Each layer has its own subkey which is derived from the main 56-bit key by using a key scheduler.ħ. 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. Those two blocks are sent through the entire system using criss-cross which is known as the Feistel system. First the data is sent into the system and then divided into two 32-bit blocks. How many bits are there for random bits and error detection bits in the case of DES block ciphers?Ĭlarification: DES is a symmetric system that uses block ciphers which consist of 56 random bits, and 8 more bits are used for error detection.
These pseudo-random sequence are the outputs of a generator given an initial seed which is a number used to initialize a pseudo-random number generator.Ħ. As the random sequence is not possible, a pseudo-random sequence is used. The input plaintext is encrypted one byte at a time incrementally. _ uses the concept of pseudo-random sequence.Ĭlarification: The stream cipher is the one-time pad that uses the XOR function on the plaintext with a pseudo-random sequence.
TIn current cryptomeric systems, the messages that are larger than one block long that need to be split up into smaller messages by using a process called Electronic Code Book (ECB).ĥ. They operate on blocks of bits at a time and so it is termed as block ciphers. Electronic Code Book process is used in _Ĭlarification: The block cipher takes a plaintext in the chuck of bits and the bits of key are used to produce bits of ciphertext. Hence, after decrypting every bit in the cipher text, the original message will be 110100.Ĥ. When there will be a chance to decrypt the 7 th bit of the cipher text, XOR it with the first bit of the secret key. As, the cipher text is longer than the secret key, wrap around the remaining cipher text and begin again at the starting. What will be the decrypted cipher when the original message is 010010011.Ĭlarification: In order to decrypt the given cipher text, we need to XOR each bit with the corresponding bit in the secret key. Suppose in order to get a message across enemy lines, we need to choose an initial secret key say, 100110. Then, it uses again to take that ciphertext and turn it back into the password.ģ.
For example, a symmetric algorithm will use the key to encrypt some plaintext information like a password into a ciphertext. There is no secret key in case of _Ĭlarification: A symmetric algorithm uses the same key to encrypt data as well as to decrypt data. These algorithms are used in RSA encryption and public-key cryptography in which the public key is used to encrypt data and the private key is used to decrypt data.Ģ. _ is an example of asymmetric ciphers.Ĭlarification: The asymmetric ciphers use asymmetric algorithms that use one key to encrypt data and a different key to decrypt ciphers. Discrete Mathematics Multiple Choice Questions on “Cryptography – Ciphers”.ġ.