If the application of a hash function results in an m-bit fixed length output, an attack on the hash
function that attempts to achieve a collision after 2 m/2 possible trial input values is called a(n):
A.
Birthday attack
B.
Meet-in-the-middle attack
C.
Chosen-ciphertext attack
D.
Adaptive-chosen-plaintext attack
Explanation:
This problem is analogous to asking the question How many people must be in a room for the
probability of two people having the same birthday to be equal to 50%? The answer is 23. Thus,
trying 2m/2 possible trial inputs to a hash function gives a 50% chance of finding two inputs that
have the same hash value. Answer a, describes an attack in which the attacker can choose the
plaintext to be encrypted and can modify his/her choice based on the results of a previous
encryption. * Answer the chosen-cipher text attack is where the attacker can select different
ciphertexts to be decrypted and has the decrypted plaintext available. This attack is used to
determine the key or keys being used. Answer d is an attack against double encryption. This
approach shows that for a key length of k bits, a chosen-plaintext attack could find the key after2k+1 trials instead of 22k attempts. In this attack on double encryption, one encrypts from one end,
decrypts from the other and compares the results in-the-middle.