pykms_Aes.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

# aes.py: implements AES - Advanced Encryption Standard
# from the SlowAES project, http://code.google.com/p/slowaes/
#
# Copyright (c) 2008    Josh Davis ( http://www.josh-davis.org )
#                       Alex Martelli ( http://www.aleax.it )
#
# Modified for py-kms, Python 2 / 3 compatible 
# Copyright (c) 2019    Matteo Fan  ( SystemRage@protonmail.com )
#
# Ported from C code written by Laurent Haan ( http://www.progressive-coding.com )

# Licensed under the Apache License, Version 2.0
# http://www.apache.org/licenses/
#

from __future__ import print_function, unicode_literals
import os
import math

def append_PKCS7_padding(val):
    """ Function to pad the given data to a multiple of 16-bytes by PKCS7 padding. """
    numpads = 16 - (len(val) % 16)
    return val + numpads * bytearray(chr(numpads).encode('utf-8'))

def strip_PKCS7_padding(val):
    """ Function to strip off PKCS7 padding. """
    
    if len(val) % 16 or not val:
        raise ValueError("String of len %d can't be PCKS7-padded" % len(val))
    numpads = val[-1]
    if numpads > 16:
        raise ValueError("String ending with %r can't be PCKS7-padded" % val[-1])
    return val[:-numpads]


class AES( object ):
    """ Class implementing the Advanced Encryption Standard algorithm. """
    
    #*py-kms*
    v6 = False

    # Valid key sizes
    KeySize = {
                "SIZE_128": 16,
                "SIZE_192": 24,
                "SIZE_256": 32
                }

    # Rijndael 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, 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 ]

    # Rijndael Inverted S-box
    rsbox = [ 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 ]

    # Rijndael Rcon
    Rcon = [ 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36,
             0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97,
             0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72,
             0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66,
             0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04,
             0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d,
             0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3,
             0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61,
             0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a,
             0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40,
             0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc,
             0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5,
             0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a,
             0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d,
             0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c,
             0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35,
             0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4,
             0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc,
             0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08,
             0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a,
             0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d,
             0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2,
             0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74,
             0xe8, 0xcb ]

    def getSBoxValue(self,num):
        """ Method to retrieve a given S-Box value. """
        return self.sbox[num]

    def getSBoxInvert(self,num):
        """ Method to retrieve a given Inverted S-Box value."""
        return self.rsbox[num]

    def rotate(self, word):
        """ Method performing Rijndael's key schedule rotate operation.
            Rotate a word eight bits to the left: eg, rotate(1d2c3a4f) == 2c3a4f1d
            @param word: char list of size 4 (32 bits overall).
        """
        return word[1:] + word[:1]

    def getRconValue(self, num):
        """ Method to retrieve a given Rcon value. """
        return self.Rcon[num]

    def core(self, word, iteration):
        """ Method performing the key schedule core operation. """
        # Rotate the 32-bit word 8 bits to the left.
        word = self.rotate(word)
        # Apply S-Box substitution on all 4 parts of the 32-bit word.
        for i in range(4):
            word[i] = self.getSBoxValue(word[i])
        # XOR the output of the rcon operation with i to the first part (leftmost) only.
        word[0] = word[0] ^ self.getRconValue(iteration)
        return word

    def expandKey(self, key, size, expandedKeySize):
        """ Method performing Rijndael's key expansion.
            Expands an 128, 192, 256 key into an 176, 208, 240 bytes key.
        """
        # Current expanded keySize, in bytes.
        currentSize = 0
        rconIteration = 1
        expandedKey = [0] * expandedKeySize

        # Set the 16, 24, 32 bytes of the expanded key to the input key.
        for j in range(size):
            expandedKey[j] = key[j]
        currentSize += size

        while currentSize < expandedKeySize:
            # Assign the previous 4 bytes to the temporary value t.
            t = expandedKey[currentSize - 4:currentSize]

            # Every 16,24,32 bytes we apply the core schedule to t
            # and increment rconIteration afterwards.
            if currentSize % size == 0:
                t = self.core(t, rconIteration)
                rconIteration += 1
            # For 256-bit keys, we add an extra sbox to the calculation.
            if size == self.KeySize["SIZE_256"] and ((currentSize % size) == 16):
                for l in range(4):
                    t[l] = self.getSBoxValue(t[l])

            # We XOR t with the four-byte block 16,24,32 bytes before the new
            # expanded key. This becomes the next four bytes in the expanded key.
            for m in range(4):
                expandedKey[currentSize] = expandedKey[currentSize - size] ^ t[m]
                currentSize += 1
        return expandedKey

    def addRoundKey(self, state, roundKey):
        """ Method to add (XORs) the round key to the state. """
        for i in range(16):
            state[i] ^= roundKey[i]
        return state

    def createRoundKey(self, expandedKey, roundKeyPointer):
        """ Creates a round key from the given expanded key and the
            position within the expanded key.
        """
        roundKey = [0] * 16
        for i in range(4):
            for j in range(4):
                roundKey[j * 4 + i] = expandedKey[roundKeyPointer + i * 4 + j]
        return roundKey

    def galois_multiplication(self, a, b):
        """ Method to perform a Galois multiplication of 8 bit characters
            a and b.
        """
        p = 0
        for counter in range(8):
            if b & 1:
                p ^= a
            hi_bit_set = a & 0x80
            a <<= 1
            # keep a 8 bit
            a &= 0xFF
            if hi_bit_set:
                a ^= 0x1b
            b >>= 1
        return p

    def subBytes(self, state, isInv):
        """ Method to substitute all the values from the state with the
            value in the SBox using the state value as index for the SBox.
        """
        if isInv:
            getter = self.getSBoxInvert
        else:
            getter = self.getSBoxValue
        for i in range(16):
            state[i] = getter(state[i])
        return state

    def shiftRows(self, state, isInv):
        """ Method to iterate over the 4 rows and call shiftRow(...) with that row. """
        for i in range(4):
            state = self.shiftRow(state, i * 4, i, isInv)
        return state

    def shiftRow(self, state, statePointer, nbr, isInv):
        """ Method to shift the row to the left. """
        for i in range(nbr):
            if isInv:
                state[statePointer:statePointer + 4] = state[statePointer + 3:statePointer + 4] + \
                                                       state[statePointer:statePointer + 3]
            else:
                state[statePointer:statePointer + 4] = state[statePointer + 1:statePointer + 4] + \
                                                       state[statePointer:statePointer + 1]
        return state


    def mixColumns(self, state, isInv):
        """ Method to perform a galois multiplication of the 4x4 matrix. """
        # Iterate over the 4 columns.
        for i in range(4):
            # Construct one column by slicing over the 4 rows.
            column = state[i:i + 16:4]
            # Apply the mixColumn on one column.
            column = self.mixColumn(column, isInv)
            # Put the values back into the state.
            state[i:i + 16:4] = column
        return state

    def mixColumn(self, column, isInv):
        """ Method to perform a galois multiplication of 1 column the 4x4 matrix. """
        if isInv:
            mult = [14, 9, 13, 11]
        else:
            mult = [2, 1, 1, 3]
        cpy = list(column)
        g = self.galois_multiplication

        column[0] = g(cpy[0], mult[0]) ^ g(cpy[3], mult[1]) ^ \
                    g(cpy[2], mult[2]) ^ g(cpy[1], mult[3])
        column[1] = g(cpy[1], mult[0]) ^ g(cpy[0], mult[1]) ^ \
                    g(cpy[3], mult[2]) ^ g(cpy[2], mult[3])
        column[2] = g(cpy[2], mult[0]) ^ g(cpy[1], mult[1]) ^ \
                    g(cpy[0], mult[2]) ^ g(cpy[3], mult[3])
        column[3] = g(cpy[3], mult[0]) ^ g(cpy[2], mult[1]) ^ \
                    g(cpy[1], mult[2]) ^ g(cpy[0], mult[3])
        return column


    def aes_round(self, state, roundKey, roundKms):
        """ Method to apply the 4 operations of the forward round in sequence. """
        state = self.subBytes(state, False)
        state = self.shiftRows(state, False)
        state = self.mixColumns(state, False)

        #*py-kms*
        if self.v6:
          if roundKms == 4:
            state[0] ^= 0x73
          if roundKms == 6:
            state[0] ^= 0x09
          if roundKms == 8:
            state[0] ^= 0xE4
            
        state = self.addRoundKey(state, roundKey)
        return state

    def aes_invRound(self, state, roundKey, roundKms):
        """ Method to apply the 4 operations of the inverse round in sequence. """
        state = self.shiftRows(state, True)
        state = self.subBytes(state, True)
        state = self.addRoundKey(state, roundKey)

        #*py-kms*
        if self.v6:
          if roundKms == 4:
            state[0] ^= 0x73
          if roundKms == 6:
            state[0] ^= 0x09
          if roundKms == 8:
            state[0] ^= 0xE4

        state = self.mixColumns(state, True)
        return state


    def aes_main(self, state, expandedKey, nbrRounds):
        """ Method to do the AES encryption for one round.
        
            Perform the initial operations, the standard round and the
            final operations of the forward AES, creating a round key for each round.
        """
        state = self.addRoundKey(state, self.createRoundKey(expandedKey, 0))
        i = 1
        while i < nbrRounds:
            state = self.aes_round(state, self.createRoundKey(expandedKey, 16 * i), i)
            i += 1
        state = self.subBytes(state, False)
        state = self.shiftRows(state, False)
        state = self.addRoundKey(state, self.createRoundKey(expandedKey, 16 * nbrRounds))
        return state


    def aes_invMain(self, state, expandedKey, nbrRounds):
        """ Method to do the inverse AES encryption for one round.
        
            Perform the initial operations, the standard round, and the
            final operations of the inverse AES, creating a round key for each round.
        """
        state = self.addRoundKey(state, self.createRoundKey(expandedKey, 16 * nbrRounds))
        i = nbrRounds - 1
        while i > 0:
            state = self.aes_invRound(state, self.createRoundKey(expandedKey, 16 * i), i)
            i -= 1
        state = self.shiftRows(state, True)
        state = self.subBytes(state, True)
        state = self.addRoundKey(state, self.createRoundKey(expandedKey, 0))
        return state

    def encrypt(self, iput, key, size):
        """ Method to encrypt a 128 bit input block against the given key
            of size specified.
        """
        output = [0] * 16
        # The number of rounds.
        nbrRounds = 0
        # The 128 bit block to encode.
        block = [0] * 16
        # Set the number of rounds.
        if size == self.KeySize["SIZE_128"]:
            nbrRounds = 10
        elif size == self.KeySize["SIZE_192"]:
            nbrRounds = 12
        elif size == self.KeySize["SIZE_256"]:
            nbrRounds = 14
        # *py-kms* The KMS v4 parameters.
        elif size == 20:
            nbrRounds = 11
        else:
            raise ValueError("Wrong key size given ({}).".format(size))

        # The expanded keySize.
        expandedKeySize = 16 * (nbrRounds + 1)

        # Set the block values, for the block:
        # a[0,0] a[0,1] a[0,2] a[0,3]
        # a[1,0] a[1,1] a[1,2] a[1,3]
        # a[2,0] a[2,1] a[2,2] a[2,3]
        # a[3,0] a[3,1] a[3,2] a[3,3]
        # the mapping order is a[0,0] a[1,0] a[2,0] a[3,0] a[0,1] a[1,1] ... a[2,3] a[3,3]
       
        # Iterate over the columns and over the rows.
        for i in range(4):
            for j in range(4):
                block[i + j * 4] = iput[i * 4 +j]

        # Expand the key into an 176, 208, 240 bytes key
        expandedKey = self.expandKey(key, size, expandedKeySize)

        # Encrypt the block using the expandedKey.
        block = self.aes_main(block, expandedKey, nbrRounds)

        # Unmap the block again into the output.
        for k in range(4):
            for l in range(4):
                output[k * 4 + l] = block[k + l * 4]
        return output


    def decrypt(self, iput, key, size):
        """ Method to decrypt a 128 bit input block against the given key
            of size specified.
        """
        output = [0] * 16
        # The number of rounds.
        nbrRounds = 0
        # The 128 bit block to decode.
        block = [0] * 16
        # Set the number of rounds.
        if size == self.KeySize["SIZE_128"]:
            nbrRounds = 10
        elif size == self.KeySize["SIZE_192"]:
            nbrRounds = 12
        elif size == self.KeySize["SIZE_256"]:
            nbrRounds = 14
        #*py-kms* The KMS v4 parameters.
        elif size == 20:
            nbrRounds = 11
        else:
            raise ValueError("Wrong key size given ({}).".format(size))

        # The expanded keySize.
        expandedKeySize = 16 * (nbrRounds + 1)

        # Set the block values, for the block:
        # a[0,0] a[0,1] a[0,2] a[0,3]
        # a[1,0] a[1,1] a[1,2] a[1,3]
        # a[2,0] a[2,1] a[2,2] a[2,3]
        # a[3,0] a[3,1] a[3,2] a[3,3]
        # the mapping order is a[0,0] a[1,0] a[2,0] a[3,0] a[0,1] a[1,1] ... a[2,3] a[3,3]

        # Iterate over the columns and the rows.
        for i in range(4):
            for j in range(4):
                block[i + j * 4] = iput[i * 4 + j]
                
        # Expand the key into an 176, 208, 240 bytes key.
        expandedKey = self.expandKey(key, size, expandedKeySize)
        # Decrypt the block using the expandedKey.
        block = self.aes_invMain(block, expandedKey, nbrRounds)
        # Unmap the block again into the output.
        for k in range(4):
            for l in range(4):
                output[k * 4 +l] = block[k + l * 4]
        return output


class AESModeOfOperation( object ):
    """ Class implementing the different AES mode of operations. """
  
    aes = AES()

    # Supported modes of operation.
    ModeOfOperation = {
                        "OFB": 0,
                        "CFB": 1,
                        "CBC": 2
                        }

    def convertString(self, string, start, end, mode):
        """ Method to convert a 16 character string into a number array. """
        if end - start > 16:
            end = start + 16
        if mode == self.ModeOfOperation["CBC"]:
            ar = [0] * 16
        else:
            ar = []

        i = start
        j = 0
        while len(ar) < end - start:
            ar.append(0)
        while i < end:
            ar[j] = string[i]
            j += 1
            i += 1
        return ar


    def encrypt(self, stringIn, mode, key, size, IV):
        """ Method to perform the encryption operation.
        
            @param stringIn: input string to be encrypted
            @param mode: mode of operation (0, 1 or 2)
            @param key: a hex key of the bit length size
            @param size: the bit length of the key (16, 24 or 32)
            @param IV: the 128 bit hex initilization vector
            @return tuple with mode of operation, length of the input and the encrypted data
        """
        if len(key) % size:
            raise ValueError("Illegal size ({}) for key '{}'.".format(size, key))
        if len(IV) % 16:
            raise ValueError("IV is not a multiple of 16.")
        # The AES input/output.
        plaintext = []
        iput = [0] * 16
        output = []
        ciphertext = [0] * 16
        # The output cipher string.
        cipherOut = []
        
        firstRound = True
        if stringIn != None:
            for j in range(int(math.ceil(float(len(stringIn))/16))):
                start = j * 16
                end = j * 16 + 16
                if end > len(stringIn):
                    end = len(stringIn)
                plaintext = self.convertString(stringIn, start, end, mode)
                
                if mode == self.ModeOfOperation["CFB"]:
                    if firstRound:
                        output = self.aes.encrypt(IV, key, size)
                        firstRound = False
                    else:
                        output = self.aes.encrypt(iput, key, size)
                    for i in range(16):
                        if len(plaintext) - 1 < i:
                            ciphertext[i] = 0 ^ output[i]
                        elif len(output) - 1 < i:
                            ciphertext[i] = plaintext[i] ^ 0
                        elif len(plaintext) - 1 < i and len(output) < i:
                            ciphertext[i] = 0 ^ 0
                        else:
                            ciphertext[i] = plaintext[i] ^ output[i]
                    for k in range(end - start):
                        cipherOut.append(ciphertext[k])
                    iput = ciphertext
                    
                elif mode == self.ModeOfOperation["OFB"]:
                    if firstRound:
                        output = self.aes.encrypt(IV, key, size)
                        firstRound = False
                    else:
                        output = self.aes.encrypt(iput, key, size)
                    for i in range(16):
                        if len(plaintext) - 1 < i:
                            ciphertext[i] = 0 ^ output[i]
                        elif len(output) - 1 < i:
                            ciphertext[i] = plaintext[i] ^ 0
                        elif len(plaintext) - 1 < i and len(output) < i:
                            ciphertext[i] = 0 ^ 0
                        else:
                            ciphertext[i] = plaintext[i] ^ output[i]
                    for k in range(end - start):
                        cipherOut.append(ciphertext[k])
                    iput = output
                    
                elif mode == self.ModeOfOperation["CBC"]:
                    for i in range(16):
                        if firstRound:
                            iput[i] =  plaintext[i] ^ IV[i]
                        else:
                            iput[i] =  plaintext[i] ^ ciphertext[i]
                    firstRound = False
                    ciphertext = self.aes.encrypt(iput, key, size)
                    # Always 16 bytes because of the padding for CBC.
                    for k in range(16):
                        cipherOut.append(ciphertext[k])
        return mode, len(stringIn), cipherOut


    def decrypt(self, cipherIn, originalsize, mode, key, size, IV):
        """ Method to perform the decryption operation.
        
            @param cipherIn: encrypted string to be decrypted
            @param originalsize: unencrypted string length (required for CBC)
            @param mode: mode of operation (0, 1 or 2)
            @param key: a number array of the bit length size
            @param size: the bit length of the key (16, 24 or 32)
            @param IV: the 128 bit number array initilization vector
            @return decrypted data 
        """
        if len(key) % size:
            raise ValueError("Illegal size ({}) for key '{}'.".format(size, key))
        if len(IV) % 16:
            raise ValueError("IV is not a multiple of 16.")
        # The AES input/output.
        ciphertext = []
        iput = []
        output = []
        plaintext = [0] * 16
        # The output plain text character list.
        chrOut = []
        
        firstRound = True
        if cipherIn != None:
            for j in range(int(math.ceil(float(len(cipherIn))/16))):
                start = j * 16
                end = j * 16 + 16
                if end > len(cipherIn):
                    end = len(cipherIn)
                ciphertext = cipherIn[start:end]
                
                if mode == self.ModeOfOperation["CFB"]:
                    if firstRound:
                        output = self.aes.encrypt(IV, key, size)
                        firstRound = False
                    else:
                        output = self.aes.encrypt(iput, key, size)
                    for i in range(16):
                        if len(output) - 1 < i:
                            plaintext[i] = 0 ^ ciphertext[i]
                        elif len(ciphertext) - 1 < i:
                            plaintext[i] = output[i] ^ 0
                        elif len(output) - 1 < i and len(ciphertext) < i:
                            plaintext[i] = 0 ^ 0
                        else:
                            plaintext[i] = output[i] ^ ciphertext[i]
                    for k in range(end - start):
                        chrOut.append(plaintext[k])
                    iput = ciphertext
                    
                elif mode == self.ModeOfOperation["OFB"]:
                    if firstRound:
                        output = self.aes.encrypt(IV, key, size)
                        firstRound = False
                    else:
                        output = self.aes.encrypt(iput, key, size)
                    for i in range(16):
                        if len(output) - 1 < i:
                            plaintext[i] = 0 ^ ciphertext[i]
                        elif len(ciphertext) - 1 < i:
                            plaintext[i] = output[i] ^ 0
                        elif len(output) - 1 < i and len(ciphertext) < i:
                            plaintext[i] = 0 ^ 0
                        else:
                            plaintext[i] = output[i] ^ ciphertext[i]
                    for k in range(end - start):
                        chrOut.append(plaintext[k])
                    iput = output
                    
                elif mode == self.ModeOfOperation["CBC"]:
                    output = self.aes.decrypt(ciphertext, key, size)
                    for i in range(16):
                        if firstRound:
                            plaintext[i] = IV[i] ^ output[i]
                        else:
                            plaintext[i] = iput[i] ^ output[i]
                    firstRound = False
                    if originalsize is not None and originalsize < end:
                        for k in range(originalsize - start):
                            chrOut.append(plaintext[k])
                    else:
                        for k in range(end - start):
                            chrOut.append(plaintext[k])
                    iput = ciphertext
        return chrOut


def encryptData(key, data, mode=AESModeOfOperation.ModeOfOperation["CBC"]):
    """ Module function to encrypt the given data with the given key.
    
        @param key: key to be used for encryption
        @param data: data to be encrypted 
        @param mode: mode of operations (0, 1 or 2)
        @return encrypted data prepended with the initialization vector
    """
    if mode == AESModeOfOperation.ModeOfOperation["CBC"]:
        data = append_PKCS7_padding(data)

    keysize = len(key) 
    assert keysize in AES.KeySize.values(), 'invalid key size: {}'.format(keysize)
    # Create a new iv using random data.
    iv = bytearray(os.urandom(16))
    moo = AESModeOfOperation()
    (mode, length, ciph) = moo.encrypt(data, mode, key, keysize, iv)
    # With padding, the original length does not need to be known.
    # It's a bad idea to store the original message length prepend the iv.
    return iv + bytearray(ciph)

def decryptData(key, data, mode=AESModeOfOperation.ModeOfOperation["CBC"]):
    """ Module function to decrypt the given data with the given key.
    
        @param key: key to be used for decryption
        @param data: data to be decrypted with initialization vector prepended
        @param mode: mode of operations (0, 1 or 2)
        @return decrypted data
    """
    keysize = len(key)
    assert keysize in AES.KeySize.values(), 'invalid key size: {}'.format(keysize)
    # iv is first 16 bytes.
    iv = data[:16]
    data = data[16:]
    moo = AESModeOfOperation()
    decr = moo.decrypt(data, None, mode, key, keysize, iv)
    if mode == AESModeOfOperation.ModeOfOperation["CBC"]:
        decr = strip_PKCS7_padding(decr)
    return decr


class Test(object):
    def generateRandomKey(self, keysize):
        """ Generates a key from random data of length `keysize`.    
            The returned key is a string of bytes.    
        """
        if keysize not in (16, 24, 32):
            raise ValueError('Invalid keysize, %s. Should be one of (16, 24, 32).' % keysize)
        return bytearray(os.urandom(keysize))

    def testString(self, cleartext, keysize = 16, modeName = "CBC"):
        """ Test with random key, choice of mode. """
        print('Random key test with Mode:', modeName)
        print('ClearText:', bytes(cleartext))
        key =  self.generateRandomKey(keysize)
        print('Key:', bytes([x for x in key]))
        mode = AESModeOfOperation.ModeOfOperation[modeName]
        cipher = encryptData(key, cleartext, mode)
        print('Cipher:', bytes([x for x in cipher]))
        decr = decryptData(key, cipher, mode)
        print('Decrypted:', bytes(decr))
    
    
if __name__ == "__main__":
    moo = AESModeOfOperation()
    cleartext = "This is a test with several blocks ! Some utf-8 characters åäö and test continues"
    print('ClearText: %s\n' % cleartext)
    cleartext = bytearray(cleartext.encode("utf-8"))
    
    cipherkey = [143, 194, 34, 208, 145, 203, 230, 143, 177, 246, 97, 206, 145, 92, 255, 84]
    iv = [103, 35, 148, 239, 76, 213, 47, 118, 255, 222, 123, 176, 106, 134, 98, 92]
    mode, orig_len, ciph = moo.encrypt(cleartext, moo.ModeOfOperation["CBC"],
                                       cipherkey, moo.aes.KeySize["SIZE_128"], iv)
    
    print('Encrypt result: mode = %s, length = %s (%s), encrypted = %s\n' % (mode, orig_len, len(cleartext), bytes(ciph)))
    
    decr = moo.decrypt(ciph, orig_len, mode, cipherkey, moo.aes.KeySize["SIZE_128"], iv)
    print('Decrypt result: %s\n' % bytes(decr))
    Test().testString(cleartext, 16, "CBC")