# AES implementation in Python

After implementing DES, the next obvious challenge was AES. I was expecting AES code to be simpler to write than DES’ because AES was designed to be implemented in hardware or software, while DES design was geared towards hardware. This time, however, I decided to write an object-oriented API supporting the three different key sizes AES inherited from Rijndael (128-, 192- and 256-bit). In addition, besides the ECB (Electronic Code Book) basic operation mode, this implementation also supports CBC (Cipher Block Chaining) mode.

```#!/usr/bin/python3
#
# Author: Joao H de A Franco (jhafranco@acm.org)
#
# Description: AES implementation in Python 3
# (sundAES)
#
# Date: 2013-06-02 (version 1.1)
#       2012-01-16 (version 1.0)
#
# (CC BY-NC-SA 3.0)
#===========================================================
import sys
from itertools import repeat
from functools import reduce
from copy import copy

__all__ = ["setKey","encrypt","decrypt"]

def memoize(func):
"""Memoization function"""
memo = {}
def helper(x):
if x not in memo:
memo[x] = func(x)
return memo[x]
return helper

def mult(p1,p2):
"""Multiply two polynomials in GF(2^8)/x^8+x^4+x^3+x+1"""
p = 0
while p2:
if p2&0x01:
p ^= p1
p1 <<= 1
if p1&0x100:
p1 ^= 0x1b
p2 >>= 1
return p&0xff

# Auxiliary one-parameter functions defined for memoization
# (to speed up multiplication in GF(2^8))

@memoize
def x2(y):
"""Multiplication by 2"""
return mult(2,y)

@memoize
def x3(y):
"""Multiplication by 3"""
return mult(3,y)

@memoize
def x9(y):
"""Multiplication by 9"""
return mult(9,y)

@memoize
def x11(y):
"""Multiplication by 11"""
return mult(11,y)

@memoize
def x13(y):
"""Multiplication by 13"""
return mult(13,y)

@memoize
def x14(y):
"""Multiplication by 14"""
return mult(14,y)

class AES:
"""Class definition for AES objects"""
keySizeTable = {"SIZE_128":16,
"SIZE_192":24,
"SIZE_256":32}
wordSizeTable = {"SIZE_128":44,
"SIZE_192":52,
"SIZE_256":60}
numberOfRoundsTable = {"SIZE_128":10,
"SIZE_192":12,
"SIZE_256":14}
cipherModeTable = {"MODE_ECB":1,
"MODE_CBC":2}
# S-Box
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,
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)
# Inverse S-Box
invSBox = (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,
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)

# Instance variables
wordSize = None
w = [None]*60 # Round subkeys list
keyDefined = None # Key definition flag
numberOfRounds = None
cipherMode = None
ivEncrypt = None # Initialization
ivDecrypt = None # vectors

"""Create a new instance of an AES object"""
try:
assert mode in AES.cipherModeTable
except AssertionError:
print("Cipher mode not supported:",mode)
sys.exit("ValueError")
self.cipherMode = mode
try:
except AssertionError:
sys.exit(ValueError)
self.keyDefined = False

def intToList(self,number):
"""Convert an 16-byte number into a 16-element list"""
return [(number>>i)&0xff for i in reversed(range(0,128,8))]

def intToList2(self,number):
"""Converts an integer into one (or more) 16-element list"""
lst = []
while number:
lst.append(number&0xff)
number >>= 8
m = len(lst)%16
if m == 0 and len(lst) != 0:
return lst[::-1]
else:
return list(bytes(16-m)) + lst[::-1]

def listToInt(self,lst):
"""Convert a list into a number"""
return reduce(lambda x,y:(x<<8)+y,lst)

def wordToState(self,wordList):
"""Convert list of 4 words into a 16-element state list"""
return [(wordList[i]>>j)&0xff
for j in reversed(range(0,32,8)) for i in range(4)]

def listToState(self,list):
"""Convert a 16-element list into a 16-element state list"""
return [list[i+j] for j in range(4) for i in range(0,16,4)]

stateToList = listToState # this function is an involution

def subBytes(self,state):
"""SubBytes transformation"""
return [AES.sBox[e] for e in state]

def invSubBytes(self,state):
"""Inverse SubBytes transformation"""
return [AES.invSBox[e] for e in state]

def shiftRows(self,s):
"""ShiftRows transformation"""
return s[:4]+s[5:8]+s[4:5]+s[10:12]+s[8:10]+s[15:]+s[12:15]

def invShiftRows(self,s):
"""Inverse ShiftRows transformation"""
return s[:4]+s[7:8]+s[4:7]+s[10:12]+s[8:10]+s[13:]+s[12:13]

def mixColumns(self,s):
"""MixColumns transformation"""
return [x2(s[i])^x3(s[i+4])^ s[i+8] ^ s[i+12] for i in range(4)]+ \
[ s[i] ^x2(s[i+4])^x3(s[i+8])^ s[i+12] for i in range(4)]+ \
[ s[i] ^ s[i+4] ^x2(s[i+8])^x3(s[i+12]) for i in range(4)]+ \
[x3(s[i])^ s[i+4] ^ s[i+8] ^x2(s[i+12]) for i in range(4)]

def invMixColumns(self,s):
"""Inverse MixColumns transformation"""
return [x14(s[i])^x11(s[i+4])^x13(s[i+8])^ x9(s[i+12]) for i in range(4)]+ \
[ x9(s[i])^x14(s[i+4])^x11(s[i+8])^x13(s[i+12]) for i in range(4)]+ \
[x13(s[i])^ x9(s[i+4])^x14(s[i+8])^x11(s[i+12]) for i in range(4)]+ \
[x11(s[i])^x13(s[i+4])^ x9(s[i+8])^x14(s[i+12]) for i in range(4)]

return [i^j for i,j in zip(subkey,state)]

def rotWord(self,number):
"""Rotate subkey left"""
return (((number&0xff000000)>>24) +
((number&0xff0000)<<8) +
((number&0xff00)<<8) +
((number&0xff)<<8))

def subWord(self,key):
"""Substitute subkeys bytes using S-box"""
return ((AES.sBox[(key>>24)&0xff]<<24) +
(AES.sBox[(key>>16)&0xff]<<16) +
(AES.sBox[(key>>8)&0xff]<<8) +
AES.sBox[key&0xff])

def setKey(self,keySize,key,iv = None):
"""KeyExpansion transformation"""
rcon = (0x00,0x01,0x02,0x04,0x08,0x10,0x20,0x40,0x80,0x1B,0x36)
try:
assert keySize in AES.keySizeTable
except AssertionError:
print("Key size identifier not valid")
sys.exit("ValueError")
try:
assert isinstance(key,int)
except AssertionError:
print("Invalid key")
sys.exit("ValueError")
klen = len("{:02x}".format(key))//2
try:
assert klen <= AES.keySizeTable[keySize]
except AssertionError:
print("Key size mismatch")
sys.exit("ValueError")
try:
assert ((self.cipherMode == "MODE_CBC" and isinstance(iv,int)) or
self.cipherMode == "MODE_ECB")
except AssertionError:
print("IV is mandatory for CBC mode")
sys.exit(ValueError)

if self.cipherMode == "MODE_CBC":
temp = self.intToList(iv)
self.ivEncrypt = copy(temp)
self.ivDecrypt = copy(temp)
nr = AES.numberOfRoundsTable[keySize]
self.numberOfRounds = nr
self.wordSize = AES.wordSizeTable[keySize]
if nr == 10:
nk = 4
keyList = self.intToList(key)
elif nr == 12:
nk = 6
keyList = self.intToList(key>>64) + \
(self.intToList(key&int("ff"*32,16)))[8:]
else:
nk = 8
keyList = self.intToList(key>>128) + \
self.intToList(key&int("ff"*64,16))
for index in range(nk):
self.w[index] = (keyList[4*index]<<24) + \
(keyList[4*index+1]<<16) + \
(keyList[4*index+2]<<8) +\
keyList[4*index+3]
for index in range(nk,self.wordSize):
temp = self.w[index - 1]
if index % nk == 0:
temp = (self.subWord(self.rotWord(temp)) ^
rcon[index//nk]<<24)
elif self.numberOfRounds == 14 and index%nk == 4:
temp = self.subWord(temp)
self.w[index] = self.w[index-nk]^temp
self.keyDefined = True
return

def getKey(self,operation):
"""Return next round subkey for encryption or decryption"""
if operation == "encryption":
for i in range(0,self.wordSize,4):
yield self.wordToState(self.w[i:i+4])
else: # operation = "decryption":
for i in reversed(range(0,self.wordSize,4)):
yield self.wordToState(self.w[i:i+4])

def encryptBlock(self,plaintextBlock):
"""Encrypt a 16-byte block with key already defined"""
key = self.getKey("encryption")
state = self.listToState(plaintextBlock)
for _ in repeat(None,self.numberOfRounds - 1):
state = self.subBytes(state)
state = self.shiftRows(state)
state = self.mixColumns(state)
state = self.subBytes(state)
state = self.shiftRows(state)
return self.stateToList(state)

def decryptBlock(self,ciphertextBlock):
"""Decrypt a 16-byte block with key already defined"""
key = self.getKey("decryption")
state = self.listToState(ciphertextBlock)
for _ in repeat(None,self.numberOfRounds - 1):
state = self.invShiftRows(state)
state = self.invSubBytes(state)
state = self.invMixColumns(state)
state = self.invShiftRows(state)
state = self.invSubBytes(state)
return self.stateToList(state)

if type(data) is bytes:
else:

"""Remove PKCS7 padding (if present) from plaintext"""
return "".join(chr(e) for e in byteList[:-byteList[-1]])
else:
return "".join(chr(e) for e in byteList)

def encrypt(self,input):
"""Encrypt plaintext passed as a string or as an integer"""
try:
assert self.keyDefined
except AssertionError:
print("Key not defined")
sys.exit("ValueError")

if type(input) is int:
inList = self.intToList2(input)
else:
outList = []
if self.cipherMode == "MODE_CBC":
outBlock = self.ivEncrypt
for i in range(0,len(inList),16):
auxList = self.xorLists(outBlock,inList[i:i+16])
outBlock = self.encryptBlock(auxList)
outList += outBlock
self.ivEncrypt = outBlock
else:
for i in range(0,len(inList),16):
outList += self.encryptBlock(inList[i:i+16])
if type(input) is int:
return self.listToInt(outList)
else:
return outList

def decrypt(self,input):
"""Decrypt ciphertext passed as a string or as an integer"""
try:
assert self.keyDefined
except AssertionError:
print("Key not defined")
sys.exit("ValueError")
if type(input) is int:
inList = self.intToList2(input)
else:
inList = input
outList = []
if self.cipherMode == "MODE_CBC":
oldInBlock = self.ivDecrypt
for i in range(0,len(inList),16):
newInBlock = inList[i:i+16]
auxList = self.decryptBlock(newInBlock)
outList += self.xorLists(oldInBlock,auxList)
oldInBlock = newInBlock
self.ivDecrypt = oldInBlock
else:
for i in range(0,len(inList),16):
outList += self.decryptBlock(inList[i:i+16])
if type(input) is int:
return self.listToInt(outList)
else:
```

The code below informally verify the correctness of the implementation with the help of the test vectors described in NIST document SP800-38A, Recommendation for Block Cipher Modes of Operation – Methods and Techniques:

```import pyAES

def intToList(number):
"""Convert a 16-byte number into a 16-element list"""
return [(number >> 120) & 0xff, (number >> 112) & 0xff,
(number >> 104) & 0xff, (number >> 96)  & 0xff,
(number >> 88)  & 0xff, (number >> 80)  & 0xff,
(number >> 72)  & 0xff, (number >> 64)  & 0xff,
(number >> 56)  & 0xff, (number >> 48)  & 0xff,
(number >> 40)  & 0xff, (number >> 32)  & 0xff,
(number >> 24)  & 0xff, (number >> 16)  & 0xff,
(number >> 8)   & 0xff,  number & 0xff]

def intToText(hexNumber):
"""Convert a 16-byte number into a 16 char text string"""
return "".join(chr(e) for e in intToList(hexNumber))

def checkTestVector1(mode, keySize, key, plaintext, ciphertext, iv = None):
"""Check test vectors for single block encryption and decryption"""
success = True
obj = pyAES.AES(mode)
obj.setKey(keySize, key, iv)
for i, (p, c) in enumerate(zip(plaintext, ciphertext)):
p_text = intToText(p)
c_text = intToList(c)
code = "{0:3s}-{1:3s}".format(mode[5:], keySize[5:])
try:
assert obj.encrypt(p_text) == c_text
except AssertionError:
print(code, "encryption #{:d} failed".format(i))
success = False
try:
assert obj.decrypt(c_text) == p_text
except AssertionError:
print(code, "decryption #{:d} failed".format(i))
success = False
if success:
print(code, "encryption/decryption ok")
return success

def checkTestVector2(mode, keySize, plaintext, key1, key2, iv1 = None, iv2 = None):
obj1.setKey(keySize, key1, iv1)
obj2.setKey(keySize, key2, iv2)
ciphertext1 = obj1.encrypt(plaintext)
ciphertext2 = obj2.encrypt(plaintext)
plaintext1 = obj1.decrypt(ciphertext1)
plaintext2 = obj2.decrypt(ciphertext2)
code = "{0:3s}-{1:3s}".format(mode[5:], keySize[5:])
try:
assert plaintext1 == plaintext and plaintext2 == plaintext
except AssertionError:
print("Multi-block", code, "encryption/decryption failed")
return False
print("Multi-block", code, "encryption/decryption ok")
return True

#===========================================================================

# Test vectors from NIST SP800-38A sections F.1.1 and F.1.2
key = 0x2b7e151628aed2a6abf7158809cf4f3c
plaintext =  [0x6bc1bee22e409f96e93d7e117393172a,
0xae2d8a571e03ac9c9eb76fac45af8e51,
0x30c81c46a35ce411e5fbc1191a0a52ef,
0xf5d3d58503b9699de785895a96fdbaaf,
0x43b1cd7f598ece23881b00e3ed030688,
return checkTestVector1("MODE_ECB", "SIZE_128", key, plaintext, ciphertext)

# Test vectors from NIST SP800-38A sections F.1.3 and F.1.4
plaintext =  [0x6bc1bee22e409f96e93d7e117393172a,
0xae2d8a571e03ac9c9eb76fac45af8e51,
0x30c81c46a35ce411e5fbc1191a0a52ef,
ciphertext = [0xbd334f1d6e45f25ff712a214571fa5cc,
0x9a4b41ba738d6c72fb16691603c18e0e]
return checkTestVector1("MODE_ECB", "SIZE_192", key, plaintext, ciphertext)

# Test vectors from NIST SP800-38A sections F.1.5 and F.1.6
key = 0x603deb1015ca71be2b73aef0857d77811f352c073b6108d72d9810a30914dff4
plaintext =  [0x6bc1bee22e409f96e93d7e117393172a,
0xae2d8a571e03ac9c9eb76fac45af8e51,
0x30c81c46a35ce411e5fbc1191a0a52ef,
ciphertext = [0xf3eed1bdb5d2a03c064b5a7e3db181f8,
0x591ccb10d410ed26dc5ba74a31362870,
0xb6ed21b99ca6f4f9f153e7b1beafed1d,
0x23304b7a39f9f3ff067d8d8f9e24ecc7]
return checkTestVector1("MODE_ECB", "SIZE_256", key, plaintext, ciphertext)

# Test vectors from NIST SP800-38A sections F.2.1 and F.2.2
key = 0x2b7e151628aed2a6abf7158809cf4f3c
iv = 0x000102030405060708090a0b0c0d0e0f
plaintext =  [0x6bc1bee22e409f96e93d7e117393172a,
0xae2d8a571e03ac9c9eb76fac45af8e51,
0x30c81c46a35ce411e5fbc1191a0a52ef,
ciphertext = [0x7649abac8119b246cee98e9b12e9197d,
0x5086cb9b507219ee95db113a917678b2,
0x73bed6b8e3c1743b7116e69e22229516,
0x3ff1caa1681fac09120eca307586e1a7]
return checkTestVector1("MODE_CBC", "SIZE_128", key, plaintext, ciphertext, iv)

# Test vectors from NIST SP800-38A sections F.2.3 and F.2.4
iv = 0x000102030405060708090a0b0c0d0e0f
plaintext =  [0x6bc1bee22e409f96e93d7e117393172a,
0xae2d8a571e03ac9c9eb76fac45af8e51,
0x30c81c46a35ce411e5fbc1191a0a52ef,
ciphertext = [0x4f021db243bc633d7178183a9fa071e8,
0x571b242012fb7ae07fa9baac3df102e0,
0x08b0e27988598881d920a9e64f5615cd]
return checkTestVector1("MODE_CBC", "SIZE_192", key, plaintext, ciphertext, iv)

# Test vectors from NIST SP800-38A sections F.2.5 and F.2.6
key = 0x603deb1015ca71be2b73aef0857d77811f352c073b6108d72d9810a30914dff4
iv = 0x000102030405060708090a0b0c0d0e0f
plaintext=  [0x6bc1bee22e409f96e93d7e117393172a,
0xae2d8a571e03ac9c9eb76fac45af8e51,
0x30c81c46a35ce411e5fbc1191a0a52ef,
ciphertext = [0xf58c4c04d6e5f1ba779eabfb5f7bfbd6,
0x9cfc4e967edb808d679f777bc6702c7d,
0x39f23369a9d9bacfa530e26304231461,
0xb2eb05e2c39be9fcda6c19078c6a9d1b]
return checkTestVector1("MODE_CBC", "SIZE_256", key, plaintext, ciphertext, iv)

#===========================================================================

# Two multi-block encryptions in ECB mode with 128-bit key
def ECB_128_PKCS5():
plaintext = "The quick brown fox jumps over the lazy dog"
key1 = 0x000102030405060708090a0b0c0d0e0f
key2 = 0xffeeddccbbaa99887766554433221100
return checkTestVector2("MODE_ECB", "SIZE_128", plaintext, key1, key2)

# Two multi-block encryptions in ECB mode with 192-bit key
def ECB_192_PKCS5():
plaintext = "The quick brown fox jumps over the lazy dog"
key1 = 0x000102030405060708090a0b0c0d0e0f1011121314151617
key2 = 0x1716151413121110ffeeddccbbaa99887766554433221100
return checkTestVector2("MODE_ECB", "SIZE_192", plaintext, key1, key2)

# Two multi-block encryptions in ECB mode with 256-bit key
def ECB_256_PKCS5():
plaintext = "The quick brown fox jumps over the lazy dog"
key1 = 0x000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f
key2 = 0x1f1e1d1c1b1a19181716151413121110ffeeddccbbaa99887766554433221100
return checkTestVector2("MODE_ECB", "SIZE_256", plaintext, key1, key2)

# Two multi-block encryptions in CBC mode with 128-bit key
def CBC_128_PKCS5():
plaintext = "The quick brown fox jumps over the lazy dog"
key1 = 0x000102030405060708090a0b0c0d0e0f
key2 = 0xffeeddccbbaa99887766554433221100
iv1 = 0x0123cdef456789ab0123cdef456789ab
iv2 = 0xab0123cdef456789ab0123cdef456789
return checkTestVector2("MODE_CBC", "SIZE_128", plaintext, key1, key2, iv1, iv2)

# Two multi-block encryptions in CBC mode with 192-bit key
def CBC_192_PKCS5():
plaintext = "The quick brown fox jumps over the lazy dog"
key1 = 0x000102030405060708090a0b0c0d0e0f1011121314151617
key2 = 0x1716151413121110ffeeddccbbaa99887766554433221100
iv1 = 0x0123cdef456789ab0123cdef456789ab
iv2 = 0xab0123cdef456789ab0123cdef456789
return checkTestVector2("MODE_CBC", "SIZE_192", plaintext, key1, key2, iv1, iv2)

# Two multi-block encryptions in CBC mode with 256-bit key
def CBC_256_PKCS5():
plaintext = "The quick brown fox jumps over the lazy dog"
key1 = 0x000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f
key2 = 0x1f1e1d1c1b1a19181716151413121110ffeeddccbbaa99887766554433221100
iv1 = 0x0123cdef456789ab0123cdef456789ab
iv2 = 0xab0123cdef456789ab0123cdef456789
return checkTestVector2("MODE_CBC", "SIZE_256", plaintext, key1, key2, iv1, iv2)

def main():
# Perform vector tests
testSuccess = True
for mode in ["ECB", "CBC"]:
for size in ["128", "192", "256"]:
testVector = mode + "_" + size + "_" + pad + "()"
testSuccess = testSuccess & eval(testVector)
if testSuccess:
print("All tests passed!")

if __name__ == '__main__':
main()
```

## 7 thoughts on “AES implementation in Python”

1. This is really interesting, You are a very skilled blogger.

I’ve joined your feed and look forward to seeking more of your fantastic post. Also, I’ve shared your website in my social
networks!

2. This looks really nice, together with your GCM implementation. One question, though: in *padData*, my python3 doesn’t like “[ord(s) for s in string]”; it seems to prefer return [s for s in string]. string is of class bytes, I think, and s in returns the integer already.

I’m not absolutely sure of this; I’ve had great difficulty in absorbing the changes in string handling from py2 to py3, so please forgive me if I’ve got this wrong.

• Hello Brent,

In fact, when you iterate over a string you’ll get all its elements, one by one, which are also of type string. You can check this by evaluating the expression [s for s in “abc”], which returns the list [‘a’,’b’,’c’]. If a list of integers is needed, the expression [ord(s) for s in “abc”] does the job, since it evaluates to [97,98,99]. There is no difference in this behavior in Python 2 and Python 3.

Regards,

JH

3. Hi
I would like to ask a question on mixColumns function. In the text book, I notice that the computation of function is based on the input indexes of columns as [0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11], [12, 13, 14, 15]. Where as in your implementation, the indexes are [0, 4, 8, 12], [1, 5, 9, 13], [2, 6, 10, 14], [3, 7, 11, 15]. Certainly, the encryption and decryption would work without error for both cases if the inverse functions are implemented with same indexes. However, these two options of implementation are not able to inter-work, meaning one encryption work with the other decryption.
I am using “Understanding Cryptography” book. I may interpret the text wrongly. Do you have other specification in this mixColumns function to share?
I have read the implement of slowAES program, which is using the second option.
Hope you could help my understand.

Thanks

CHUA Chew Bock