1. If one-time pads are provably secure, why are they so rarely used in practice?
2. Prove that the DES key consisting of all 0-bits and the DES key consisting of all 1-bits are both weak keys. What are the other two weak keys? (Note: Differences in the parity bits, which the PC-1 permutation drops, do not count; the keys must differ in the 56 bits that are used to generate the key schedule.)