Which of the following BEST describes the security offered by the Diffie-Hellman key-exchange protocol (assuming the DDH problem is hard)?

What is the size of key space |K| for a byte-wise shift cipher, considering the message space as English alphabets, and encryption algorithm as Enc​(m)=(m⊕k)?

Let G be a function mapping n-bit inputs to 2n-bit outputs. Which of the following is true of the pseudo one-time pad encryption scheme based on G?

Define the generator G by G(x) = x | x. (G maps inputs of length n to outputs of length 2n). Which of the following algorithms A distinguishes the output of G from uniform?

Three ASCII messages containing English letters and spaces only are encrypted using the one-time pad and the same key. The 10th byte of the first ciphertext is observed to be 0x66, the 10th byte of the second ciphertext is observed to be 0x32, and the 10th byte of the third ciphertext is observed to be 0x23. Let m1 (resp., m2, m3) denote the 10th ASCII character in the first (resp., second, third) message. What is the most you can conclude about m1, m2, and m3?

For the byte-wise shift cipher where the key space is {0, …, 255}. What is Pr[K = 2]?

Which of the following problems is hard if the RSA assumption holds? In all the below, N is a product of distinct, large primes p and q, and e is relatively prime to ϕ(N).

What is the value (in decimal) of 0x48?

If the message “cryptoisfun” is encrypted with the shift cipher and key 25. What is the resulting ciphertext?

Which of the following is a drawback of the private-key setting that is NOT addressed by the public-key setting?