title: Android - SMS Retriever API - Computing app's hash string problem
body: <p>I am really new in Android and I am trying to implement the SMS Retriever API for using OTP in my app.</p>
  
  <p>I am following this guide:
  <a href="https://developers.google.com/identity/sms-retriever/verify#computing_your_apps_hash_string" rel="noreferrer">https://developers.google.com/identity/sms-retriever/verify#computing_your_apps_hash_string</a></p>
  
  <p>Unfortunately I'm stuck in the part of "<strong>Computing your app's hash string</strong>"</p>
  
  <p>I am quoting here the guide sections, and below each one- my question:</p>
  
  <ol>
  <li><p>Get your app's public key certificate as a lower-case hex string. For example, to get the hex string from your keystore, type the following command</p>
  
  <pre><code>keytool -alias MyAndroidKey -exportcert -keystore MyProduction.keystore | xxd -p | tr -d "[:space:]"
  </code></pre></li>
  </ol>
  
  <p><strong>Where can I find my "public key certificate", and where am I supposed to run this command?</strong></p>
  
  <ol start="2">
  <li>Compute the SHA-256 sum of the combined string.</li>
  </ol>
  
  <p><strong>What is SHA-256 and what does it mean to compute it?</strong></p>
  
  <ol start="3">
  <li>Base64-encode the binary value of the SHA-256 sum. You might need to decode the SHA-256 sum from its output format first.</li>
  </ol>
  
  <p><strong>Can't understand, what am I supposed to do here?</strong></p>