic) substitution cipher for the 26-letter English alphabet, or DES? Why is DES considered to be the better cipher? Show the reasoning behind your answer.

Question 12. A particular cipher is implemented by combining the ASCII representation of plaintext characters with pseudorandom bytes (eight-bit binary strings of 1s and 0s) using the XOR function. In the process of encrypting a message, a character in the plaintext, a capital D, is XORed with the pseudorandom byte 10010101.
a. What is the cipher text (in binary form) generated by the encryption of the character D? (Please show your work.)
b. How is the plaintext for this encrypted D recovered? (Please show your work.)

Question 13. A hacker with access to a super computer using brute force is able to crack a 3DES message (using its most secure keying option) in 1 hour. How many hours will it take her to crack an AES message (that uses its most secure keying option)?

Question 14. Substantiate or refute the following: As the cipher text sample size becomes smaller, cryptanalysis becomes easier.

Question 15. The following cipher text is a monoalphabetic cipher:

ROXBOOG TOSOXUXUVG WGP NVTMOXXUGM, UX UE W HWTCOI XLWX W GOB XLVDMLX OCOT EXTDMMIOE UGXV OAUEXOGQO. HWEVG QVVIOZ

Decrypt this message, and briefly describe your cryptanalysis methodology. In particular, list features of the cipher text that hindered or helped your decryption process.

Question 16. Non-repudiation and authentication are terms sometimes used interchangeably. Are they different? If so, how do they differ?

Question 17. Ciphers are broadly categorized as using transposition, substitution or trap-door functions. Please provide an example of each type of cipher.

Question 18. Why wasn't John von Neumann a proponent for using pseudorandom number generators for use in stream ciphers?

Question 19. How many different possible substitutions are there for a simple Caesar cipher?

Question 20. What is a known weakness of Enigma ciphers

Question 21. A cipher that uses a one-time pad is considered unbreakable. If this is the case, why aren't one-time pads more widely used?

Question 22. Other than brute-force, what other cryptanalysis tools are commonly used to crack encrypted messages.

Question 23. What CAIN cryptographic services do each of the following provide: (1 point each)
a. Symmetric ciphers
b. Asymmetric ciphers
c. Hashing functions
d. Steganography

Question 24. The development of AES was done in a completely open manner, including detailed information regarding the algorithm used for the cipher. Was this a good idea? Why or why not?

Question 25. Fill in the blank: A ____requires that the cipher alphabet changes throughout the encryption process.
a. monoalphabetic substitution cipher
a. polyalphabetic substitution cipher
b. quantum cipher
c. alphanumeric shift cipher