What's the difference between substitution and permutation in DES? From my understanding substitution is replacing the data with new data and permutation is just rearranging the data?
You pretty much answered your own question:
- Substitution replaces a section of data with another chunk of data
- Transposition moves data from one place to another
Substitution is usually responsible for non-linearity or "confusion", while transposition is useful for "diffusion" and ensuring that changes in one bit propagate to the rest of the state.