INFA 640 Cryptology and Data Protection Correct Answers
Examines cryptology and data protection principles with verified answers.
James Carter
Contributor
4.8
36
about 1 month ago
Preview (4 of 11)
Sign in to access the full document!
INFA 640 Cryptology and Data Protection Correct Answers
1. A 2,000-bit message is used to generate a 256-bit hash. One the average, how many other
messages could be expected to generate the same hash value? What does this tell us about
the length of a hash as compared to the length of the message?
2. Using the English alphabet (i.e., mod 26 arithmetic) let plaintext = {p1, p2,… , pn} and
corresponding ciphertext = {c1, c2,… , cn}. Suppose the encryption function is ci = pi + 5
(mod 26). If you receive the ciphertext message RNQJDHDWZX, decrypt to recover the
plaintext. What is the decryption function, and the recovered plaintext? What type of cipher
is this? What are some weaknesses of this cipher?
3. Substantiate or refute the following statement: The cryptographic basis of the Enigma
machine is the use of a trapdoor function.
4. Consider the following plaintext message: THE BOILING POINT OF WATER IS 212 DEGREES
FAHRENHEIT. a. If this message is sent unencrypted and successfully received, what is its
entropy? b. If this message is encrypted with DES using a random 56-bit key, what is the
encrypted message’s entropy? c. If this message is encrypted with 3DES (using an optimal
set of keys) what is the encrypted message’s entropy?
5. 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 R, is
XORed with the pseudorandom byte 10010101. a. What is the ciphertext (in binary form)
generated by the encryption of the character R? (Please show your work.) b. How is the
plaintext for this encrypted R recovered? (Please show your work.)
6. The following ciphertext is a monoalphabetic ciper: 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 ciphertext that hindered or helped your
decryption process.
7. An organization has 2000 members. 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 if: a. The organization
uses a symmetric cipher. b. The organization uses an asymmetric cipher.
8. The following questions are worth 2 points each: a. Bob picked N=77 for use in a RSA-
encrypted message. Since N is part of the public key, Alice was able to crack Bob’s message
by determining the values of p and q that Bob used. What are the values of p and q did she
determined? b. Is 89,201,768 a prime number? Why or why not?
1. A 2,000-bit message is used to generate a 256-bit hash. One the average, how many other
messages could be expected to generate the same hash value? What does this tell us about
the length of a hash as compared to the length of the message?
2. Using the English alphabet (i.e., mod 26 arithmetic) let plaintext = {p1, p2,… , pn} and
corresponding ciphertext = {c1, c2,… , cn}. Suppose the encryption function is ci = pi + 5
(mod 26). If you receive the ciphertext message RNQJDHDWZX, decrypt to recover the
plaintext. What is the decryption function, and the recovered plaintext? What type of cipher
is this? What are some weaknesses of this cipher?
3. Substantiate or refute the following statement: The cryptographic basis of the Enigma
machine is the use of a trapdoor function.
4. Consider the following plaintext message: THE BOILING POINT OF WATER IS 212 DEGREES
FAHRENHEIT. a. If this message is sent unencrypted and successfully received, what is its
entropy? b. If this message is encrypted with DES using a random 56-bit key, what is the
encrypted message’s entropy? c. If this message is encrypted with 3DES (using an optimal
set of keys) what is the encrypted message’s entropy?
5. 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 R, is
XORed with the pseudorandom byte 10010101. a. What is the ciphertext (in binary form)
generated by the encryption of the character R? (Please show your work.) b. How is the
plaintext for this encrypted R recovered? (Please show your work.)
6. The following ciphertext is a monoalphabetic ciper: 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 ciphertext that hindered or helped your
decryption process.
7. An organization has 2000 members. 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 if: a. The organization
uses a symmetric cipher. b. The organization uses an asymmetric cipher.
8. The following questions are worth 2 points each: a. Bob picked N=77 for use in a RSA-
encrypted message. Since N is part of the public key, Alice was able to crack Bob’s message
by determining the values of p and q that Bob used. What are the values of p and q did she
determined? b. Is 89,201,768 a prime number? Why or why not?
Preview Mode
Sign in to access the full document!
100%
Study Now!
XY-Copilot AI
Unlimited Access
Secure Payment
Instant Access
24/7 Support
Document Chat
Document Details
University
University of Maryland
Subject
Information Technology