If different keys generate the same ciphertext for the same message, what is this called?
A.
Collision
B.
Secure hashing
C.
MAC
D.
Key clustering
Explanation:
Message A was encrypted with key A and the result is ciphertext Y. If
that same Message A was encrypted with key B the result should not be ciphertext Y.
The ciphertext should be different since a different key was used. But if this does
take place it is referred to as key clustering.
In cryptography, key clustering is said to occur when two different keys generate the same ciphertext from the same plaintext, using the same cipher algorithm. A good cipher algorithm, using different keys on the same plaintext, should generate a different ciphertext, irrespective of the key length.
Assume that there is a plaintext P, two different keys, K1 and K2, and an algorithm A. Ciphertexts C1 and C2 with the two keys are generated as follows:
P → A(K1) → C1
P → A(K2) → C2
C1 should not equal C2, if they do then key clustering has occurred.