Which property spreads plaintext influence across ciphertext?

• A. Confusion
• B. Diffusion
• C. Padding
• D. ECB Mode

Answer: (B)

Diffusion is the property that ensures the influence of each plaintext bit is spread across many ciphertext bits, so a small change in plaintext leads to a large, widespread change in the ciphertext. This is the avalanche effect in action: after mixing and transforming across rounds, every output bit depends on many input bits, destroying simple patterns and making statistical analysis of the ciphertext difficult. In practice, diffusion comes from the way modern ciphers mix data through multiple rounds of substitution and permutation, so a single bit flip propagates widely.

Confusion, by contrast, hides the relationship between the key and the ciphertext, not how plaintext changes affect the ciphertext overall. Padding simply adds extra bits to fit block sizes, it’s about block alignment, not spreading plaintext influence. ECB Mode is a mode of operation that can fail to diffuse across blocks, as identical plaintext blocks yield identical ciphertext blocks, revealing patterns.