In a variant of DES with a 48*16 = 768-bit key, the sixteen 48-bit round keys scheduled for successive rounds in the encryption process for DES are replaced in this variant by successive 48-bit blocks of the 768-bit key.
- What are the weak keys for this variant of DES, i.e. the keys for which encryption and decryption give the same transformation on input blocks?
- What are the semi-weak key pairs, i.e. the pairs $k_1, k_2$ of keys for which encryption with $k_1$ is the same transformation as decryption with $k_2$?