Exam number 1 question 3 b

Re: Exam number 1 question 3 b

Fri, 31 Jan 2020 17:23:11 +0000

Sorry but I don't understand the first part of your question. You should first make sure you understand the solution to the HW5.Q1. Then you're welcome to try and reformulate the question more clearly. As for the second part, see Ohad's answer.

(no title)

Fri, 31 Jan 2020 16:08:46 +0000

The reason for the 2|E| is because you want the prover to convince the verifier in that round with probability>1-1/|E| if the verifier chose b=0.
That happens with that probability if overall p>1-1/2|E|, because:
Pr[convince] = 0.5*Pr[convince|b=0] + 0.5*Pr[convince|b=1]

If Pr[convince] > 1-1/2|E|:

0.5*Pr[convince|b=0] > 1-1/2|E| - 0.5*Pr[convince|b=1]
Pr[convince|b=0] > 2 - 1/|E| - Pr[convince|b=1] >= 1-1/|E|

Which is what we want.

Exam number 1 question 3 b

Fri, 31 Jan 2020 14:37:18 +0000

I don't understand the first equation in the solution and maybe I'm missing a more significant part of the question here.
If we know that the prover is convincing the verifier w.p. 1/100, why do we need the other expression in some session? The prover is deterministic so I don't see the reason for the 2 probabilities.

And additionally, why is there a 2|E| instead of |E| in the denominator?

Thanks!