24 does not have an additive inverse in mod 60.

10

12

36

DES is a Feistel cipher.

DES encryption and decryption require different algorithms.

All DES rounds are identical.

DES uses a 64-bit long key in 16 rounds.

If we chain two DES encryptions together, the Initial permutation IP and reverse initial permutation, IP^-1, cancel each other out, thereby weakening security.

This is for historic reasons. In fact, encrypting three times would be more secure than encrypting, decrypting, and then encrypting again

Hardware optimization is easier in the case of alternating encryption and decryption, i.e., using EDE instead of EEE.

This allows 3DES to be backwards compatible to 1DES.

0 bit in and 1 bit in

0 bit in and about half the bits in

1 bit in and about half the bits in

about half the bits in and again about half the bits in