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Tutorial A5 Breaking AES-256 Bootloader

29 bytes removed, 13:20, 21 June 2016
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# Using the AES-256 key schedule, reverse the 13th and 14th round keys to determine the original AES-256 encryption key.
== Setting up the Hardware ==
This tutorial uses the [[CW1002_ChipWhisperer_Capture_Rev2]] hardware along with the [[CW301_Multi-Target]] board. Note that you '''don't need hardware''' to complete the tutorial. Instead you can download [https://www.assembla.com/spaces/chipwhisperer/wiki/Example_Captures example traces from the ChipWhisperer Site], just look for the traces titled ''AVR: AES256 Bootloader (ChipWhisperer Tutorial #A5)''.
For more information on these jumper settings see [[CW301_Multi-Target]] .
</blockquote>
=== Building/Programming the Bootloader ===
TODO
== Capturing the Traces ==
It is assumed that you've already followed the guide in [[Installing ChipWhisperer]]. Thus it is assumed you are able to communicate with the ChipWhisperer Capture Rev2 hardware (or whatever capture hardware you are using). Note in particular you must have configured the FPGA bitstream in the ChipWhisperer-Capture software, all part of the description in the [[Installing ChipWhisperer]] guide.
=== Communication with the Bootloader ===
=== Running the Capture ===
Capturing the traces will requires a special capture script. This capture script is given in [[#Appendix A Capture Script]]. Running this script will start the ChipWhisperer capture system up with the bootloader communications module inserted. Your attack should look like this:
<li>Finally save this project using the ''File --&gt; Save Project'' option, give it any name you want.</li></ol>
== Analyzing of Power Traces for Key ==
<blockquote><blockquote>'''warning'''
: is present in the 'doc' directory (which will always correspond to your release).
</blockquote></blockquote>
=== 14th Round Key using GUI ===
<ol style="list-style-type: decimal;">
<p>[[File:aes14round_points.png|image]]</p></li></ol>
=== 14th Round Key using Script ===
TODO - see 13th round details.
=== 13th Round Key ===
Attacking the 13th round key requires the use of a script. We cannot configure the system through the GUI, as we have no built-in model for the second part of the AES-256 algorithm. This will demonstrate how we can insert custom models into the system. See [[#Appendix B AES-256 14th Round Key Script]] for complete script used here.
At this point we have the 13th round key: <code>c6 6a a6 12 4a ba 4d 04 4a 22 03 54 5b 28 0e 63</code>
=== 13th and 14th Round Keys to Initial Key ===
If you remember that AES decryption is just AES encryption performed in reverse, this means the two keys we recovered are the 13th and 14th round encryption keys. AES keys are given as an 'initial' key which is expanded to all round keys. In the case of AES-256 this initial key is directly used by the initial setup and 1st round of the algorithm.
<pre>94 28 5d 4d 6d cf ec 08 d8 ac dd f6 be 25 a4 99 c4 d9 d0 1e c3 40 7e d7 d5 28 d4 09 e9 f0 88 a1</pre>
== Analysis of Encrypted Files ==
TODO
== Analysis of Power Traces for IV ==
TODO
pt = aes.decrypt(ct)
return getHW(bytearray(pt)[bnum] ^ guess)</pre>
== Timing Attacks for Signature ==
== Appendix A : Capture Script ==
The following:
sys.exit()</pre>
== Appendix B AES-256 14th Round Key Script ==
'''NB: This script works for 0.10 release or later, see local copy in doc/html directory of chipwhisperer release if you need earlier versions'''
def doAnalysis(self):
self.attack.doAttack()</pre>
== Appendix C AES-256 13th Round Key Script ==
'''NB: This script works for 0.10 release or later, see local copy in doc/html directory of chipwhisperer release if you need earlier versions'''
def doAnalysis(self):
self.attack.doAttack()</pre>
== Appendix D AES-256 IV Attack Script ==
'''NB: This script works for 0.10 release or later, see local copy in doc/html directory of chipwhisperer release if you need earlier versions'''
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