Fistel ciphers (a) Descibe an algorithm for the decryption process for a cipher text input c = (mr,mr+1). You should use a notation similar to the encryption procedure as describe above. (b) Draw a figure for your decryption algorithm

Feistel ciphers Consider a Feistel cipher with r rounds and n 128 (half the block length); 256 (the key bit size). Then M = {0.1}256 (the plaintext space), C = {0.1}256 (the ciphertext space), and K 056 (the key space). A key scheduling algorithm determines subkeys ki,k2 from a key {0,1}256. Each subkey ki determines a function fi : {0.1}128 (0,1}128 Encryption takes r roundds: Plaintext is m(mo, m), where mo, m1 E [0,1)128 Round 1: (mo ,m11) (mi, m2), where m2 = mo f1(rni). Round 2: (ml,m2) (m2, m.3), where m3 = mih(m2). Round r: (mir-1, m.) (mr, mr+1), where mr+,-mr-1 f(mr). The ciphertext is c = (mr, mr+1). (a) Describe an algorithm for the decryption process for a ciphertext input c = (mr, mr+1). You should use a notation similar to the encryption procedure as described above. (b) Draw a figure for your decryption algorithm. Feistel ciphers Consider a Feistel cipher with r rounds and n 128 (half the block length); 256 (the key bit size). Then M = {0.1}256 (the plaintext space), C = {0.1}256 (the ciphertext space), and K 056 (the key space). A key scheduling algorithm determines subkeys ki,k2 from a key {0,1}256. Each subkey ki determines a function fi : {0.1}128 (0,1}128 Encryption takes r roundds: Plaintext is m(mo, m), where mo, m1 E [0,1)128 Round 1: (mo ,m11) (mi, m2), where m2 = mo f1(rni). Round 2: (ml,m2) (m2, m.3), where m3 = mih(m2). Round r: (mir-1, m.) (mr, mr+1), where mr+,-mr-1 f(mr). The ciphertext is c = (mr, mr+1). (a) Describe an algorithm for the decryption process for a ciphertext input c = (mr, mr+1). You should use a notation similar to the encryption procedure as described above. (b) Draw a figure for your decryption algorithm