Week 1 - AES, Blowfish, Modes of Operation

Question 1

What is Advanced Encryption Standard (AES)?

Answer 1

uses plaintext of 128 bit blocks, applies a key of size 128 bits and uses substitution, permutation and XOR for 10 rounds operations to encrypt the data

Question 2

What steps are performed in each AES round?

Answer 2

1. SubBytes (byte substitution).
2. ShiftRows (shifting rows of the state array).
3. MixColumns (mixing the columns).
4. AddRoundKey (XOR with the round key).

Question 3

What is Blowfish?

Answer 3

It is a symmetric block cypher that uses 64 bit blocks with a 256 bit key

Question 4

How does Blowfish work?

Answer 4

uses the Feistel cipher structure, and performs operations over 16 rounds

Question 5

What is a mode of operation in block ciphers?

Answer 5

how a block cypher processes data beyond a single block to improve security.

Question 6

What is Electronic Code book (ECB)?

Answer 6

each block is encrypted seperately. however it easily reveals patterns

Question 7

What is Cipher Block Chaining (CBC) mode?

Answer 7

each block is XOR’d with the previous block

requires initialisation vector (IV) and padding

IV is a pseudo-random value