1) Suppose a message is first encrypted with Alice’s public key, and then a signature of this encryption result is produced using Bob’s private key. The encrypted message and the signature are then sent. Which of the following is true?
A. The recipient can be certain that the sender is Alice
B. The recipient can be certain that the sender is Bob
C. The recipient should decrypt the message with Bob’s private key
D. The recipient should verify the signature with Alice’s public key iv.
2) Which of the following is NOT a desired property of a good cryptographic hash function h?
A. There is exactly one output h(x) for each input x.
B. The output h(x) appears to have no resemblance to the input x.
C. If two inputs x and y are similar then the outputs h(x) and h(y) are also similar.
D. It is computationally difficult to work out which input x produces a given output h(x).
3) Suppose h is a strong cryptographic hash function where the outputs are always 32 hexadecimal characters. Which among the following four actions is the most computationally difficult?
A. Find a string x so that h(x) = 00000000000000000000000000000000
B. Find a string x so that h(x) begins with 0000000000000000
C. Find two different strings x and y so that h(x) = h(y)
D. Find two different strings x and y so that h(x) and h(y) shares the same first 16 hexadecimal characters
4). To perform a dictionary attack against a dictionary of size 10000 where a salt of 32 bits is used, the number of hash computations needed is approximately A. 320000 B. 1000032 C. 2 32 ×10000 D. 2 32×10000 vii. If A issues a certificate that contains B’s public key, then the certificate should be signed with
A. A’s private key
B. A’s public key
C. B’s private key
D. B’s public key
5. Some cryptographic algorithms rely on the computational difficulty of obtaining y given the values of x, z and x y mod z (for some appropriate choices of x and z). This is known as
A. the RSA problem
B. the discrete logarithm problem
C. the factorisation problem
D. the modular exponentiation problem