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"""Tham module provides encrypting/decrypting according AES(128) standart. Based on Rijndael algorithm, AES uses 4 transformation for encrypting: SubSytes(), ShiftRows(), MixColumns() and AddRoundKey(). For decrypting it uses inverse functions of that fout. Detales you can read here: http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf or here: http://en.wikipedia.org/wiki/Advanced_Encryption_Standard or here: http://www.cs.bc.edu/~straubin/cs381-05/blockciphers/rijndael_ingles2004.swf or somewhere else. Comments rather won't help if don't read documentation of the algorithm. """ nb = 4 # number of coloumn of State (for AES = 4) nr = 10 # number of rounds ib ciper cycle (if nb = 4 nr = 10) nk = 4 # the key length (in 32-bit words) # This dict will be used in SubBytes(). hex_symbols_to_int = {'a': 10, 'b': 11, 'c': 12, 'd': 13, 'e': 14, 'f': 15} sbox = [ 0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76, 0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0, 0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15, 0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75, 0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84, 0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf, 0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8, 0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2, 0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73, 0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb, 0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79, 0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08, 0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a, 0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e, 0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf, 0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16 ] inv_sbox = [ 0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb, 0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb, 0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e, 0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25, 0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92, 0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84, 0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06, 0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b, 0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73, 0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e, 0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b, 0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4, 0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f, 0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef, 0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61, 0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d ] rcon = [[0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36], [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00], [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00], [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00] ] def print_list(info_string, state): """Function prints state """ print(info_string) for row in state: print('[{}]'.format(', '.join(hex(element) for element in row))) print('----') return 0 def encrypt(input_bytes, key): """Function encrypts the input_bytes according to AES(128) algorithm using the key Args: input_bytes -- list of int less than 255, ie list of bytes. Length of input_bytes is constantly 16 key -- a strig of plain text. Do not forget it! The same string is used in decryption Returns: List of int """ # let's prepare our enter data: State array and KeySchedule state = [[] for j in range(4)] for r in range(4): for c in range(nb): state[r].append(input_bytes[r + 4 * c]) key_schedule = key_expansion(key) print_list('Initial state:', state); state = add_round_key(state, key_schedule) print_list('After add round key:', state) for rnd in range(1, nr): print ('===Round: ===', rnd) state = sub_bytes(state) print_list('After sub bytes:', state) state = shift_rows(state) print_list('After shift rows:', state) state = mix_columns(state) print_list('After mix columns:', state) state = add_round_key(state, key_schedule, rnd) print_list('After add round key:', state) print ('===Final round: ===') state = sub_bytes(state) print_list('After sub bytes:', state) state = shift_rows(state) print_list('After shift rows:', state) state = add_round_key(state, key_schedule, rnd + 1) print_list('After add round key:', state) output = [None for i in range(4 * nb)] for r in range(4): for c in range(nb): output[r + 4 * c] = state[r][c] return output def decrypt(cipher, key): """Function decrypts the cipher according to AES(128) algorithm using the key Args: cipher -- list of int less than 255, ie list of bytes key -- a strig of plain text. Do not forget it! The same string is used in decryption Returns: List of int """ # let's prepare our algorithm enter data: State array and KeySchedule state = [[] for i in range(nb)] for r in range(4): for c in range(nb): state[r].append(cipher[r + 4 * c]) key_schedule = key_expansion(key) state = add_round_key(state, key_schedule, nr) rnd = nr - 1 while rnd >= 1: state = shift_rows(state, inv=True) state = sub_bytes(state, inv=True) state = add_round_key(state, key_schedule, rnd) state = mix_columns(state, inv=True) rnd -= 1 state = shift_rows(state, inv=True) state = sub_bytes(state, inv=True) state = add_round_key(state, key_schedule, rnd) output = [None for i in range(4 * nb)] for r in range(4): for c in range(nb): output[r + 4 * c] = state[r][c] return output def sub_bytes(state, inv=False): """That transformation replace every element from State on element from Sbox according the algorithm: in hexadecimal notation an element from State consist of two values: 0x<val1><val2>. We take elem from crossing val1-row and val2-column in Sbox and put it instead of the element in State. If decryption-transformation is on (inv == True) it uses InvSbox instead Sbox. Args: inv -- If value == False means function is encryption-transformation. True - decryption-transformation """ if inv == False: # encrypt box = sbox else: # decrypt box = inv_sbox for i in range(len(state)): for j in range(len(state[i])): row = state[i][j] // 0x10 col = state[i][j] % 0x10 # Our Sbox is a flat array, not a bable. So, we use this trich to find elem: # And DO NOT change list sbox! if you want it to work box_elem = box[16 * row + col] state[i][j] = box_elem return state def shift_rows(state, inv=False): """That transformation shifts rows of State: the second rotate over 1 bytes, the third rotate over 2 bytes, the fourtg rotate over 3 bytes. The transformation doesn't touch the first row. When encrypting transformation uses left shift, in decription - right shift Args: inv: If value == False means function is encryption mode. True - decryption mode """ count = 1 if inv == False: # encrypting for i in range(1, nb): state[i] = left_shift(state[i], count) count += 1 else: # decryptionting for i in range(1, nb): state[i] = right_shift(state[i], count) count += 1 return state def mix_columns(state, inv=False): """When encrypting transformation multiplyes every column of State with a fixed polinomial a(x) = {03}x**3 + {01}x**2 + {01}x + {02} in Galua field. When decrypting multiplies with a'(x) = {0b}x**3 + {0d}x**2 + {09}x + {0e} Detailed information in AES standart. Args: inv: If value == False means function is encryption mode. True - decryption mode """ for i in range(nb): if inv == False: # encryption s0 = mul_by_02(state[0][i]) ^ mul_by_03(state[1][i]) ^ state[2][i] ^ state[3][i] s1 = state[0][i] ^ mul_by_02(state[1][i]) ^ mul_by_03(state[2][i]) ^ state[3][i] s2 = state[0][i] ^ state[1][i] ^ mul_by_02(state[2][i]) ^ mul_by_03(state[3][i]) s3 = mul_by_03(state[0][i]) ^ state[1][i] ^ state[2][i] ^ mul_by_02(state[3][i]) else: # decryption s0 = mul_by_0e(state[0][i]) ^ mul_by_0b(state[1][i]) ^ mul_by_0d(state[2][i]) ^ mul_by_09(state[3][i]) s1 = mul_by_09(state[0][i]) ^ mul_by_0e(state[1][i]) ^ mul_by_0b(state[2][i]) ^ mul_by_0d(state[3][i]) s2 = mul_by_0d(state[0][i]) ^ mul_by_09(state[1][i]) ^ mul_by_0e(state[2][i]) ^ mul_by_0b(state[3][i]) s3 = mul_by_0b(state[0][i]) ^ mul_by_0d(state[1][i]) ^ mul_by_09(state[2][i]) ^ mul_by_0e(state[3][i]) state[0][i] = s0 state[1][i] = s1 state[2][i] = s2 state[3][i] = s3 return state def key_expansion(key): """It makes list of RoundKeys for function AddRoundKey. All details about algorithm is is in AES standart """ #key_symbols = [ord(symbol) for symbol in key] key_symbols = key # ChipherKey shoul contain 16 symbols to fill 4*4 table. If it's less # complement the key with "0x01" if len(key_symbols) < 4 * nk: for i in range(4 * nk - len(key_symbols)): key_symbols.append(0x01) # make ChipherKey(which is base of KeySchedule) key_schedule = [[] for i in range(4)] for r in range(4): for c in range(nk): key_schedule[r].append(key_symbols[r + 4 * c]) # Comtinue to fill KeySchedule for col in range(nk, nb * (nr + 1)): # col - column number if col % nk == 0: # take shifted (col - 1)th column... tmp = [key_schedule[row][col - 1] for row in range(1, 4)] tmp.append(key_schedule[0][col - 1]) # change its elements using Sbox-table like in SubBytes... for j in range(len(tmp)): sbox_row = tmp[j] // 0x10 sbox_col = tmp[j] % 0x10 sbox_elem = sbox[16 * sbox_row + sbox_col] tmp[j] = sbox_elem # and finally make XOR of 3 columns for row in range(4): s = (key_schedule[row][col - 4]) ^ (tmp[row]) ^ (rcon[row][int(col / nk - 1)]) key_schedule[row].append(s) else: # just make XOR of 2 columns for row in range(4): s = key_schedule[row][col - 4] ^ key_schedule[row][col - 1] key_schedule[row].append(s) return key_schedule def add_round_key(state, key_schedule, round=0): """That transformation combines State and KeySchedule together. Xor of State and RoundSchedule(part of KeySchedule). """ for col in range(nk): # nb*round is a shift which indicates start of a part of the KeySchedule s0 = state[0][col] ^ key_schedule[0][nb * round + col] s1 = state[1][col] ^ key_schedule[1][nb * round + col] s2 = state[2][col] ^ key_schedule[2][nb * round + col] s3 = state[3][col] ^ key_schedule[3][nb * round + col] state[0][col] = s0 state[1][col] = s1 state[2][col] = s2 state[3][col] = s3 return state # Small helpful functions block def left_shift(array, count): """Rotate the array over count times""" res = array[:] for i in range(count): temp = res[1:] temp.append(res[0]) res[:] = temp[:] return res def right_shift(array, count): """Rotate the array over count times""" res = array[:] for i in range(count): tmp = res[:-1] tmp.insert(0, res[-1]) res[:] = tmp[:] return res def mul_by_02(num): """The function multiplies by 2 in Galua space""" if num < 0x80: res = (num << 1) else: res = (num << 1) ^ 0x1b return res % 0x100 def mul_by_03(num): """The function multiplies by 3 in Galua space example: 0x03*num = (0x02 + 0x01)num = num*0x02 + num Addition in Galua field is oparetion XOR """ return (mul_by_02(num) ^ num) def mul_by_09(num): # return mul_by_03(num)^mul_by_03(num)^mul_by_03(num) - works wrong, I don't know why return mul_by_02(mul_by_02(mul_by_02(num))) ^ num def mul_by_0b(num): # return mul_by_09(num)^mul_by_02(num) return mul_by_02(mul_by_02(mul_by_02(num))) ^ mul_by_02(num) ^ num def mul_by_0d(num): # return mul_by_0b(num)^mul_by_02(num) return mul_by_02(mul_by_02(mul_by_02(num))) ^ mul_by_02(mul_by_02(num)) ^ num def mul_by_0e(num): # return mul_by_0d(num)^num return mul_by_02(mul_by_02(mul_by_02(num))) ^ mul_by_02(mul_by_02(num)) ^ mul_by_02(num) # End of small helpful functions block