Question regarding Exercise 9 Question 3 (1c)

Question

There are two possible interpretations of this question and that may have impact on the correct answer.

Interpretation one: Not provided by signatures alone

Interpretation two: Imposible once signatures are in use (So which features become fundamentally unachievable as soon as you insist on using signatures)

My question is which interpretation of the exercise question should I use to solve this question?

Thanks in advance

Answer 1

I'm not sure that I understand your second interpretation, but your first one sounds correct. I would rephrase the original question as:

“Which security property cannot be achieved by using signatures?”