title: Why does a Fernet encryption token always start with the same sequence? (Python Cryptography package)
body: <p>I've been playing around with the <a href="https://cryptography.io/" rel="noreferrer">Cryptography package</a>, and the <a href="https://cryptography.io/en/latest/fernet/" rel="noreferrer">Fernet (symmetric encryption) module</a>.</p>
  
  <p>When encrypting some text like:</p>
  
  <pre><code>key = Fernet.generate_key()
  f = Fernet(key)
  token = f.encrypt(b"some random text")
  </code></pre>
  
  <p>The token always starts with the same sequence of bytes like this: <code>"gAAAABU80....."</code>.</p>
  
  <p>Why is this?</p>