I am trying to understand the sponge construction, and in the official web site I found this sentence:
The last c bits of the state are never directly affected by the input blocks and are never output during the squeezing phase.
Now I understood that the capacity is used to hide the internal state to an attacker. But I can not understand two aspects:
- How is the capacity filled?
- If it is part of the internal state, how can be possible that is not affected by the input blocks?