Secure PRGs and PRFs Relationship Quiz
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Questions and Answers

What can be constructed using secure PRFs and vice-versa?

  • Random number generators
  • Secure PRGs (correct)
  • Secure encryption algorithms
  • Cryptographically insecure functions

    • In the context of computing the square root of x^2, what can be learned with only probability 1/2?

  • Both +x and -x as roots
  • The sign of exact x (correct)
  • The square root of x^2
  • The exact x

    • Which of the following is true about single message and multi-message CPA-security?

  • They have no relationship
  • Single message CPA-security is stronger
  • Multi-message CPA-security is stronger
  • They are equivalent (correct)

    • How can a secure PRF be constructed from a PRG using the tree-construction?

    <p>By fixing the input of the function to always 0</p> Signup and view all the answers

    What is a requirement for the length of plaintext in CBC mode encryption?

    <p>It should be a multiple of the block length</p> Signup and view all the answers

    What is a characteristic of the stateful variant of Counter mode compared to OFB mode?

    <p>Secure in Counter mode, insecure in OFB mode</p> Signup and view all the answers

    Which of the following is a characteristic of a secure PRG?

    <p>The outcome of the PRG is computationally indistinguishable from a true random generator</p> Signup and view all the answers

    Which statement about PRGs is false?

    <p>A computationally unbounded adversary can determine the seed</p> Signup and view all the answers

    What is the primary purpose of a Pseudo-Random Generator (PRG)?

    <p>To provide security against computationally bounded adversaries</p> Signup and view all the answers

    Why is the output of a PRG considered deterministic?

    <p>Because it relies on the seed and a deterministic function</p> Signup and view all the answers

    In what way does a PRG aim to overcome the limitations posed by perfect security?

    <p>By allowing encryption of long messages with short keys</p> Signup and view all the answers

    What does an 'efficient' adversary refer to in the context of cryptographic schemes?

    <p>An adversary with almost infinite computational resources</p> Signup and view all the answers

    Which of the following is a secure PRG according to the text?

    <p>G1 (s) = G(s1 ) ⊕ G(s2 ), where s = s1 ||s2 , and each si ∈ {0, 1}n</p> Signup and view all the answers

    What is the probability distribution of G3 (s) in relation to a true random number generator?

    <p>Always all zeros</p> Signup and view all the answers

    Why is G2 not considered a secure PRG according to the text?

    <p>First and second half of the output are the same</p> Signup and view all the answers

    What does G4 do with the parity bit of s in relation to a secure PRG?

    <p>Appends it to the output</p> Signup and view all the answers

    In the context of PRGs, why is XOR of two random/pseudorandom strings significant?

    <p>Produces another random/pseudorandom string</p> Signup and view all the answers

    What is the significance of concatenation operation in the context of secure PRGs?

    <p>Creates predictable patterns</p> Signup and view all the answers

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