1. What is the purpose of S-Boxes in DES algorithm? a. Substitution and Permutation b. Nonlinear permutation and complexity c. Nonlinear substitution and choice d. Substitution and expansion 2. Which of the following statements is false? a. A stream cipher is one that encrypts a digital data stream one bit or one byte at a time. b. A block cipher is one in which a block of plaintext is treated as a whole and used to produce a ciphertext block of equal length. c. Asymmetric ciphers use one key and symmetric ciphers use two keys. d. None items. 3. Which of the following statements is true? a. Cryptanalysis attack exploits the characteristics of the algorithm to attempt to deduce a specific plaintext or to deduce the key being used. b. Brute-force attacks try every possible key on a piece of cipher text until an intelligible translation into plaintext is obtained. c. In brute-force attacks on average, half of all possible keys must be tried to achieve success. d. All items.

1. What is the purpose of S-Boxes in DES algorithm? a. Substitution and Permutation b. Nonlinear permutation and complexity c. Nonlinear substitution and choice d. Substitution and expansion 2. Which of the following statements is false? a. A stream cipher is one that encrypts a digital data stream one bit or one byte at a time. b. A block cipher is one in which a block of plaintext is treated as a whole and used to produce a ciphertext block of equal length. c. Asymmetric ciphers use one key and symmetric ciphers use two keys. d. None items. 3. Which of the following statements is true? a. Cryptanalysis attack exploits the characteristics of the algorithm to attempt to deduce a specific plaintext or to deduce the key being used. b. Brute-force attacks try every possible key on a piece of cipher text until an intelligible translation into plaintext is obtained. c. In brute-force attacks on average, half of all possible keys must be tried to achieve success. d. All items.

Computer Networking: A Top-Down Approach (7th Edition)

7th Edition

ISBN:9780133594140

Author:James Kurose, Keith Ross

Publisher:James Kurose, Keith Ross

Chapter1: Computer Networks And The Internet

Section: Chapter Questions

Problem R1RQ: What is the difference between a host and an end system? List several different types of end...

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Question

10. Which of the following statements is false about the mode of operation in block cipher?
a. A mode of operation is a technique for enhancing the effect of a cryptographic algorithm.
b. One of the most limitation of ECB mode is exploitation of repeating patterns in message.
c. One of the most limitation of OFB mode is propagation of errors in several blocks after the error.
d. None items.
11. Which of the following statements is false about the CTR mode of operation?
a. is suitable for high-speed network encryptions
b. can do parallel encryptions
c. can preprocess in advance of need
d. is difficult
12. Which of the following statements is false about the public key cryptography?
a. developed to address key distribution associated with symmetric encryption.
b. developed to address to address digital signatures.
c. feasible to determine private key from public key.
d. who encrypt a message cannot decrypt the same message.
13. What is the encryption value for the following parameters using the RSA algorithm?
p=3; q=11; e-7, M=5
a. C=26
b. C=14
c. C=57
d. C= 19
14. Which of the following statements is false about the message authentication?
a. public key encryption can provide a measure of authentication.
b. symmetric encryption cannot provide a measure of authentication
c. MAC uses of a secret key to generate a small fixed-size block of data that is appended to the message
d. none items
15. Which of the following statements is false about the message authentication?
a. MAC can be used as digital signature.
b. MAC is a many-to-one function
c. MACs should be uniformly distributed
d. MAC should depend equally on all bits of the message
16. Which security services are shown in the following figure (S is a shared secret value)?
M
a. non-repudiation, availability, access control
b. digital signature, data integrity, availability
c. confidentiality, data integrity, authentication
d. access control, digital signature, confidentiality
K
c. use of centralized key distribution
d. none item
17. Which of the following statements is false about the key distribution center (KDC)?
a. hierarchies of KDC's required for large networks.
b. session key lifetimes should be limited for greater security
E(K, [M || H(M || S)])
c. public-key authority
d. public-key certificates
18. Which of the following techniques is the best for distribution of public keys?
a. public announcement
b. publicly available directory

1.
2.
What is the purpose of S-Boxes in DES algorithm?
a. Substitution and Permutation
b. Nonlinear permutation and complexity
c. Nonlinear substitution and choice
d. Substitution and expansion
Which of the following statements is false?
a. A stream cipher is one that encrypts a digital data stream one bit or one byte at a time.
b. A block cipher is one in which a block of plaintext is treated as a whole and used to produce a
ciphertext block of equal length.
c. Asymmetric ciphers use one key and symmetric ciphers use two keys.
d. None items.
3. Which of the following statements is true?
a. Cryptanalysis attack exploits the characteristics of the algorithm to attempt to deduce a specific
plaintext or to deduce the key being used.
b. Brute-force attacks try every possible key on a piece of cipher text until an intelligible translation into
plaintext is obtained.
c. In brute-force attacks on average, half of all possible keys must be tried to achieve success.
d. All items.
4. Which of the following statements is true?
a. In symmetric ciphers, as the key length increases, the system security increases.
b. DES encrypts data in 64-bit blocks using a 56-bit key.
c. In symmetric ciphers, both sender and receiver are equivalent.
d. All items.
5. Which of the following statements is true?
a. In cryptography, encryption/decryption algorithms are clear for both sender and receiver.
b. One of the most important issue in symmetric cypher is the secure distribution of the key between the
sender and receiver.
c. There are 16 rounds of processing in DES algorithm.
d. all items
6. Which of the following statements is true?
a. All items.
b. The process of decryption with DES is essentially the same as the encryption process.
c. In DES algorithm, from the original key 16 subkeys are generated.
d. In DES algorithm, there are 8 S-Box which each of them convert 6 bits to 4 bits.
7. Which of the following statements is true?
a. The number of bit shifts varies in different rounds of key scheduler in DES algorithm.
b. Triple DES uses 3 or 2 different keys.
c. AES is a block cipher method which limits the block length to 128 bits.
d. All items.
8. Which of the following statements about the AES is true?
a. Input plaintext is stored in a state matrix.
b. Key is expanded to array of 32 bit words.
c. Each rounds (except final round) consist of four distinct transformations.
d. All items
9. Which of the following statements about the AES is true?
a. Actually, the MixColumns stage is a substitution step.
b. Actually, the ShiftRows stage provides a permutation of the data.
c. Key expansion takes 128-bit key and expands into array of 44 bit words.
d. All items.

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Recall that the simplified AES algorithm encrypts v as = T(Š(M(T(Š(v + ko))) + k1)) + k2, as described in the notes. The operations are: Add key, S-box, Shift row (T), Mix column (M), Add key, S-box, Shift row (T again), Add key. Write down an expression for the decryption of c in terms of the inverse of S (you don't need to calculate the inverse of S but, if necessary, compute the inverses of M and T).
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Answer and show all work
The ROT-13 algorithm encrypts a string one character at a time by adding 13 to the value of the internal representation of the character. We want our encryption scheme to cover the entire printable ASCII range. After examining the ASCII character set and their internal representations, we see that characters 0 through 32 and character 127 are control characters. Technically, characters 32 (space) and 127 (DEL) are printable, but we don’t want to include them in our encryption routine. Therefore, we want our encrypted string to only contain characters in the range of 33 through 126. As an example: Plaintext: Norwich Ciphertext: [|!&vpu The internal representation of ‘N’ is 78. 78 plus 13 is 91, which is the character ‘[‘. The internal representation of ‘o’ is 111. 111 plus 13 is 124, which is the character ‘|’. The internal representation of ‘r’ is 114. 114 plus 13 is 127. Since 126 is our maximum value for our desired printable range, we…
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