title: attr_encryptor bad decrypt error
body: <p>I used danpal/attr_encryptor gem to encrypt some attribute in my ActiveRecord model.</p>
  
  <pre><code>attr_encrypted :number, :charset =&gt; 'UTF-8', :key =&gt; 'vasya pupkin'
  </code></pre>
  
  <p>and got following error</p>
  
  <pre><code>OpenSSL::Cipher::CipherError: bad decrypt
  </code></pre>
  
  <p>Then I tried to use encrypt_number in rails console and seen different values for the same value of 'number' field when I restarted console. Why?</p>
  
  <pre><code>rails c
  CreditCard.encrypt_number('hello')
  "tRO0BETHrh5J3gXv8WVntw==\n"
  quit
  rails c
  CreditCard.encrypt_number('hello')
  "kJSbe30RQyR+gy3oDXv5ZA==\n"
  </code></pre>