Changes

{{Warningbox|This tutorial will introduce you to measuring the power consumption of a device under attackhas been updated for ChipWhisperer 4. It will demonstrate how 0.0 release. If you can view are using 3.x.x see the "V3" link in the difference between a 'add' instruction and a 'mul' instructionsidebar.}}

{{Infobox tutorial|name = Prerequisites B2: Viewing Instruction Power Differences|image =|caption = |software versions =|capture hardware = CW-Lite, CW-Lite 2-Part, CW-Pro|Target Device = |Target Architecture = XMEGA/Arm/Other|Hardware Crypto = No|Purchase Hardware = }}

You should have already completed [[Tutorial_B1_Building_a_SimpleSerial_Project]]. This tutorial assumes will introduce you are capable of building a new AVR/XMEGA code, programming the code, and connecting to measuring the ChipWhispererpower consumption of a device under attack.It will demonstrate how you can view the difference between assembly instructions== Prerequisites ==

= Setting Up You should have already completed [[Tutorial_B1_Building_a_SimpleSerial_Project]]. This tutorial assumes you are capable of building firmware for the Example =target, programming the code, and connecting to the ChipWhisperer.

<li><p>Copy the directory <code>simpleserial-base</code> which is found at <code>chipwhisperer\hardware\victims\firmware\</code> of the chipwhisperer release to a new directory called <code>simpleserial-base-lab2</code>. You must keep it in the same directory, as it will reference other files within that directory for the build process.</p><p>If you just completed [[Tutorial_B1_Building_a_SimpleSerial_Project]], you can simply reuse that code (this builds upon it).</p><p>At this point we want to modify the system to perform a number of operations. We won't actually use the input data. To do so, open the file <code>simpleserial-base.c</code> with a text editor such as Programmer's Notepad (which ships with WinAVR).</p></li>

<li><p>Change the terminal to the directory with your source, and run the same <code>make</code> command you did earlier to build the systemfirmware. Remember you can press the up arrow on the keyboard to get recently typed commands in most OSes:</p><pre>make</preol><p>Which should have the following output, you will '''want to check the build platform is what you expect''':</p><pre>...Bunch of lines removed...Creating Extended Listing: simpleserial-base.lssavr-objdump -h -S -z simpleserial-base.elf &gt; simpleserial-base.lss

Creating Symbol Table: simpleserial-base.sym== Hardware Setup ==avr-nm -n simpleserial-baseThe hardware setup is the same as in [[Tutorial B1 Building a SimpleSerial Project|Tutorial B1 Building a SimpleSerial Project.elf &gt; simpleserial-base]] The setup is repeated in the drop down menus below, but if you've already done that, skip to the next section.sym{{CollapsibleSection|intro = === CW1173 (Lite) Hardware Setup ===|content= CWLite HW Setup}}

Program: 1568 bytes {{CollapsibleSection|intro = === CW308 (1.1% FullUFO)Hardware Setup ===(.text + .data + .bootloader)|content= CW308 HW Setup}}

Data: 224 bytes (2.7% Full)== Programming the Target ==(.data + Programming the target is the same as in previous tutorials.bss + The steps are repeated in the drop down menus below.noinit)

 == Capturing Power Traces ==

<li>As Under the ''Scope ModulePython Console''tab, select find the ''ChipWhisperer/OpenADCconnect_cwlite_simpleserial.py'' optionscript and double-click.</li><li>As Check there are no errors on the ''Target Module'', select the ''Simple Serial'' optionconnection.</li><li>Switch to Under the ''Target SettingsPython Console'' tab, and as find the ''connection'', select the ''ChipWhisperer'' (relevant setup script for CW1002) or ''ChipWhisperer-Lite'' your target (for CW1173 or CW1180such as setup_cwlite_xmega.py).</li><li>Switch to the ''Scope Settings'' tab, and ensure the ''connection'' is set to either ''ChipWhisperer'' (for CW1002) or ''ChipWhispererdouble-Lite'' (for CW1173 or CW1180)click.</li><li>Run the master connect (click the button labeled ''Master: DIS''). Both the Target &amp; Scope should switch to ''CON'' and be green circles.</li><li><p>For Open the CW1173/CW1180 status monitor (ChipWhisperer-Lite based systems), perform the following:</pi><blockquoteTools ><ol style="list-style-type: lower-alpha;"><li>Set the ''CLKGEN'' frequency to ''7.37 MHz''Encryption Status Monitor</lii><li>Set the*Target HS-IO Out* as ''CLKGEN''</li></ol></blockquote></li><li>If targetting an XMEGA board (either the ChipWhisperer-Lite XMEGA default target, or the XMEGA on the multi-target board), perform the following:<ol style="list-style-type: lower-alpha;"><li>Set ''Target IO1'' as ''Serial RXD''.</li><li>Set ''Target IO2'' as ''Serial TXD''</li></ol></li><li>Switch to the ''General Settings'' tab, and hit the ''Open Monitor'' button.</li></ol> ; 10. Hit the ''Run 1'' [[File:Capture One Button.PNG|image]] button. You may have to hit it a few times, as the very first serial data is often lost. You should see: data populate in the ''Text Out'' field of the monitor window. The ''Text In'' and ''Text Out'' aren't actually used in this example, so you can close the ''Monitor'' dialog.</li>

[[File:cap104_ADC_Clock_2_1.png|image]] <ol start="11" style="list-style-type: decimal;"><li>Under ''Trigger Setup'' set the ''Mode'' to ''rising edge''. This means the system will trigger on a rising edge logic level:</li></ol> [[File:cap2.png|image]] <ol start="12" style="list-style-type: decimal;"><li>For the CW1002 (ChipWhisperer Capture Rev 2) hardware only, perform the following:</li></ol> <blockquote><ol style="list-style-type: lower-alpha;"><li>Under the ''Trigger Pins'' unselect the ''Front Panel A'' as an option, and select ''Target IO4 (Trigger Line)''. This will mean only the trigger pin coming from the AVR target is used to trigger the capture.</li><li><p>In the same area, select the ''Clock Source'' as being from ''Target IO-IN''</p><p>[[File:cap3.png|image]]</p></li><li>You can monitor the ''Freq Counter'' option, which measures the frequency being used on the ''EXTCLK'' input. This should be 7.37 MHz, which is the oscillator on the multi-target board.</li><li>Change the ''ADC Clock'' ''source'' as being ''EXTCLK x4 via DCM''. This routes the external clock through a 4x multiplier, and routes it to the ADC.</li></ol></blockquote><ol start="13" style="list-style-type: decimal;"><li>For the CW1173/CW1180 (ChipWhisperer-Lite based hardware), perform the following:</li></ol> <blockquote><ol start="4" style="list-style-type: lower-alpha;"><li>Change the ''ADC Clock'' ''source'' as being ''CLKGEN x4 via DCM''. This routes the device clock through a 4x multiplier, and routes it to the ADC.</li></ol></blockquote><ol start="14" style="list-style-type: decimal;"><li>Hit the '''Reset ADC DCM''' button.</li></ol> [[File:cap5.png|image]]

<ol start="158" style="list-style-type: decimal;"><li>The ''ADC Freq'' should show 4x the clock speed of your device (typically 29.5 MHz (which is 4x 7.37 MHz5MHz), and the ''DCM Locked'' checkbox __MUST__ be checked. If the ''DCM Locked'' checkbox is NOT checked, try hitting the ''Reset ADC DCM'' button again.</li>

<p>[[File:cap605_Low_Gain.pngPNG|image|1083x1083px]]</p><p>Whilst there is a waveform, you need to adjust the capture settings. There are two main settings of importance, the analog gain and number of samples to capture.</p></li></ol>

[[File:cap706_high_gain.pngPNG|image|1083x1083px]]</ol>

<ol start="1716" style="list-style-type: decimal;"><li>Under ''Gain Setting'' set the ''Mode'' to ''high''. Increase the ''Gain Setting'' to about 25. You'll be able to adjust this further during experimentations, experimentation; you may need to increase this depending on your hardware and target device. For the multi-target board with the CW1002 you will probably need to set this around 40 for example.</li>

== Modifying the Target ==

=== Background on Setup (XMEGA) ===

This The rest of this tutorial is using either an AtMega328p which is an Atmel AVR devicewill focus on AtXMEGA128D4 (the CW303 XMEGA target), or AtXMEGA128D4 which since correlating instructions to power consumption is an Atmel XMEGA devicetypically simpler on it. We are comparing the power consumption of two different instructions, the <code>MUL</code> (multiply) instruction and the <code>NOP</code> (no operation) instruction. Some information on these two instructions:

: ;* Multiples two 8-bit numbers together.;* Takes 2 clock cycles to complete;* Intuitively expect fairly large power consumption due to complexity of operation required

: ;* Does nothing;* Takes 1 clock cycle to complete;* Intuitively expect low power consumption due to core doing nothing

==== Initial Code ====

==== Increase number of NOPs ====

==== Add NOP loop after MUL ====

 ==== Comparison of All Three ====

 === Background on Setup (Arm) ===For the rest of this tutorial, we'll be focusing on the STM32F3, which is the microcontroller on the CW303 Arm target (though other targets should demonstrate the same principles). Since the STM32F3 is an Arm Cortex M4 device, we'll need to refer to the [http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0553a/CHDJJGFB.html Cortex M4 Instruction Set] and the [http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0439b/CHDDIGAC.html Cortex M4 Instruction Set Summary].  The first thing we'll do is replace the <code>nop</code> instructions, since from it's documentation page we can see the processor may not execute them. Instead, let's add some <code>add.w</code> (which is the 32 bit wide version of the add instruction) instructions. We'll be doing this since the <code>mul</code> instruction is always 32 bits wide and the 16 bit thumb instruction has a different power profile than the 32 bit Arm instruction. From the earlier links, we can see that both add and mul take 1 cycle each to complete.  Now we should have 10 <code>add.w</code> instructions and 10 <code>mul</code> instructions:<syntaxhighlight lang="c">trigger_high();  asm volatile("add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t"::); asm volatile("mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t"::); trigger_low();</syntaxhighlight>Now hit the ''Run 1'' [[File:Capture One Button.PNG|image]] button and capture a single trace. You should now have something that looks like this: [[File:B2 STM Addmul.PNG|frameless|1155x1155px]] We can see the <code>add.w</code> and <code>mul</code> instructions near the beginning, staring about 10 samples in and ending about 90 samples in. There's not really any difference that we can see between the two, but we can see that they take up about 80 samples (20 microcontroller clock cycles) as we expect.  Next, let's insert some <code>udiv</code> instructions. From the Cortex M4 Instruction Set Summary, we can see that <code>udiv</code> (unsigned divide) instructions take between 2 and 12 cycles to complete (effectively depending on how big the numbers we're dividing are). We'll be dividing <code>r0</code> by <code>r0</code>, meaning we expect that every instruction after the first should take 2 cycles. It should have higher power consumption too, since dividing is typically a fairly complex operation:<syntaxhighlight lang="c">trigger_high(); asm volatile("add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t""add.w r0, r0" "\n\t"::);asm volatile("mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t""mul r0, r0" "\n\t"::); asm volatile("udiv r0, r0" "\n\t""udiv r0, r0" "\n\t""udiv r0, r0" "\n\t""udiv r0, r0" "\n\t""udiv r0, r0" "\n\t""udiv r0, r0" "\n\t""udiv r0, r0" "\n\t""udiv r0, r0" "\n\t""udiv r0, r0" "\n\t""udiv r0, r0" "\n\t"::); trigger_low();</syntaxhighlight>Capture another trace and you should get something like: [[File:B2 STM Addmuldiv.PNG|frameless|1155x1155px]] As we expected, we can see periods of high power consumption measuring about 80 samples in total right after the <code>add.w</code> and <code>mul</code> instructions. Interestingly, the <code>udiv</code> instructions seem to be split into 2 sets of operations. As a final check, we can add some more <code>mul</code> instructions and see the <code>udiv</code> instructions move down (and also break into more sections):  [[File:B2 STM Addmulmuldiv.PNG|frameless|1155x1155px]]  == Clock Phase Adjustment ==

== Conclusion == In this tutorial you have learned how power analysis can tell you the operations being performed on a microcontroller. In future work we will move towards using this for breaking various forms of security on devices. In particular, [[Tutorial B3-1 Timing Analysis with Power for Password Bypass]] will examine how we can use this information to exploit a password check. == Links ==