I am reading a book on cryptography and the author states that one of the complaints of the research community was that DES key length was chosen to be too short.
I am trying to depict how DES would look like if the key was 128 bits instead of 56(64) and why it would be more secure. I managed to express some ideas, but I am not sure how to evaluate them.
Expansion Permutation Effect: If the key length used after Expansion Permutation E(R-1) is increased, than R-1 expands to more bits (and then hashes with longer subkey). This means that the diffusion is greater.
Less overlapping in key scheduling: Key length also affects how key scheduling is executed. A longer key length means that shifts can be greater but I am not sure how this affects security.
I'd love to hear an authoritative answer to my pondering. Have I missed something?
In 4 rounds, a single left shift occures, in other 12, 2 bits are shifted in each of the key halfs.