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→Example Bootloader
Note details of the AES-CTR nonce, AES-CBC I.V., and key are stored in the firmware itself. In this example they are not downloaded as part of the encrypted firmware file.
== Bootloader Interface Code ==
<syntaxhighlight>
#!/usr/bin/python
# -*- coding: utf-8 -*-
#
# Copyright (c) 2013-2016, NewAE Technology Inc
# All rights reserved.
#
# Authors: Colin O'Flynn, Greg d'Eon
#
# Find this and more at newae.com - this file is part of the chipwhisperer
# project, http://www.assembla.com/spaces/chipwhisperer
#
# This file is part of chipwhisperer.
#
# chipwhisperer is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# chipwhisperer is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with chipwhisperer. If not, see <http://www.gnu.org/licenses/>.
#=================================================
import sys
import time
import chipwhisperer.capture.ui.CWCaptureGUI as cwc
from chipwhisperer.common.api.CWCoreAPI import CWCoreAPI
from chipwhisperer.capture.targets.SimpleSerial import SimpleSerial
from chipwhisperer.common.scripts.base import UserScriptBase
from chipwhisperer.capture.targets._base import TargetTemplate
from chipwhisperer.common.utils import pluginmanager
from chipwhisperer.capture.targets.simpleserial_readers.cwlite import SimpleSerial_ChipWhispererLite
from chipwhisperer.common.utils.parameter import setupSetParam
import logging
# Class Crc
#############################################################
# These CRC routines are copy-pasted from pycrc, which are:
# Copyright (c) 2006-2013 Thomas Pircher <tehpeh@gmx.net>
#
class Crc(object):
"""
A base class for CRC routines.
"""
def __init__(self, width, poly):
"""The Crc constructor.
The parameters are as follows:
width
poly
reflect_in
xor_in
reflect_out
xor_out
"""
self.Width = width
self.Poly = poly
self.MSB_Mask = 0x1 << (self.Width - 1)
self.Mask = ((self.MSB_Mask - 1) << 1) | 1
self.XorIn = 0x0000
self.XorOut = 0x0000
self.DirectInit = self.XorIn
self.NonDirectInit = self.__get_nondirect_init(self.XorIn)
if self.Width < 8:
self.CrcShift = 8 - self.Width
else:
self.CrcShift = 0
def __get_nondirect_init(self, init):
"""
return the non-direct init if the direct algorithm has been selected.
"""
crc = init
for i in range(self.Width):
bit = crc & 0x01
if bit:
crc ^= self.Poly
crc >>= 1
if bit:
crc |= self.MSB_Mask
return crc & self.Mask
def bit_by_bit(self, in_data):
"""
Classic simple and slow CRC implementation. This function iterates bit
by bit over the augmented input message and returns the calculated CRC
value at the end.
"""
# If the input data is a string, convert to bytes.
if isinstance(in_data, str):
in_data = [ord(c) for c in in_data]
register = self.NonDirectInit
for octet in in_data:
for i in range(8):
topbit = register & self.MSB_Mask
register = ((register << 1) & self.Mask) | ((octet >> (7 - i)) & 0x01)
if topbit:
register ^= self.Poly
for i in range(self.Width):
topbit = register & self.MSB_Mask
register = ((register << 1) & self.Mask)
if topbit:
register ^= self.Poly
return register ^ self.XorOut
class BootloaderTarget(TargetTemplate):
_name = 'AES-CCM Bootloader'
def __init__(self):
TargetTemplate.__init__(self)
ser_cons = pluginmanager.getPluginsInDictFromPackage("chipwhisperer.capture.targets.simpleserial_readers", True, False)
self.ser = ser_cons[SimpleSerial_ChipWhispererLite._name]
self.keylength = 16
self.input = ""
self.crc = Crc(width=16, poly=0x1021)
self.setConnection(self.ser)
def setKeyLen(self, klen):
""" Set key length in BITS """
self.keylength = klen / 8
def keyLen(self):
""" Return key length in BYTES """
return self.keylength
def getConnection(self):
return self.ser
def setConnection(self, con):
self.ser = con
self.params.append(self.ser.getParams())
self.ser.connectStatus.connect(self.connectStatus.emit)
self.ser.selectionChanged()
def con(self, scope=None):
if not scope or not hasattr(scope, "qtadc"): Warning(
"You need a scope with OpenADC connected to use this Target")
self.ser.con(scope)
# 'x' flushes everything & sets system back to idle
self.ser.write("xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx")
self.ser.flush()
self.connectStatus.setValue(True)
def close(self):
if self.ser != None:
self.ser.close()
return
def init(self):
pass
def setModeEncrypt(self):
return
def setModeDecrypt(self):
return
def convertVarToString(self, var):
if isinstance(var, str):
return var
sep = ""
s = sep.join(["%c" % b for b in var])
return s
def loadEncryptionKey(self, key):
pass
def loadInput(self, inputtext):
self.input = inputtext
framemsg = [0] * 16
framemsg[15] = 1
logging.debug("Sending header")
self.sendBootloaderMessage(1, framemsg)
logging.debug("Sending auth tag")
self.sendBootloaderMessage(2, [0]*16)
def readOutput(self):
# No actual output
return [0] * 16
def isDone(self):
return True
def checkEncryptionKey(self, kin):
return kin
def go(self):
logging.debug("Sending input data")
self.sendBootloaderMessage(3, self.input)
def sendBootloaderMessage(self, ftype, data):
# Starting byte is 0x01, 0x02, or 0x03
message = [ftype]
# Append 16 bytes of data
message.extend(data)
# Append 2 bytes of CRC for input only (not including type)
crcdata = self.crc.bit_by_bit(data)
message.append(crcdata >> 8)
message.append(crcdata & 0xff)
# Write message
message = self.convertVarToString(message)
self.ser.flush()
self.ser.write(message)
time.sleep(0.05)
data = self.ser.read(1)
if len(data) > 0:
resp = ord(data[0])
if resp != 0xA4:
raise IOError("Failed to communicate, last response: %x" % resp)
else:
raise IOError("Failed to communicate, no response")
</syntaxhighlight>
