title: Cipher not initialized for encryption/decryption
body: <p>When I run this code:</p>
  
  <pre><code>  public static byte[] unwrap(PrivateKey privateKey, byte[] wrappedKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPWithSHA-256AndMGF1Padding");  
        cipher.init(Cipher.UNWRAP_MODE, privateKey);
  
        return cipher.doFinal(wrappedKey);
    }
  </code></pre>
  
  <p>The return statement line throws this:</p>
  
  <pre><code>Exception in thread "main" java.lang.IllegalStateException: Cipher not initialized for encryption/decryption
      at javax.crypto.Cipher.checkCipherState(Cipher.java:1754)
      at javax.crypto.Cipher.doFinal(Cipher.java:2157)
      at x.y.z.decrypt.Main.unwrap(Main.java:47)
      at x.y.z.decrypt.Main.main(Main.java:33)
  </code></pre>
  
  <p>If I use DECRYPT_MODE it seems to try and decrypt, but I'm after unwrap. Any suggestions?</p>