aes.py

#!/usr/bin/python
#
#  AES - Advanced Encryption Standard
# 
# Copyright (c) 2007 	Josh Davis ( http://www.josh-davis.org ),
# 			Laurent Haan ( http://www.progressive-coding.com )
# 
# Licensed under the MIT License ( http://www.opensource.org/licenses/mit-license.php ):
#
import math

class AES:
  #
  #  START AES SECTION
  #

  #structure of 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 ]
  # retrieves a given S-Box Value
  def getSBoxValue(self,num): return self.sbox[num]
  # retrieves a given Inverted S-Box Value
  def getSBoxInvert(self,num): returnself. rsbox[num]
  #
  # Rijndael's key schedule rotate operation
  # rotate the word eight bits to the left
  #
  # rotate(1d2c3a4f) = 2c3a4f1d
  #
  # word is an char array of size 4 (32 bit)
  #
  def rotate(self,word):
    c = word[0]
    for i in range(3): word[i] = word[i+1]
    word[3] = c

    return word
  # 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 ]
  # gets a given Rcon value
  def getRconValue(self,num): return self.Rcon[num]
  # Key Schedule Core
  def core(self,word, iteration):
    # 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
  #
  # Rijndael's key expansion
  # expands an 128,192,256 key into an 176,208,240 bytes key
  # 
  # expandedKey is a pointer to an char array of large enough size
  # key is a pointer to a non-expanded key
  #
  def expandKey(self,key, size, expandedKeySize):
    # current expanded keySize, in bytes
    currentSize = 0
    rconIteration = 1
    # temporary 4-byte variable
    t = [0,0,0,0]

    expandedKey = []
    while len(expandedKey) < expandedKeySize:
      expandedKey.append(0)

    # 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
      for k in range(4): t[k] = expandedKey[(currentSize - 4) + k]
      #
      # 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
  # Adds (XORs) the round key to the state
  def addRoundKey(self,state, roundKey):
    for i in range(16):
      state[i] ^= roundKey[i]
    return state
  # Creates a round key from the given expanded key and the
  # position within the expanded key.
  def createRoundKey(self,expandedKey,roundKeyPointer):
    roundKey = [];
    while len(roundKey) < 16:
      roundKey.append(0)
    for i in range(4):
      for j in range(4):
        roundKey[j*4+i] = expandedKey[roundKeyPointer + i*4 + j]
    return roundKey
  # galois multiplication of 8 bit characters a and b
  def galois_multiplication(self,a, b):
    p = 0
    for counter in range(8):
      if (b & 1) == 1: p ^= a
      if p > 0x100: p ^= 0x100
      # keep p 8 bit
      hi_bit_set = (a & 0x80)
      a <<= 1
      if a > 0x100:
        # keep a 8 bit
        a ^= 0x100
      if hi_bit_set == 0x80:
        a ^= 0x1b
      if a > 0x100:
        # keep a 8 bit
        a ^= 0x100
      b >>= 1
      if b > 0x100:
        # keep b 8 bit
        b ^= 0x100

    return p
  #
  # substitute all the values from the state with the value in the SBox
  # using the state value as index for the SBox
  #
  def subBytes(self,state,isInv):
    for i in range(16):
      if isInv: state[i] = self.getSBoxInvert(state[i])
      else: state[i] = self.getSBoxValue(state[i])
    return state
  # iterate over the 4 rows and call shiftRow() with that row
  def shiftRows(self,state,isInv):
    for i in range(4):
      state = self.shiftRow(state,i*4, i,isInv)
    return state
  # each iteration shifts the row to the left by 1 
  def shiftRow(self,state,statePointer,nbr,isInv):
    for i in range(nbr):
      if isInv:
        tmp = state[statePointer + 3]
        j = 3
        while j > 0:
          state[statePointer + j] = state[statePointer + j-1]
          j -= 1;
        state[statePointer] = tmp
      else:
        tmp = state[statePointer]
        for j in range(3):
          state[statePointer + j] = state[statePointer + j+1]
        state[statePointer + 3] = tmp
    return state
  # galois multipication of the 4x4 matrix
  def mixColumns(self,state,isInv):
    column = [0,0,0,0]
    # iterate over the 4 columns
    for i in range(4):
      # construct one column by iterating over the 4 rows
      for j in range(4): column[j] = state[(j*4)+i]
      # apply the mixColumn on one column
      column = self.mixColumn(column,isInv)
      # put the values back into the state
      for k in range(4): state[(k*4)+i] = column[k]

    return state;
  # galois multipication of 1 column of the 4x4 matrix
  def mixColumn(self,column,isInv):
    mult = []
    if isInv: mult = [14,9,13,11]
    else: mult = [2,1,1,3]
    cpy = [0,0,0,0]
    for i in range(4): cpy[i] = column[i]

    column[0] = self.galois_multiplication(cpy[0],mult[0]) ^ self.galois_multiplication(cpy[3],mult[1]) ^ self.galois_multiplication(cpy[2],mult[2]) ^ self.galois_multiplication(cpy[1],mult[3])
    column[1] = self.galois_multiplication(cpy[1],mult[0]) ^ self.galois_multiplication(cpy[0],mult[1]) ^ self.galois_multiplication(cpy[3],mult[2]) ^ self.galois_multiplication(cpy[2],mult[3])
    column[2] = self.galois_multiplication(cpy[2],mult[0]) ^ self.galois_multiplication(cpy[1],mult[1]) ^ self.galois_multiplication(cpy[0],mult[2]) ^ self.galois_multiplication(cpy[3],mult[3])
    column[3] = self.galois_multiplication(cpy[3],mult[0]) ^ self.galois_multiplication(cpy[2],mult[1]) ^ self.galois_multiplication(cpy[1],mult[2]) ^ self.galois_multiplication(cpy[0],mult[3])
    return column

  # applies the 4 operations of the forward round in sequence
  def aes_round(self,state, roundKey):
    state = self.subBytes(state,False)
    state = self.shiftRows(state,False)
    state = self.mixColumns(state,False)
    state = self.addRoundKey(state, roundKey)
    return state

  # applies the 4 operations of the inverse round in sequence
  def aes_invRound(self,state, roundKey):
    state = self.shiftRows(state,True)
    state = self.subBytes(state,True)
    state = self.addRoundKey(state, roundKey)
    state = self.mixColumns(state,True)
    return state

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

  #
  # Perform the initial operations, the standard round, and the final operations
  # of the inverse aes, creating a round key for each round
  #
  def aes_invMain(self,state, expandedKey, nbrRounds):
    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 -= 0
    state = self.shiftRows(state,True)
    state = self.subBytes(state,True)
    state = self.addRoundKey(state, self.createRoundKey(expandedKey,0))
    return state

  # encrypts a 128 bit input block against the given key of size specified
  def encrypt(self,iput, key, size):
    output = []
    while len(output) < 16:
      output.append(0)
    # the number of rounds
    nbrRounds = 0
    # the 128 bit block to encode
    block = []
    # 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
    else: return None

    # the expanded keySize
    expandedKeySize = (16*(nbrRounds+1))
    #
    # Set the block values, for the block:
    # a0,0 a0,1 a0,2 a0,3
    # a1,0 a1,1 a1,2 a1,3
    # a2,0 a2,1 a2,2 a2,3
    # a3,0 a3,1 a3,2 a3,3
    # the mapping order is a0,0 a1,0 a2,0 a3,0 a0,1 a1,1 ... a2,3 a3,3
    #
    while len(block) < 16:
      block.append(0)
    # iterate over the columns
    for i in range(4):
      # iterate over the rows
      for j in range(4):
        block[(i+(j*4))] = iput[(i*4)+j]

    # expand the key into an 176, 208, 240 bytes key
    # the expanded 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):
      # iterate over the rows
      for l in range(4):
        output[(k*4)+l] = block[(k+(l*4))]
    return output

  # decrypts a 128 bit input block against the given key of size specified
  def decrypt(self,iput, key, size):
    output = []
    while len(output) < 16:
      output.append(0)
    # the number of rounds
    nbrRounds = 0
    # the 128 bit block to decode
    block = []
    # 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
    else: return None

    # the expanded keySize
    expandedKeySize = (16*(nbrRounds+1))
    #
    # Set the block values, for the block:
    # a0,0 a0,1 a0,2 a0,3
    # a1,0 a1,1 a1,2 a1,3
    # a2,0 a2,1 a2,2 a2,3
    # a3,0 a3,1 a3,2 a3,3
    # the mapping order is a0,0 a1,0 a2,0 a3,0 a0,1 a1,1 ... a2,3 a3,3
    #

    # iterate over the columns
    for i in range(4):
      # iterate over the rows
      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):
      # iterate over the rows
      for l in range(4):
        output[(k*4)+l] = block[(k+(l*4))]
    return output

  #
  # END AES SECTION
  #

class AESModeOfOperation:
  #
  # START MODE OF OPERATION SECTION
  #
  aes = AES()

  # structure of supported modes of operation
  modeOfOperation = {
      "OFB":0,
      "CFB":1,
      "CBC":2}
  # converts a 16 character string into a number array
  def convertString(self,string,start,end,mode):
    if end - start > 16: end = start + 16
    if mode == self.modeOfOperation["CBC"]: ar = [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
    else: ar = []

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

  #
  # Mode of Operation Encryption
  # stringIn - Input String
  # mode - mode of type modeOfOperation
  # hexKey - a hex key of the bit length size
  # size - the bit length of the key
  # hexIV - the 128 bit hex Initilization Vector
  #
  def encrypt(self,stringIn,mode,key,size,IV):
    if len(key)%size:
      return None
    if len(IV)%16:
      return None
    # the AES input/output
    plaintext = []
    iput = []
    output = []
    ciphertext = []
    while len(ciphertext) < 16:
      ciphertext.append(0)
    # the output cipher string
    cipherOut = []
    # char firstRound
    firstRound = True
    if stringIn != None:
      for j in range(int(math.ceil(float(len(stringIn))/16))):
        start = j*16
        end = j*16+16
        if j*16+16 > 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] ^ ciphertext[i]
            else:
              iput[i] =  plaintext[i] ^ IV[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

  #
  # Mode of Operation Decryption
  # cipherIn - Encrypted String
  # originalsize - The unencrypted string length - required for CBC
  # mode - mode of type modeOfOperation
  # key - a number array of the bit length size
  # size - the bit length of the key
  # IV - the 128 bit number array Initilization Vector
  #
  def decrypt(self,cipherIn,originalsize,mode,key,size,IV):
    # cipherIn = unescCtrlChars(cipherIn)
    if len(key)%size:
      return None
    if len(IV)%16:
      return None
    # the AES input/output
    ciphertext = []
    iput = []
    output = []
    plaintext = []
    while len(plaintext) < 16:
      plaintext.append(0)
    # the output plain text string
    stringOut = ''
    # char firstRound
    firstRound = True
    if cipherIn != None:
      for j in range(int(math.ceil(float(len(cipherIn))/16))):
        start = j*16
        end = j*16+16
        if j*16+16 > 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):
            stringOut += chr(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):
            stringOut += chr(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 < end:
            for k in range(originalsize-start):
              stringOut += chr(plaintext[k])
          else:
            for k in range(end-start):
              stringOut += chr(plaintext[k])
          iput = ciphertext;
    return stringOut;

  #
  # END MODE OF OPERATION SECTION
  #

if __name__ == "__main__":
  moo = AESModeOfOperation()
  mode,orig_len,ciph = moo.encrypt("This is a test!",moo.modeOfOperation["OFB"],[143,194,34,208,145,203,230,143,177,246,97,206,145,92,255,84],moo.aes.keySize["SIZE_128"],[103,35,148,239,76,213,47,118,255,222,123,176,106,134,98,92])
  print ciph
  decr = moo.decrypt(ciph,orig_len,mode,[143,194,34,208,145,203,230,143,177,246,97,206,145,92,255,84],moo.aes.keySize["SIZE_128"],[103,35,148,239,76,213,47,118,255,222,123,176,106,134,98,92])
  print decr