DES Modes

Question 1

ECB - Electronic Code Book

Answer 1

• simplest & least secure
• 64 bit blocks processed
• same block –> same encrypted block –> easy to break

Question 2

CBC - Cipher Block Chaining

Answer 2

• each block of plain text is XORed
• with previous block of cipher text
• reverses XOR operation

Question 3

CFB - Cipher Feedback

Answer 3

• streaming version of CBC
• real time
• memory buffers of same block size
• when data is full: encrypted + transmitted
• uses chaining –> more errors

Question 4

OFB - Output Feedback

Answer 4

• operates similar to CFV, but XORs with seed value

- no chaining –> less errors

Question 5

CTR - Counter

Answer 5

• incrementing counter instead of seed

- errors doe not propagate