Inside des cleartext DES is a feistel network with -16 rounds 64 bit cleartext blocks 56 bits key 16-round -f,,, f,16 derived from key i--+Feistel Network Initial permutation n(public) Decryption Apply 16, .,,(in reverse order) Same chip ciphertext 99 Inside DES DES is a Feistel network with – 16 rounds – 64 bit cleartext blocks – 56 bits key – f1 , …, f16 derived from key – Initial permutation p (public) – Decryption • Apply f16, …, f1 (in reverse order) • Same chip cleartext ciphertext 16-round Feistel Network p p -1 key 64 64 64 64 56