def HMAC(self, key_bytes, message_bytes):
'''Provides the bytes of the hashed message authentication code. To
convert to hexadecimal, the bytes need to be passed through
MySHA256.hexdigest(result).
Returns the bytes of the hashed message authentication code.'''
# Convert the ipad and the opad to bitarrays
ipadBitArray = self.ipadToBits()
opadBitArray = self.opadToBits()
# Pad the key
paddedKey = self.padKey(key_bytes)
# Fuse the key with the ipad and opad
fusedIpad = self.fusePadWithKey(ipadBitArray, paddedKey)
fusedOpad = self.fusePadWithKey(opadBitArray, paddedKey)
# Prepend the message with the fused ipad
inputMessage = bytearray(fusedIpad.ToBytes())
inputMessage.extend(message_bytes)
# Hash the ipad to begin hashing the message
mySHA = MySHA256()
ipadHashPart = mySHA.hash(BytesToWords(inputMessage))
ipadHashPartBits = MyBitArray()
ipadHashPartBits.FromBytes(ipadHashPart)
# Take the result hash bytes and prepend the fused opad
finalHashInput = MyBitArray()
finalHashInput.FromBytes(fusedOpad.ToBytes())
finalHashInput.extend(ipadHashPartBits)
# Hash the resulting concatenation
result = mySHA.hash(BytesToWords(finalHashInput.ToBytes()))
return result
def padMessage(message_bytes):
''' Pads a given byte array of a message with a 1 followed by 0s and finally the length
of the original message in the last 8 bytes of the last message block.
'''
lastMessageBitIndex = 448
# Guard conditions
if MySHA256.blockLength < 0:
raise ValueError("MySHA256 block length should be set to 512, but is set to a negative number.")
originalMessageLengthBytes = MySHA256.messageLengthToBytes(message_bytes)
if len(originalMessageLengthBytes) > (MySHA256.blockLength - lastMessageBitIndex):
raise ValueError("MySHA256 cannot process a message of this length.")
# Get length of block in bytes
lastBlockLength = (len(message_bytes) % (int(MySHA256.blockLength/8)))
nZeroes = lastMessageBitIndex - 1 - (lastBlockLength * 8)
if nZeroes < 0:
# Add a whole block of padding if necessary, to fit with the padding scheme
nZeroes = MySHA256.blockLength + nZeroes - 1
# Add padding
messageBitArray = MyBitArray()
messageBitArray.FromBytes(message_bytes)
messageBitArray.extend([1])
messageBitArray.extend([0] * nZeroes)
# Append length of the original message
result = bytearray(messageBitArray.ToBytes())
result.extend(originalMessageLengthBytes)
return bytes(result)
def padKey(self, key_bytes):
'''Pads the used key with zeroes on the right until it meets the expected
hash input length. Doesn't return the padded key, just changes it
in-place.'''
paddedKey = MyBitArray()
paddedKey.FromBytes(key_bytes)
if len(paddedKey) < BrownThomasHMAC.expectedBlockLength:
padding = [0] * (len(paddedKey) - BrownThomasHMAC.expectedBlockLength)
padding.extend(paddedKey.bits)
paddedKey.FromBits(padding)
elif len(paddedKey) > BrownThomasHMAC.expectedBlockLength:
paddedKey.bits = paddedKey.bits[:BrownThomasHMAC.expectedBlockLength]
return paddedKey
def fusePadWithKey(self, pad_bit_array, padded_key_bit_array):
'''Fuses a key with the given ipad or opad. XORs the key with the leftmost
bits of the given pad. The pad will not be the same size as the key.
The key will be a smaller size.
Returns the padded key as a bit array.'''
padFirstPart = MyBitArray()
padFirstPart.FromBits(pad_bit_array.bits[:len(padded_key_bit_array)])
resultFirstPart = padFirstPart ^ padded_key_bit_array
result = MyBitArray()
result.FromBits(padFirstPart.bits)
result.extend(pad_bit_array[len(padFirstPart):])
return result
def ProcessPermutation(self, bit_array, permutation_box, is_reversed = False):
# Make resulting bit array
result = MyBitArray()
# Process the permutation
if is_reversed == False:
for x in permutation_box:
result.append(bit_array[x - 1])
else:
# Reverse the permutation
result.bits = [0] * len(bit_array)
for i in range(len(permutation_box)):
result[permutation_box[i] - 1] = bit_array[i]
return result
def RemovePadding(self, padded_block_bit_array):
blockBytes = padded_block_bit_array.ToBytes()
# Search for existence of padding
padByte = self.GetPaddingByte(blockBytes)
if padByte != -1:
endIndex = len(blockBytes) - int(padByte)
unpaddedBytes = bytes(blockBytes[:endIndex])
unpaddedBits = MyBitArray()
unpaddedBits.FromBytes(unpaddedBytes)
return unpaddedBits
else:
originalBitArray = MyBitArray()
originalBitArray.extend(padded_block_bit_array)
return originalBitArray
def ProcessKeySchedule(self, feistel_round_info, is_encryption):
if len(feistel_round_info.KeyLeft) != 28 or len(feistel_round_info.KeyRight) != 28:
raise ValueError("Inappropriate key encountered when processing key schedule.")
if is_encryption == True:
self.RotateKeyHalves(feistel_round_info, is_encryption)
# Get the subkey
preSubkey = MyBitArray()
preSubkey.extend(feistel_round_info.KeyLeft)
preSubkey.extend(feistel_round_info.KeyRight)
subkey = self.ProcessPermutation(preSubkey, self.pc2Box)
if is_encryption == False:
self.RotateKeyHalves(feistel_round_info, is_encryption)
return subkey
def CreateInitializationVector(self):
bitLength = 0
initializationVector = bytearray()
while bitLength < self.expectedBlockLength:
appendage = randint(0, 255)
initializationVector.append(appendage)
bitLength += appendage.bit_length()
if bitLength >= self.expectedBlockLength:
break
resultBitArray = MyBitArray()
resultBitArray.FromBytes(initializationVector)
# Truncate result to expectedBlockLength # of bits
resultBitArray.bits = resultBitArray.bits[:self.expectedBlockLength]
return resultBitArray
def FeistelFunction(self, data_input_right_half, subkey):
# E box (Expansion)
expandedData = self.ProcessPermutation(data_input_right_half, self.expansionBox)
# XOR Mr with round's subkey
sBoxInput = expandedData ^ subkey
# Process through S-boxes
joinedSBoxOutput = MyBitArray()
sBoxes = [self.sBox1, self.sBox2, self.sBox3, self.sBox4, self.sBox5, self.sBox6, self.sBox7, self.sBox8]
for i in range(len(sBoxes)):
index = i * self.sBoxInputLength
sBoxOutput = self.ProcessSBox(sBoxInput[index : index + self.sBoxInputLength], sBoxes[i])
joinedSBoxOutput.extend(sBoxOutput)
# Permute result
result = self.ProcessPermutation(joinedSBoxOutput, self.permutationBox)
return result
