Question

How many bits are there for random bits and error detection bits in the case of DES block ciphers?

(a) 72, 1024

(b) 56, 8

(c) 104, 45

(d) 32, 198

The question was posed to me in unit test.

This intriguing question originated from Cryptography in division Number Theory and Cryptography of Discrete Mathematics

Answer 1

The correct answer is (b) 56, 8

Easy explanation: DES is a symmetric system that uses block ciphers which consist of 56 random bits, and 8 more bits are used for error detection. First the data is sent into the system and then divided into two 32-bit blocks. Those two blocks are sent through the entire system using criss-cross which is known as the Feistel system. There are 16 layers in DES. At each layer, one half of the data passes through the Fiestel function and after its completion, it is XORd with the other half of the data. Each layer has its own subkey which is derived from the main 56-bit key by using a key scheduler.