Question

modes. + There cise 4 different types o Block cipher with their advantages and disadvantages? compare diferent block capher modes 2. you need to do some research on dofferent types of cryptagraphy libranes on Python. how can we use cryptography Hibranes on Python. While down the steps to install cryptography library in Python. Write a program then cry hot and decng pt a Message using Python library

Answer 1

A block cipher is an encryption algorithm that calls the fixed size of the input as C bits and then constructs the ciphertext of the C bits. If the input is larger than C bits it can be further divided.

Electronic Code Book (ECB) - The easiest block cipher mode of functioning is an electronic codebook. It is easier because of direct encryption of each block of input plaintext and output is in form of blocks of encrypted ciphertext.

Advantages -

1. Simple method of a block cipher.

2. Parallel encryption of blocks of bits is possible, thus it is a faster method of encryption.

Disadvantages-

1. There is a risk of cryptoanalysis from having a direct connection between plaintext and ciphertext.

Cipher Block Chaining – Cipher block chining or CBC is an advancement over the ECB because the ECB compromises certain security requirements. In CBC, the previous cipher block is given as input to the next encryption algorithm after XOR with the original plaintext block.

Advantages -

1. CBC is a good authentication mechanism.

2. CBC works well for input greater than c bits.

Disadvantages-

1. Parallel encryption is not possible because every encryption requires a previous cipher.

Cipher Feedback Mode (CFB) – In this mode, the cipher is given as feedback for the next block of encryption with some new specifications: first an initial vector IV is used for first encryption and output bits are divided as set of s and b-s bits the left-hand side s bits are selected and are applied an XOR operation with plaintext bits. The result given as input to a shift register and the process continues.

Advantages -

1. Since, there is some data loss due to the use of the shift register, it is difficult to implement cryptoanalysis.

2. Save our code from external users.

Disadvantages-

1.The CPU is not free during the entire process of ciphertext.

Output Feedback Mode – It involves feeding back sequential output blocks from the underlying block cipher. These response blocks provide strings of bits to feed the encryption algorithm that act as a key-stream generator in the case of CFB mode.

Advantages -

1. Bit errors in transmission do not propagate to encryption.

Disadvantages-

1. It is more vulnerable to a message flow modification attack than a CFB in mode of operation.