Diffusion
Diffusion is Shannon’s cipher-design principle that every plaintext and key bit should influence as many ciphertext bits as possible, spreading out statistical structure.
Purpose
It spreads local changes globally through permutation and linear mixing (e.g., MixColumns), eliminating statistical redundancy of the plaintext.
Mechanism
Operations such as P-boxes, ShiftRows, and MixColumns make a 1-bit plaintext change affect all ciphertext bits after several rounds. AES MixColumns achieves efficient diffusion by mixing columns over GF(2^8).
Use cases
- Block-cipher design principle
- AES MixColumns
- Cryptographic theory