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<div class="slides">
<section id="title-slide">
<h1 class="title">CPA Angriff auf Speck</h1>
<p class="author">Robin Dietrich & Marius Schwarz</p>
</section>
<section id="agenda" class="slide level1">
<h1>Agenda</h1>
<ul>
<li>Speck Chiffre</li>
<li>CPA Angriffe</li>
<li>CPA auf Speck</li>
<li>Gegenmaßnahmen</li>
<li>Hiding</li>
</ul>
</section>
<section id="speck" class="slide level1">
<h1>Speck</h1>
<ul>
<li>Symmentrische ARX Chiffre
<ul>
<li>Add/Rotate/XOR</li>
<li>Effizient und einfach umzusetzen</li>
</ul></li>
<li>Entworfen von der NSA (Zusammen mit der Chiffre Simon)</li>
<li>Performant in Hard-/Software</li>
<li>Speck bietet mehrere mögliche Modis
<ul>
<li>Anzahl Runden, Schlüssellänge, Blocklänge</li>
</ul></li>
<li>Paper: <a href="https://csrc.nist.gov/csrc/media/events/lightweight-cryptography-workshop-2015/documents/papers/session1-shors-paper.pdf">Simon and Speck: Block Ciphers for the Internet of Things</a></li>
</ul>
</section>
<section id="speck---setups" class="slide level1">
<h1>Speck - Setups</h1>
<table>
<thead>
<tr class="header">
<th>Speck</th>
<th>Blocklänge</th>
<th>Schlüssellänge</th>
<th>Runden</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td><span style="color:#d08a1d"><strong>Speck3264</strong></span></td>
<td><span style="color:#d08a1d"><strong>32 Bit</strong></span></td>
<td><span style="color:#d08a1d"><strong>64 Bit</strong></span></td>
<td><span style="color:#d08a1d"><strong>22</strong></span></td>
</tr>
<tr class="even">
<td>Speck4872</td>
<td>48 Bit</td>
<td>72 Bit</td>
<td>22</td>
</tr>
<tr class="odd">
<td>Speck4896</td>
<td>48 Bit</td>
<td>96 Bit</td>
<td>23</td>
</tr>
<tr class="even">
<td>Speck6496</td>
<td>64 Bit</td>
<td>96 Bit</td>
<td>26</td>
</tr>
<tr class="odd">
<td>Speck64128</td>
<td>64 Bit</td>
<td>128 Bit</td>
<td>27</td>
</tr>
<tr class="even">
<td>Speck9696</td>
<td>96 Bit</td>
<td>96 Bit</td>
<td>28</td>
</tr>
<tr class="odd">
<td>Speck96144</td>
<td>96 Bit</td>
<td>144 Bit</td>
<td>29</td>
</tr>
<tr class="even">
<td>Speck128128</td>
<td>128 Bit</td>
<td>128 Bit</td>
<td>32</td>
</tr>
<tr class="odd">
<td>Speck128192</td>
<td>128 Bit</td>
<td>192 Bit</td>
<td>33</td>
</tr>
<tr class="even">
<td>Speck1281256</td>
<td>128 Bit</td>
<td>256 Bit</td>
<td>34</td>
</tr>
</tbody>
</table>
</section>
<section id="speck---rundenfunktion" class="slide level1">
<h1>Speck - Rundenfunktion</h1>
<p><img data-src="img/rundenfunktion.png" width="400" /></p>
<ul>
<li>Wird für die Generierung des Rundenschlüssels aufgerufen</li>
<li>Wird bei der Verschlüsselung des Klartextes aufgerufen</li>
<li>Arbeitet auf zwei geteiltem Input</li>
</ul>
</section>
<section id="speck---pseudocode" class="slide level1">
<h1>Speck - Pseudocode</h1>
<div class="sourceCode" id="cb1"><pre class="sourceCode c"><code class="sourceCode c"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a>pt <span class="op">=</span> Plaintext Bytes Pt <span class="op">=</span> Plaintext as <span class="dv">16</span> Bit Words</span>
<span id="cb1-2"><a href="#cb1-2" aria-hidden="true" tabindex="-1"></a>ct <span class="op">=</span> Ciphertext Bytes Ct <span class="op">=</span> Ciphertext as <span class="dv">16</span> Bit Words</span>
<span id="cb1-3"><a href="#cb1-3" aria-hidden="true" tabindex="-1"></a>k <span class="op">=</span> Key as Bytes K <span class="op">=</span> Key as <span class="dv">16</span> Bit Words</span>
<span id="cb1-4"><a href="#cb1-4" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-5"><a href="#cb1-5" aria-hidden="true" tabindex="-1"></a><span class="co">// Key Schedule</span></span>
<span id="cb1-6"><a href="#cb1-6" aria-hidden="true" tabindex="-1"></a>D<span class="op">=</span>K<span class="op">[</span><span class="dv">3</span><span class="op">],</span> C<span class="op">=</span>K<span class="op">[</span><span class="dv">2</span><span class="op">],</span> B<span class="op">=</span>K<span class="op">[</span><span class="dv">1</span><span class="op">],</span> A<span class="op">=</span>K<span class="op">[</span><span class="dv">0</span><span class="op">]</span></span>
<span id="cb1-7"><a href="#cb1-7" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-8"><a href="#cb1-8" aria-hidden="true" tabindex="-1"></a><span class="cf">for</span> i in <span class="fl">0.</span><span class="er">.</span><span class="op"><</span><span class="dv">22</span></span>
<span id="cb1-9"><a href="#cb1-9" aria-hidden="true" tabindex="-1"></a> rk<span class="op">[</span>i<span class="op">]=</span>A</span>
<span id="cb1-10"><a href="#cb1-10" aria-hidden="true" tabindex="-1"></a> ER16<span class="op">(</span>B<span class="op">,</span> A<span class="op">,</span> i<span class="op">++)</span></span>
<span id="cb1-11"><a href="#cb1-11" aria-hidden="true" tabindex="-1"></a> rk<span class="op">[</span>i<span class="op">]=</span>A</span>
<span id="cb1-12"><a href="#cb1-12" aria-hidden="true" tabindex="-1"></a> ER16<span class="op">(</span>C<span class="op">,</span> A<span class="op">,</span> i<span class="op">++)</span></span>
<span id="cb1-13"><a href="#cb1-13" aria-hidden="true" tabindex="-1"></a> rk<span class="op">[</span>i<span class="op">]=</span>A</span>
<span id="cb1-14"><a href="#cb1-14" aria-hidden="true" tabindex="-1"></a> ER16<span class="op">(</span>D<span class="op">,</span> A<span class="op">,</span> i<span class="op">++)</span></span>
<span id="cb1-15"><a href="#cb1-15" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-16"><a href="#cb1-16" aria-hidden="true" tabindex="-1"></a><span class="co">// Encryption</span></span>
<span id="cb1-17"><a href="#cb1-17" aria-hidden="true" tabindex="-1"></a>Ct<span class="op">[</span><span class="dv">0</span><span class="op">]=</span>Pt<span class="op">[</span><span class="dv">0</span><span class="op">];</span> Ct<span class="op">[</span><span class="dv">1</span><span class="op">]=</span>Pt<span class="op">[</span><span class="dv">1</span><span class="op">];</span></span>
<span id="cb1-18"><a href="#cb1-18" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-19"><a href="#cb1-19" aria-hidden="true" tabindex="-1"></a><span class="cf">for</span> i in <span class="fl">0.</span><span class="er">.</span><span class="op"><</span><span class="dv">22</span></span>
<span id="cb1-20"><a href="#cb1-20" aria-hidden="true" tabindex="-1"></a> ER16<span class="op">(</span>Ct<span class="op">[</span><span class="dv">1</span><span class="op">],</span> Ct<span class="op">[</span><span class="dv">0</span><span class="op">],</span> rk<span class="op">[</span>i<span class="op">++])</span></span></code></pre></div>
</section>
<section id="speck---möglicher-angriff" class="slide level1">
<h1>Speck - Möglicher Angriff</h1>
<ul>
<li>Angriff der Rundenfunktion</li>
<li>ADD/XOR/ROT Operationen</li>
</ul>
<div class="sourceCode" id="cb2"><pre class="sourceCode c"><code class="sourceCode c"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="dt">void</span> FuncER16<span class="op">(</span>u16 <span class="op">*</span>x<span class="op">,</span> u16 <span class="op">*</span>y<span class="op">,</span> u16 k<span class="op">)</span></span>
<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a><span class="op">{</span></span>
<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a> u16 tmp_x <span class="op">=</span> <span class="op">*</span>x<span class="op">;</span></span>
<span id="cb2-4"><a href="#cb2-4" aria-hidden="true" tabindex="-1"></a> u16 tmp_y <span class="op">=</span> <span class="op">*</span>y<span class="op">;</span></span>
<span id="cb2-5"><a href="#cb2-5" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-6"><a href="#cb2-6" aria-hidden="true" tabindex="-1"></a> <span class="op">*</span>x <span class="op">=</span> <span class="op">(((</span>tmp_x<span class="op">)>>(</span><span class="dv">7</span><span class="op">))</span> <span class="op">|</span> <span class="op">((</span>tmp_x<span class="op">)<<(</span><span class="dv">16</span><span class="op">-(</span><span class="dv">7</span><span class="op">))));</span> <span class="co">// ROR(7)</span></span>
<span id="cb2-7"><a href="#cb2-7" aria-hidden="true" tabindex="-1"></a> <span class="op">*</span>x <span class="op">+=</span> <span class="op">*</span>y<span class="op">;</span></span>
<span id="cb2-8"><a href="#cb2-8" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-9"><a href="#cb2-9" aria-hidden="true" tabindex="-1"></a> <span class="op">*</span>x <span class="op">=</span> <span class="op">*</span>x <span class="op">^</span> k<span class="op">;</span></span>
<span id="cb2-10"><a href="#cb2-10" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-11"><a href="#cb2-11" aria-hidden="true" tabindex="-1"></a> <span class="op">*</span>y <span class="op">=</span> <span class="op">(((</span>tmp_y<span class="op">)<<(</span><span class="dv">2</span><span class="op">))</span> <span class="op">|</span> <span class="op">(</span>tmp_y<span class="op">>>(</span><span class="dv">16</span><span class="op">-(</span><span class="dv">2</span><span class="op">))));</span> <span class="co">// ROL(2)</span></span>
<span id="cb2-12"><a href="#cb2-12" aria-hidden="true" tabindex="-1"></a> <span class="op">*</span>y <span class="op">=</span> <span class="op">*</span>y <span class="op">^</span> <span class="op">*</span>x<span class="op">;</span></span>
<span id="cb2-13"><a href="#cb2-13" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div>
</section>
<section id="speck---möglicher-angriff-1" class="slide level1">
<h1>Speck - Möglicher Angriff</h1>
<ul>
<li>Der Rundenschlüssel steckt in der XOR Operation:</li>
</ul>
<p><img data-src="img/er16_enc_rk.png" /> <img data-src="img/er16_annot.png" /></p>
</section>
<section id="correlation-power-analysis" class="slide level1">
<h1>Correlation Power Analysis</h1>
<ul>
<li>Variante von Differential Power Analysis (DPA)</li>
<li>Nutzt Pearson Correlation Coefficient (PCC)</li>
<li><strong>Bei Speck:</strong> Korrelation zwischen Power-Trace und Rundenschlüssel</li>
<li>Vorgehen:
<ul>
<li>Modell erstellen</li>
<li>Finden der Korrelationen im Modell</li>
<li>Anwenden auf Hardware Implementierung</li>
</ul></li>
</ul>
</section>
<section id="hamming-weight" class="slide level1">
<h1>Hamming Weight</h1>
<ul>
<li>Passendes Modell zum ‘bewerten’ des Stromverbrauchs</li>
<li>Chip hat ein gewissen Basisverbrauch (IDLE)</li>
<li>Werden Bytes im Chip verändert (<span class="math inline">0 → 1; 1 → 0</span>), wird Strom benötigt</li>
<li>Verhalten kann durch die Hamming-Distanz simuliert werden</li>
<li><strong>Hamming Distanz:</strong> Anzahl der veränderten Bits:</li>
</ul>
<p><span class="math display"><em>H</em><em>D</em>(0100101,0010101) = 2</span></p>
<p>Der Unterschied zweier per XOR verknüpfter Daten, wird als Hamming-Gewicht bezeichnet:</p>
<p><span class="math display"><em>H</em><em>a</em><em>m</em><em>m</em><em>i</em><em>n</em><em>g</em><em>D</em><em>i</em><em>s</em><em>t</em><em>a</em><em>n</em><em>c</em><em>e</em>(0100101,0010101) = <em>H</em><em>a</em><em>m</em><em>m</em><em>i</em><em>n</em><em>g</em><em>W</em><em>e</em><em>i</em><em>g</em><em>h</em><em>t</em>(0100101⊕0010101)</span></p>
</section>
<section id="speck---modell" class="slide level1">
<h1>Speck - Modell</h1>
<ul>
<li>Einfaches Modell der Speck Verschlüsselung</li>
<li>Kann für die ersten 2 Byte des Rundenschlüssels genutzt werden:</li>
</ul>
<div class="sourceCode" id="cb3"><pre class="sourceCode python"><code class="sourceCode python"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true" tabindex="-1"></a><span class="kw">def</span> simple_speck(plaintext, key):</span>
<span id="cb3-2"><a href="#cb3-2" aria-hidden="true" tabindex="-1"></a> Ct_0 <span class="op">=</span> (<span class="bu">int</span>(plaintext[<span class="dv">1</span>]) <span class="op"><<</span> <span class="dv">8</span>) <span class="op">+</span> <span class="bu">int</span>(plaintext[<span class="dv">0</span>]) <span class="co"># RIGHT Key</span></span>
<span id="cb3-3"><a href="#cb3-3" aria-hidden="true" tabindex="-1"></a> Ct_1 <span class="op">=</span> (<span class="bu">int</span>(plaintext[<span class="dv">3</span>]) <span class="op"><<</span> <span class="dv">8</span>) <span class="op">+</span> <span class="bu">int</span>(plaintext[<span class="dv">2</span>]) <span class="co"># LEFT Key</span></span>
<span id="cb3-4"><a href="#cb3-4" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb3-5"><a href="#cb3-5" aria-hidden="true" tabindex="-1"></a> Ct_1, Ct_0 <span class="op">=</span> ER16(Ct_1, Ct_0, key) <span class="co"># Calculate Roundfunction</span></span>
<span id="cb3-6"><a href="#cb3-6" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb3-7"><a href="#cb3-7" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> popcount((Ct_1 <span class="op"><<</span> <span class="dv">8</span>) <span class="op">+</span> Ct_0) <span class="co"># Return Hamming Weight (aka Popcount)</span></span></code></pre></div>
</section>
<section id="speck---simulation" class="slide level1">
<h1>Speck - Simulation</h1>
<ol type="1">
<li>Simulation anhand des Modells mit <span class="math inline"><em>n</em></span> traces</li>
<li>Generieren von <span class="math inline"><em>n</em></span> zufälligen Klartexten mit <strong>fixem</strong> Keybyte (+ noise)</li>
<li>Simulation aller möglichen Keybytes per Hamming Weight</li>
<li>Berechnen des PCC aller Keys über alle traces</li>
</ol>
<p><img data-src="img/simulation_corr.png" /></p>
<p><span class="math inline">→</span> Das korrekte Keybyte ist: 0x68</p>
</section>
<section id="angriff---hardware" class="slide level1">
<h1>Angriff - Hardware</h1>
<ol type="1">
<li>Implementierung von Speck auf CW</li>
<li>Aufzeichnen von <span class="math inline"><em>n</em></span> Power Traces</li>
<li>Leakage Test</li>
<li>Berechnung des Software Modells</li>
<li>Berechnen der Korrelationen zwischen Modell/Powertraces
<ul>
<li>Keybyte für Keybyte</li>
<li>Rückrechnen des Rundenschlüssels</li>
</ul></li>
</ol>
</section>
<section id="t-test" class="slide level1">
<h1>T-Test</h1>
<ul>
<li>Kann verwendet werden, um <em>Leakage</em> zu erkennen
<ul>
<li>Gibt das Berechnen einer Chiffre mehr Information zurück als geplant: Leakage</li>
<li>Ausnutzbar z.B. durch die Power Traces</li>
</ul></li>
<li>Berechnet durch:</li>
</ul>
<p><img data-src="img/ttest_calc.png" /></p>
<ul>
<li>Vergleicht zwei unabhängige Stichproben miteinander</li>
<li>Je unterschiedlicher die Mittelwerte <span class="math inline">→</span> desto mehr Leakage</li>
</ul>
</section>
<section id="t-test-1" class="slide level1">
<h1>T-Test</h1>
<ul>
<li>T-Test der aufgezeichneten Power-Traces:</li>
</ul>
<p><img data-src="img/t_test_original.png" /></p>
<ul>
<li>Erkennbar, dass Leakage vorhanden sein muss</li>
</ul>
</section>
<section id="korrelationen-des-ersten-keybytes" class="slide level1">
<h1>Korrelationen des ersten Keybytes</h1>
<ul>
<li>Korrelationen des ersten Keybytes</li>
<li>Korrelation fällt höher aus als im Modell</li>
<li>Deutliches Maximum der Korrelation bei 0x22 (Korrektes Keybyte)</li>
</ul>
<p><img data-src="img/correlation_first_keybyte.png" width="550" /></p>
</section>
<section id="problem-blocksize" class="slide level1">
<h1>Problem: Blocksize</h1>
<ul>
<li>Bei <strong>Speck3264:</strong> Operationen nicht auf Byte, sondern auf 16-Bit Ebene</li>
<li>Erste Idee: Modell und Korrelation auf <span class="math inline">2<sup>16</sup></span> Keys</li>
<li><span class="math inline">→</span> Keyspace ist abdeckbar (65536 Keys)</li>
<li><span class="math inline">→</span> Zu langsam</li>
<li><span class="math inline">→</span> Nicht möglich für andere Modis von Speck (32 Bit Subkeys)</li>
<li><strong>Lösung:</strong> Modell funktioniert auch auf allen Teilbytes per Shift:</li>
</ul>
<div class="sourceCode" id="cb4"><pre class="sourceCode python"><code class="sourceCode python"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a>rightkey <span class="op">=</span> <span class="bn">0x00</span></span>
<span id="cb4-2"><a href="#cb4-2" aria-hidden="true" tabindex="-1"></a><span class="cf">for</span> guess_key <span class="kw">in</span> <span class="bu">range</span>(<span class="dv">256</span>):</span>
<span id="cb4-3"><a href="#cb4-3" aria-hidden="true" tabindex="-1"></a> leftkey <span class="op">=</span> model( (guess_key <span class="op"><<</span> <span class="dv">8</span>) <span class="op">+</span> righkey )</span>
<span id="cb4-4"><a href="#cb4-4" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb4-5"><a href="#cb4-5" aria-hidden="true" tabindex="-1"></a><span class="cf">for</span> guess_key <span class="kw">in</span> <span class="bu">range</span>(<span class="dv">256</span>):</span>
<span id="cb4-6"><a href="#cb4-6" aria-hidden="true" tabindex="-1"></a> rightkey <span class="op">=</span> model( (leftkey <span class="op"><<</span> <span class="dv">8</span>) <span class="op">+</span> guess_key )</span></code></pre></div>
<ul>
<li>Auch umsetzbar auf Speck mit Blocksize > 16 Bit</li>
</ul>
</section>
<section id="problem-nth-keybytes" class="slide level1">
<h1>Problem: <span class="math inline"><em>n</em><sup><em>t</em><em>h</em></sup></span> Keybytes</h1>
<ul>
<li>Modell kann nur für die ersten zwei Keybytes genutzt werden, da:</li>
</ul>
<div class="sourceCode" id="cb5"><pre class="sourceCode c"><code class="sourceCode c"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a><span class="cf">for</span> i in <span class="fl">0.</span><span class="er">.</span><span class="op"><</span><span class="dv">22</span></span>
<span id="cb5-2"><a href="#cb5-2" aria-hidden="true" tabindex="-1"></a> ER16<span class="op">(</span>Ct<span class="op">[</span><span class="dv">1</span><span class="op">],</span> Ct<span class="op">[</span><span class="dv">0</span><span class="op">],</span> rk<span class="op">[</span>i<span class="op">++])</span></span></code></pre></div>
<ul>
<li>Die bereits bekannten Rundenschlüssel müssen mit eingeschlossen werden</li>
<li>Muss an der richtigen Stelle passieren (<span class="math inline">⊕</span>-Operation)</li>
</ul>
</section>
<section id="problem-nth-keybytes-1" class="slide level1">
<h1>Problem: <span class="math inline"><em>n</em><sup><em>t</em><em>h</em></sup></span> Keybytes</h1>
<ul>
<li>Anpassung des Modells:</li>
</ul>
<div class="sourceCode" id="cb6"><pre class="sourceCode python"><code class="sourceCode python"><span id="cb6-1"><a href="#cb6-1" aria-hidden="true" tabindex="-1"></a> <span class="co"># -------------- for one key -----------------#</span></span>
<span id="cb6-2"><a href="#cb6-2" aria-hidden="true" tabindex="-1"></a> x <span class="op">=</span> ((x <span class="op"><<</span> (<span class="dv">16</span> <span class="op">-</span> ALPHA)) <span class="op">+</span> (x <span class="op">>></span> ALPHA)) <span class="op">&</span> mod_mask <span class="co"># x = ROR(x, 7)</span></span>
<span id="cb6-3"><a href="#cb6-3" aria-hidden="true" tabindex="-1"></a> x <span class="op">=</span> (x <span class="op">+</span> y) <span class="op">&</span> mod_mask <span class="co"># x = ADD(x, y)</span></span>
<span id="cb6-4"><a href="#cb6-4" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb6-5"><a href="#cb6-5" aria-hidden="true" tabindex="-1"></a> x <span class="op">=</span> x <span class="op">^</span> knownkey[<span class="dv">0</span>]</span>
<span id="cb6-6"><a href="#cb6-6" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb6-7"><a href="#cb6-7" aria-hidden="true" tabindex="-1"></a> <span class="co"># -------------- for second key -----------------#</span></span>
<span id="cb6-8"><a href="#cb6-8" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb6-9"><a href="#cb6-9" aria-hidden="true" tabindex="-1"></a> y <span class="op">=</span> ((y <span class="op">>></span> (<span class="dv">16</span> <span class="op">-</span> BETA)) <span class="op">+</span> (y <span class="op"><<</span> BETA)) <span class="op">&</span> mod_mask <span class="co"># y = ROL(y, 2)</span></span>
<span id="cb6-10"><a href="#cb6-10" aria-hidden="true" tabindex="-1"></a> y <span class="op">=</span> y <span class="op">^</span> x <span class="co"># y = XOR(y, x)</span></span>
<span id="cb6-11"><a href="#cb6-11" aria-hidden="true" tabindex="-1"></a> x <span class="op">=</span> ((x <span class="op"><<</span> (<span class="dv">16</span> <span class="op">-</span> ALPHA)) <span class="op">+</span> (x <span class="op">>></span> ALPHA)) <span class="op">&</span> mod_mask <span class="co"># x = ROR(x, 7)</span></span>
<span id="cb6-12"><a href="#cb6-12" aria-hidden="true" tabindex="-1"></a> x <span class="op">=</span> (x <span class="op">+</span> y) <span class="op">&</span> mod_mask <span class="co"># x = ADD(x, y)</span></span>
<span id="cb6-13"><a href="#cb6-13" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb6-14"><a href="#cb6-14" aria-hidden="true" tabindex="-1"></a> x <span class="op">=</span> x <span class="op">^</span> knownkey[<span class="dv">1</span>] <span class="co"># x = XOR(x, k)</span></span>
<span id="cb6-15"><a href="#cb6-15" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb6-16"><a href="#cb6-16" aria-hidden="true" tabindex="-1"></a> <span class="co"># -------------- for third key -----------------#</span></span>
<span id="cb6-17"><a href="#cb6-17" aria-hidden="true" tabindex="-1"></a> <span class="co"># [...]</span></span></code></pre></div>
</section>
<section id="korrelationen-des-ersten-keybytes-1" class="slide level1">
<h1>Korrelationen des ersten Keybytes</h1>
<ul>
<li>Graph zeigt die Korrelationen des ersten Keybytes bis 5000 traces</li>
<li>Ab ~800 Traces hebt sich die Korrelation deutlich hervor</li>
</ul>
<p><img data-src="img/traces.png" width="550" /></p>
</section>
<section id="gegenmaßnahmen" class="slide level1">
<h1>Gegenmaßnahmen</h1>
</section>
<section id="hiding" class="slide level1">
<h1>Hiding</h1>
<ul>
<li>Verstecken des eigentlichen “Leakages” in Rauschen</li>
<li><span class="math inline">→</span> Erhöhung des vorhandenen Rauschens während der Berechnung</li>
<li>Mehrere Möglichkeiten
<ul>
<li>Mischen der Instruction-Order</li>
<li><strong>Hinzufügen von “Dummy Instructionen”</strong></li>
<li>Clock Jitter</li>
</ul></li>
</ul>
</section>
<section id="hiding---code" class="slide level1">
<h1>Hiding - Code</h1>
<ul>
<li><strong>Ansatz:</strong> Korrelation kommt von <code>ER16()</code>
<ul>
<li>Add/XOR/Rotate</li>
</ul></li>
<li>Hinzufügen weitere AXR Operationen um noise zu erhöhen</li>
<li>Ersetzen von jeder XOR Operation mit folgender Implementierung:</li>
</ul>
<div class="sourceCode" id="cb7"><pre class="sourceCode c"><code class="sourceCode c"><span id="cb7-1"><a href="#cb7-1" aria-hidden="true" tabindex="-1"></a><span class="dt">uint16_t</span> XOR<span class="op">(</span><span class="dt">uint16_t</span> a<span class="op">,</span> <span class="dt">uint16_t</span> b<span class="op">,</span> <span class="dt">int</span> random<span class="op">)</span> <span class="op">{</span></span>
<span id="cb7-2"><a href="#cb7-2" aria-hidden="true" tabindex="-1"></a> <span class="dt">uint8_t</span> tmp <span class="op">=</span> random <span class="op">^</span> <span class="bn">0x5F</span><span class="op">;</span></span>
<span id="cb7-3"><a href="#cb7-3" aria-hidden="true" tabindex="-1"></a> tmp <span class="op">^=</span> <span class="op">(</span>random <span class="op">^</span> a<span class="op">);</span></span>
<span id="cb7-4"><a href="#cb7-4" aria-hidden="true" tabindex="-1"></a> tmp <span class="op">^=</span> <span class="op">(</span>tmp <span class="op">^</span> b<span class="op">);</span></span>
<span id="cb7-5"><a href="#cb7-5" aria-hidden="true" tabindex="-1"></a> tmp <span class="op">&=</span> <span class="op">(</span>tmp <span class="op">&</span> a<span class="op">);</span></span>
<span id="cb7-6"><a href="#cb7-6" aria-hidden="true" tabindex="-1"></a> tmp <span class="op">&=</span> <span class="op">(</span>tmp <span class="op">&</span> b<span class="op">);</span></span>
<span id="cb7-7"><a href="#cb7-7" aria-hidden="true" tabindex="-1"></a> <span class="cf">return</span> a <span class="op">^</span> b<span class="op">;</span></span>
<span id="cb7-8"><a href="#cb7-8" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div>
<ul>
<li><code>Random</code> wird bei jeder Verschlüsslung erneut generiert</li>
</ul>
</section>
<section id="hiding---t-test" class="slide level1">
<h1>Hiding - T-Test</h1>
<ul>
<li>Ergebnisse des T-Tests mit implementierter Hiding Maßnahmen:</li>
</ul>
<p><img data-src="img/t_test_hiding_random.png" /></p>
<ul>
<li>Bedarf weiterer Analysen, denn Unterschiede der beiden T-Tests sind nur minimal</li>
<li>Laut T-Test <strong>keine</strong> Indikation dass Hiding funktioniert</li>
</ul>
</section>
<section id="korrelationen-des-ersten-keybytes-2" class="slide level1">
<h1>Korrelationen des ersten Keybytes</h1>
<ul>
<li>Besseres Ergebnis der Korrelationen bis 5000 Traces</li>
<li>Korrelationen flachen ab ~800 drastisch ab</li>
<li>Keine Korrelation sticht heraus</li>
</ul>
<p><img data-src="img/corr_traces_hiding_5k.png" width="550" /></p>
<ul>
<li>Es war nicht möglich den Angriff erneut durchzuführen</li>
<li>Neue Korrelationen nach einigen Test lediglich bei ~0.18 mit falschem Keybyte</li>
<li><span class="math inline">→</span> Maßnahme ist erfolgreich</li>
</ul>
</section>
<section id="hiding-potentieller-bypass" class="slide level1">
<h1>Hiding (potentieller) Bypass</h1>
<ul>
<li>Korrelation sollte weiterhin möglich sein, wenn die Operationen in Betracht gezogen werden</li>
<li>Schwierigkeit hängt am Zufallszahlengenerator</li>
<li><strong>Problem:</strong> Sichere Zufallszahlen auf Embedded Chips sind nicht trivial</li>
</ul>
<p><span class="math inline">→</span> Bypass konnte <strong>nicht</strong> realisiert werden</p>
</section>
<section id="referenzen" class="slide level1">
<h1>Referenzen</h1>
<ul>
<li><a href="Improved%20Differential%20Cryptanalysis%20of%20Round-Reduced%20Speck">Improved Differential Cryptanalysis of Round-Reduced Speck</a></li>
<li><a href="Breaking%20Speck%20cryptosystem%20using%20correlation%20power%20analysis%20attack">Breaking Speck cryptosystem using correlation power analysis attack</a></li>
<li><a href="%7BSpeck-R:%20An%20ultra%20light-weight%20cryptographic%20scheme%20for%20Internet%20of%20Things">Speck-R: An ultra light-weight cryptographic scheme for Internet of Things</a></li>
</ul>
</section>
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