21 Questions
What is the main advantage of the Cipher Block Chaining (CBC) mode of operation over the Electronic Codebook (ECB) mode?
CBC mode is more secure against repetitive patterns in the plaintext, as each ciphertext block depends on all previous message blocks.
Which of the following is a key design principle of the Feistel cipher structure used in DES?
The F-function should be a complex, nonlinear transformation to introduce confusion and diffusion.
How can the decryption operation in a Feistel cipher be performed?
By applying the same round function in reverse order, but with the subkeys used in reverse order.
What is the key size used in the Data Encryption Standard (DES)?
56 bits
Which of the following attacks can exploit the fact that the calculations in a cipher implementation can take varying times depending on the value of the inputs?
Timing attack
How are the subkeys generated in the Data Encryption Standard (DES)?
The subkeys are generated by dividing the original 56-bit key into two 28-bit halves and applying a series of shifts and permutations to each half.
Which of the following is not a Feistel cipher design principle?
Simpler round function design is preferred for faster software en/decryption
In the Feistel cipher structure, how is the right half of the input block updated in each round?
Ri = Li-1 XOR F(Ri-1, Ki)
What is the purpose of the Initial Permutation (IP) in the DES algorithm?
To rearrange the order of the input data bits
Which of the following is not a component of the DES round function F(R,K)?
XOR with the 48-bit subkey
What is the purpose of the 'autoclaving' (autokeying) feature in the DES S-boxes?
To make the selection of the S-box row depend on both the data and the key
What is the purpose of the DES key schedule?
To generate the 16 subkeys used in the DES rounds
What is the purpose of the Feistel cipher structure in the DES algorithm?
To ensure that decryption is the inverse of encryption
What is the main reason for the controversy surrounding the choice of a 56-bit key size in the DES algorithm?
It was too small to provide adequate security
What is the 'avalanche effect' in the context of the DES algorithm?
The property where a small change in the plaintext or key produces a significant change in the ciphertext
What was the main motivation behind the development of the Feistel cipher structure, as described in the text?
To approximate a simple substitution cipher with a more complex product cipher
What is the main reason why Double-DES is not recommended for use?
Double-DES is susceptible to a meet-in-the-middle attack that can break it in $O(2^{56})$ steps.
How does the encryption process of Three-Key Triple-DES differ from Two-Key Triple-DES?
Three-Key Triple-DES is more secure than Two-Key Triple-DES, as it avoids even the potential attacks on Two-Key Triple-DES.
What is the key property of Feistel ciphers that allows for efficient decryption?
Feistel ciphers have a specific structure that makes the encryption and decryption operations equivalent in terms of security.
Which of the following is a key design principle of Feistel ciphers?
Feistel ciphers should use a balanced network structure, with equal-sized left and right halves.
What is the key difference between the subkey generation process for single-DES and Triple-DES?
Single-DES generates subkeys from a single 56-bit key, while Triple-DES generates subkeys from either two or three 56-bit keys.
Learn about Claude Shannon's introduction of the idea of substitution-permutation (S-P) networks in 1949, which formed the basis of modern block ciphers. Discover how S-P networks are based on the two primitive cryptographic operations: substitution and permutation.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
