Which term refers to the technique of keeping the relationship between ciphertext and the statistical frequencies of the plaintext concealed?

The term that refers to the technique of keeping the relationship between ciphertext and the statistical frequencies of the plaintext concealed is known as confusion. This concept is integral to cryptography, as it helps to obscure the connection between the plaintext and the ciphertext.

Confusion aims to make the statistical analysis of the ciphertext challenging, effectively hiding patterns in the plaintext from being discerned. This is accomplished through substitution methods or complex encryption algorithms that jumble the data, making it difficult for an attacker to derive meaningful information even if they have access to the ciphertext.

In the context of other terms, diffusion relates to spreading the influence of a single plaintext symbol over several ciphertext symbols, thereby ensuring that changes in plaintext affect the ciphertext in more drastic ways. While the avalanche effect is a principle where small changes in the plaintext produce significant and unpredictable changes in the ciphertext, it does not specifically address the concealment of statistical relationships. Clustering generally pertains to grouping similar data, which does not apply to the concept of concealing relationships in encryption.