Cryptography Confusion

B"H

JD, I am trying to get my heard around cryptography's use of the term "confusion." Conrad writes: ""confusion means that the relationship between the plaintext and the ciphertext should be as confused (or random) as possible."

Online I found a paper here: http://www.nku.edu/~christensen/diffusionandconfusion which states: "Confusion means that the key does not relate in a simple way to the ciphertext. In particular, each character of the ciphertext should depend on several parts of the key."

I don't "get" it...the cipher text is supposed to seem"random" relative to the plain text...but somehow there is still a static relationship between each character in the cipher text and the characters of the plain text...huh?

Thanks!
Dovid

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Comments

TechGuy215

The overall goal of confusion is to make the relationship between the statistics of the ciphertext and the value of the encryption key as complex as possible, making it EXTREMELY difficult to discover the key. Therefore 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 typically achieved by the use of a complex substitution algorithms.

lsud00d

I believe you are taking the 'depend on' too literally in this situation in that it's not a 'static' relationship as you ask...it's a dependent relationship meaning the characteristics of the key will affect the resultant ciphertext. The increased complexity in the key (algorithm), the increased confusion (randomness) between it and the ciphertext.

Chassidic1

Thanks guys :-]

cyberguypr

My attempt at an oversimplified illustrated version of this:

Plaintext: HITHEREWORLD
CIPHER: ABC123456789
CIPHERTEXT: XSWALG456789

See how part of the ciphertext is closely related to part of the cipher? Not very random at all.

If on the other hand the resulting ciphertext were XSWALGSTLRO, then there's no discernible relationship at all.

JDMurray

Confusion is also demonstrated when extreme changes result in cipher text when only small changes are made to the original plain text. For example, if you encrypt a plain text of the Declaration of Independence, then change the first characters of the plain text from "Four" to "Five" and re-encrypt it, the second set of cipher text will look very different from the first despite there being only a very small difference between the original and the changed plain text.

Chassidic1

Thanks again guys, I appreciate your taking the time to help me out with your examples.