In diffusion, the statistical structure of the plaintext is
dissipated into long-range statistics of the ciphertext. This is
achieved by having each plaintext digit affect the value of many
ciphertext digits, which is equivalent to saying that each
ciphertext digit is affected by many plaintext digits. Confusion
seeks to make the relationship between the statistics of the
ciphertext and the value of the encryption key as complex as
possible, again to thwart attempts to discover the key. Thus, even
if the attacker can get some handle on the statistics of the
ciphertext, the way in which the key was used to produce that
ciphertext is so complex as to make it difficult to deduce the key.
This is achieved by the use of a complex substitution
algorithm.
