CNS Quiz IT 7a

DES (Data Encryption Standard) is a symmetric encryption algorithm that operates on blocks of data. It consists of an initial and final permutation block, which rearranges the bits of the input data. The algorithm also includes a series of rounds, where each round performs a combination of substitution and permutation operations on the data. The correct answer is 16, indicating that DES has 16 rounds in total.

The given answer is the positions of the rounds in which the left shift operation is performed on the key by one bit in the DES algorithm. In round 1, the left shift is performed, followed by round 2. After that, there is a gap until round 9 where the left shift is performed again, and finally, in round 16, the left shift operation is done.

Feistel is the correct answer for the block cipher structure in DES. The Feistel structure is a symmetric structure that divides the input block into two halves and applies a series of rounds to each half. In each round, the right half is combined with a subkey and then passed through a round function. The output of the round function is then XORed with the left half. This process is repeated for multiple rounds, with the final output being the encrypted block. DES (Data Encryption Standard) is a widely used symmetric-key algorithm that employs the Feistel structure.

DES (Data Encryption Standard) uses a key generator to generate sixteen 48-bit round keys. These round keys are derived from the original 64-bit key through a process known as key schedule. Each round key is used in the encryption process to perform a series of substitution and permutation operations on the data. The use of multiple round keys enhances the security of the encryption algorithm by introducing complexity and making it harder for an attacker to decipher the encrypted data.

In DES, S-box substitution is a process that accepts 48 bits from the XOR operation. The S-boxes in DES are used to perform a non-linear substitution on the input data. Each S-box takes a 6-bit input and produces a 4-bit output. This substitution process adds an additional layer of confusion and increases the security of the encryption algorithm.

In a single round of a Feistel cipher, the P-box will execute 2 times. The P-box, also known as the permutation box, is a component of the Feistel cipher that permutes the input bits to create a confusion effect. In each round, the input is divided into two halves, and the P-box is applied to one of the halves. This process is repeated twice, once for each half, resulting in a total of 2 executions of the P-box in a single round of the Feistel cipher.

The correct answer is "All" because all three expressions are valid for encryption or decryption using two-key 3-DES. The first expression shows encryption followed by decryption using key K1 and K2. The second expression shows decryption followed by encryption using key K1 and K2. The third expression shows encryption followed by decryption using key K2 and K1. Therefore, all three expressions are correct for encryption or decryption using two-key 3-DES.

A truly weak key is a key that does not provide any security and can easily be exploited to retrieve the original plaintext. In this case, the statement "D ( K, ( D ( K, C ) ) = C" is true for a truly weak key. This means that decrypting the ciphertext twice with the same key will result in the original plaintext, indicating that the encryption process is ineffective and the key is weak.

The DES algorithm uses a total of 8 S-boxes. Each S-box takes a 6-bit input and produces a 4-bit output. Since the DES algorithm operates on 64-bit blocks, it requires a total of 8 S-boxes to process all the bits in the block. Therefore, the correct answer is 8.

The most prominent reason to consider 2-DES as an insecure cipher option is the availability of contemporary high-speed machines. With the advancement in technology, modern machines have become capable of performing computations at a much higher speed, making it easier to break the encryption used in 2-DES. This renders 2-DES vulnerable to attacks and compromises its security.