Secure channels

Question 1

mention 3 possible protocol designs of mac and encryption algorithm and explain them.

Answer 1

MAC then ENC - ENC k-enc(m,MAC k-int(m)) not safe when the hash is weak

MAC and ENC - ENC k-enc(m), MAC k-int(m) same thing, the weakest between all

ENC then MAC - ENC k-enc(m) , MAC k-int(ENC k-enc(m) - best option

Question 2

What is AEAD? what are its advatanges?

Answer 2

authenticated encryption with associated data.
One pass encryption and MAC calculation for payload including “associated data”

Advanatges:
1.algorithms correctly combine message encryption and authentication and are standarized.
2.AEAD needs one pass over the data.

Question 3

Name 2 attacks against secure channel and explain them.

Answer 3

1.Re-Use of Initialization Vector:
when using same IV, we will get to a point where if we XOR both encrypted messages which were encrypted with the same IV vector, the value will be equal to the xored plain texts of the same messages. If one plaintext is known, then we can know the other plaintext.
2. padding oracle attack