Complete the two questions as required by the PDF.（Just below 2 question）
Keep it original.
1、Consider the shift cipher, where we have the following distribution over the message space M:
Pr[M = a] = 0.7 and Pr[M = z] = 0:3: Here M is the random variable denoting the plaintext. What
is the probability that the ciphertext is c? What is the probability that message z was encrypted,
given that we observe the ciphertext c ?
2、Let |G(s)| = `(|s|) for some `. Consider the following experiment:
The PRG indistinguishability experiment PRGA,G(n):
(a) A uniform bit b ∈ {0, 1} is chosen. If b = 0 then choose a uniform r ∈ {0, 1}
`(n)
; if b = 1 then
choose a uniform s ∈ {0, 1}
n and set r := G(s).
(b) The adversary A is given r, and outputs a bit b’.
(c) The output of the experiment is defined to be 1 if b’ = b, and 0 otherwise.
Provide a definition of a pseudorandom generator based on this experiment, and prove that your
definition is equivalent to the definition discussed in class (See slide titled Pseudo Random Number
Generator: Definition ) (That is, show that G satisfies your definition if and only if it satisfies the
definition discussed in the class.)
0 comments