**1) What is the meaning of one-way function?**

a. It can be used by the sender but not by the receiver.

b. It can be used by the receiver but not by the sender.

c. It implements a many-to-one mapping.

d. It implements a one-to-many mapping.

**Answer:** c

**Solution: **Hashing is a type of one-way function, which refers to a function that implements a many-to-one mapping. Several different messages may map to the same hash value, but the converse is not true. The correct option is (c).

**2) Which of the following are examples of hash functions?**

a. MD5

b. Triple-DES

c. SHA-1

d. All of these.

**Answer:** a, c

**Solution:** MD5 and SHA-1 are examples of hash function, while Triple-DES is used in encryption. Thus the correct options are (a) and (c).

**3) In terms of speed (slowest to fastest), which of the following orders are correct?**

a. Hash computation, Public-key encryption, Symmetric-key encryption

b. Public-key encryption, Symmetric-key encryption, Hash computation

c. Symmetric-key encryption, Public-key encryption, Hash computation

d. None of these.

**Answer:** b

**Solution:** Computation of hash function is the fastest, which computation of public-key encryption is the slowest. Symmetric-key encryption lies in between the two. Hence, the correct option is (b).

**4) The hash digest length of SHA-256 is ***__* bits.

**Answer: **256

**Solution:** The size of the hash digest or the number of bits in the hash for SHA-256 is 256 bits. This follows from the definition of SHA-256.

**5) What is birthday attack?**

a. It is an attack on public-key cryptography.

b. It is an attack on symmetric-key cryptography.

c. It is an attack on hash functions.

d. None of these.

**Answer:** c

**Solution:** Birthday attack utilizes some statistical properties to mount attacks on hash functions. The correct option is (c).

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