def verify(data, digest)
      if valid_digest?(data, digest)
        true
      else
        raise DynamicImage::Errors::InvalidSignature
      end
    end
def verify(data, digest)
      if valid_digest?(data, digest)
        true
      else
        raise DynamicImage::Errors::InvalidSignature
      end
    end
Verifies that <tt>digest</tt> is valid for <tt>data</tt>.
 Raises a +DynamicImage::Errors::InvalidSignature+ error if not.