Types of Ciphers

Question 1

Stream Cipher

Answer 1

• plaintext digits + key stream (pseudorandom cipher digit stream)
• each plaintext digit is encrypted one at a time

Question 2

Block Cipher

Answer 2

• applied to block of data (e.g. 64 contagious bits)

- at once as a group (NOT one bit at a time)

Question 3

Substitution Cipher

Answer 3

• random bit string (nonce)
• same length as block size XoRed with message
• IVs used to create unique cipher text every time

Question 4

Transposition Cipher

Answer 4

algorithm used to rearrange letters

Question 5

What kind of cipher are the following three?

• Caesar
• Vigenere
• One-Time Pad

Answer 5

Stream Cipher

Question 6

What is the difference between the following three stream ciphers?

• Caesar
• Vigenere
• One-Time Pad

Answer 6

Key length

Question 7

Key length of the Caesar shift cipher

Answer 7

1

Question 8

Key length of the Vigenere cipher

Answer 8

longer than Caesar: usually a word or a sentence

Question 9

Key length of One-time pad

Answer 9

as long as the message itself

Question 10

Success Factors of the One-time pad

Answer 10

• key must be generated randomly (no known pattern)
• key must be at least as long as the message itself
• pad must be protected against disclosure
• must be used only ONE time and then discarded