Hash-based Message Authentication Code support.

The update method is used to add data to the message. The digest method is used to extract the message authentication code.

interface HMAC default _HMAC {
  /**
   * Create an [HMAC] object from a [Hash] and a key.
   */
  HMAC(Hash hash, List<int> key);

  /**
   * Add a list of bytes to the message.
   */
  HMAC update(List<int> data);

  /**
   * Perform the actual computation and extract the message digest
   * as a list of bytes.
   */
  List<int> digest();
}