Let consider the following protocol

• Anna has a 128-bit random string b
• Tom wants to prove that he knows b
• Tom sends a 128-bit string b' to Anna
• Anna accepts if b = b', otherwise reject

Is this an interactive proof?

1: No, because it is not complete

2: No, because it is not sound

3: No, because the proof cannot be verified in polynomial time

4: Yes it is.