Key clustering

Key Clustering

Ciphertext is the result of encrypting plaintext using a key. Ciphers (or algorithms) are used to encrypt the plaintext using keys. A good algorithm, using different keys on the same plaintext generates a different ciphertext, irrespective of the key length.

Let us assume that I have a plaintext P, two keys (of same length, assumed for simplicity) K1 and K2, and an algorithm A. I will generate ciphertexts C1 and C2 with the two keys as follows

P -----A(K1)------> C1

P -----A(K2)------> C2

This might not always be the case. I could have possibly gotten C1 ciphertext in Case 2 as well. That would be Key Clustering.

For the sake of definition, key clustering is when two different keys generate the same ciphertext from the same plaintext, using same or different algorithm.