HW6 Q3a

HW6 Q3a

Evyatar (guest) 05 Feb 2018 14:43

In Question 3 about CCA-security, we have to prove the difference between two probabilities is negligible.
I think there is a mistake in the second term, and it should be $f_n(m')$ instead of $f_n(m)$.

Evyatar (guest) 05 Feb 2018 19:32

It's actually much easier the way it is stated in the HW now, so I hope it was not a mistake

Re: HW6 Q3a

nbitansky 05 Feb 2018 19:34

No mistake.
The goal here is to show that the adversary cannot turn an encryption of an unknown message to an encryption of a related message.
So intuitively, we want to say that if the adversary can turn an encryption of m to an encryption of f(m), then it in fact turns anything to an encryption of f(m), which is something we may not be able to prevent.