90 Questions
Which type of cipher encrypts a digital data stream one bit or one byte at a time?
Stream cipher
What is the most widely used symmetric cipher?
Data Encryption Standard (DES)
Which type of cipher treats a block of plaintext as a whole and produces a ciphertext block of equal length?
Block cipher
What is the structure referred to as a Feistel block cipher based on?
Block ciphers
Which type of cipher is also known as an additive cipher?
Caesar cipher
Which type of cipher involves both addition and multiplication operations?
Affine cipher
What type of attack can be performed on an additive cipher without human intervention to determine the possible plaintexts?
Frequency analysis attack
What type of attack can be performed on any monoalphabetic substitution cipher without human intervention to determine the possible plaintexts?
Frequency analysis attack
Which of the following is NOT a parameter that affects the Feistel cipher design?
Round function F
What is the purpose of the permutation in the Feistel cipher?
To simplify the implementation of the decryption process
What is the relationship between block size and security in the Feistel cipher?
Larger block sizes offer greater security
What is the advantage of using a larger key size in the Feistel cipher?
Greater resistance to brute-force attacks
Which of the following is true about block ciphers?
Block ciphers are more commonly used in network-based symmetric cryptographic applications than stream ciphers.
What is the ideal block cipher?
A block cipher that allows for the maximum number of possible encryption mappings from the plaintext block.
Why are small block size block ciphers vulnerable to statistical analysis of the plaintext?
Because the mapping from plaintext to ciphertext is not unique for each plaintext block.
What is the required key length for a block cipher with a block size of 4 bits?
64 bits
Which of the following is the key length required for a 64-bit block in an n-bit ideal block cipher?
64 * 2^128
What is the key size for a block substitution cipher with n = 4?
16
What is the danger with using a block substitution cipher with a mapping defined in terms of linear equations?
It may be vulnerable to cryptanalysis by an attacker who knows the structure of the algorithm
What is the Feistel cipher?
A product cipher that combines multiple simple ciphers
Which of the following is a method suggested by Shannon for frustrating statistical cryptanalysis?
Diffusion and confusion
What is the purpose of diffusion in a block cipher?
To make the statistical relationship between the plaintext and ciphertext complex
What is the effect of diffusion on the letter frequencies in the ciphertext?
They will be more nearly equal than in the plaintext
What is the structure of a Feistel cipher?
The plaintext block is divided into two halves, which pass through multiple rounds of processing and then combine to produce the ciphertext block
According to the text, what is the notation used for data traveling through the encryption algorithm?
LEi and REi
According to the text, what is the notation used for data traveling through the decryption algorithm?
LDi and RDi
According to the text, what is the relationship between the intermediate value of the decryption process and the corresponding value of the encryption process at every round?
They are swapped
According to the text, what is the output of the (16 - i)th decryption round?
LD16 - i ‘RD16 - i
According to the text, what is the output of the last iteration of the encryption process?
RE16 ‘LE16
According to the text, what is the input to the first round of the encryption process?
RE16 ‘LE16
Which type of cipher treats a block of plaintext as a whole and produces a ciphertext block of equal length?
Block cipher
What is the required key length for a block cipher with a block size of 4 bits?
8 bits
What is the relationship between block size and security in the Feistel cipher?
Block size does not affect security
What is the most widely used symmetric cipher?
Data Encryption Standard (DES)
Which type of cipher treats a block of plaintext as a whole and produces a ciphertext block of equal length?
Block cipher
What is the most widely used symmetric cipher?
Data Encryption Standard (DES)
What is the structure referred to as a Feistel block cipher based on?
Block ciphers
Which of the following is true about block ciphers?
They treat a block of plaintext as a whole and produce a ciphertext block of equal length
What is the purpose of the permutation in the Feistel cipher?
To increase the confusion of the plaintext
What is the relationship between block size and security in the Feistel cipher?
Smaller block size increases security
What is the advantage of using a larger key size in the Feistel cipher?
Increased resistance to brute-force attacks
What is the required key length for a block cipher with a block size of 4 bits?
64 bits
Which of the following is true about diffusion in a block cipher?
Diffusion makes the statistical relationship between the plaintext and ciphertext more complex.
What is the purpose of confusion in a block cipher?
To make the relationship between the statistics of the ciphertext and the value of the encryption key as complex as possible.
What is the structure referred to as in a Feistel cipher?
Feistel block cipher structure
What type of cipher involves both addition and multiplication operations?
Feistel cipher
Which of the following is a characteristic of an n-bit ideal block cipher?
The length of the key is n * 2n bits
Which of the following is NOT a parameter that affects the design of a Feistel cipher?
Round function
What is the key length required for a 64-bit block in an n-bit ideal block cipher?
1021 bits
What is the purpose of diffusion in a block cipher?
To change the statistics of the plaintext at the level of individual letters or permuted blocks
What is the danger with using a block substitution cipher with a mapping defined in terms of linear equations?
It may be vulnerable to cryptanalysis by an attacker that is aware of the structure of the algorithm
What is the relationship between block size and security in the Feistel cipher?
Larger block sizes offer greater security
What is the structure used by a number of significant symmetric block ciphers currently in use?
Feistel structure
What is the advantage of using a larger key size in the Feistel cipher?
Greater resistance to brute-force attacks
According to the text, what is the relationship between the intermediate value of the decryption process and the corresponding value of the encryption process at every round?
They are swapped
What is the output of the last iteration of the encryption process?
RE16 ' LE16
What is the input to the first round of the encryption process?
RE16 ' LE16
According to the text, what is the notation used for data traveling through the encryption algorithm?
LEi and REi
According to the text, what is the output of the (16 - i)th decryption round?
LD16 - i ' RD16 - i
What is the structure referred to as a Feistel block cipher based on?
Addition and multiplication operations
What is the main focus of this chapter on symmetric encryption?
Block ciphers
What is the maximum number of possible encryption mappings from a plaintext block in an ideal block cipher?
2^n
What is the practical problem with using a small block size in an ideal block cipher?
Vulnerability to statistical analysis
What is the required key length for a block cipher with a block size of 4 bits?
64 bits
Which type of cipher treats a block of plaintext as a whole and produces a ciphertext block of equal length?
Block cipher
What is the structure referred to as a Feistel block cipher based on?
Substitution and permutation
What is the purpose of diffusion in a block cipher?
To ensure that a change in one bit of the plaintext affects multiple bits of the ciphertext
What is the advantage of using a larger key size in the Feistel cipher?
Increased resistance to brute force attacks
What is the relationship between block size and security in the Feistel cipher?
Larger block sizes mean greater security
What is the key size for a block substitution cipher with n = 4?
8 bits
What is the advantage of using a larger key size in the Feistel cipher?
Greater resistance to brute-force attacks
What is the structure referred to as in a Feistel cipher?
Substitution-permutation network
Which type of cipher is also known as an additive cipher?
Caesar cipher
What is the purpose of diffusion in a block cipher?
To spread the influence of a single bit change in the plaintext across multiple bits in the ciphertext
What is the relationship between block size and security in the Feistel cipher?
A larger block size generally provides stronger security
What is the advantage of using a larger key size in the Feistel cipher?
Increased resistance against brute-force attacks
Which of the following is a characteristic of an n-bit ideal block cipher?
The length of the key is n * 2n bits
What is the relationship between block size and security in the Feistel cipher?
Block size and security are inversely proportional
What is the purpose of diffusion in a block cipher?
To confuse the attacker by hiding the statistical characteristics of the plaintext
What is the required key length for a block cipher with a block size of 4 bits?
256 bits
Which of the following is a characteristic of a Feistel cipher?
It treats a block of plaintext as a whole and produces a ciphertext block of equal length
What is the purpose of confusion in a block cipher?
To make the relationship between the statistics of the ciphertext and the value of the encryption key as complex as possible
What is the effect of diffusion on the letter frequencies in the ciphertext?
The letter frequencies in the ciphertext will be more nearly equal than in the plaintext
What is the structure used by a number of significant symmetric block ciphers currently in use?
Feistel cipher
According to the text, what is the notation used for data traveling through the encryption algorithm?
LEi and REi
According to the text, what is the notation used for data traveling through the decryption algorithm?
LDi and RDi
What is the output of the (16 - i)th decryption round according to the text?
REi ‘LEi
What is the output of the last iteration of the encryption process according to the text?
RE16 ‘LE16
What is the relationship between the intermediate value of the decryption process and the corresponding value of the encryption process at every round according to the text?
They are swapped
What is the purpose of the permutation in the Feistel cipher according to the text?
To increase the security
Quiz: Understanding the Round Function and Subkeys in Encryption
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