diff --git a/syllabus/1-Cryptography/4-Encryption-slides.html b/syllabus/1-Cryptography/4-Encryption-slides.html
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 A reader can check the MAC to ensure the message was constructed by someone knowing the secret.
 
+<img style="height: 500px" src="./img/Authenticated_Encryption_EtM.png" />
+
 <aside class="notes"><p>Specifically, this authenticity says that <em>anyone who does not know the sender&#39;s secret</em> could not construct the message.</p>
 <p>Generally, this adds ~16-32 bytes of overhead per encrypted message.</p>
+<p>The image only shows only of of many possible constructions of authenticated encryption.</p>
+<p>Explain that the Key2 in the image, could be derived from Key1.</p>
 </aside></script></section><section  data-markdown><script type="text/template">
 ## AEAD (**A**uthenticated **E**ncryption **A**dditional **D**ata)
 
diff --git a/syllabus/1-Cryptography/img/Authenticated_Encryption_EtM.png b/syllabus/1-Cryptography/img/Authenticated_Encryption_EtM.png
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