def METHOD_NAME(self):
    """
    Return SBox object for self.
    EXAMPLES::
        sage: from sage.crypto.mq.mpolynomialsystemgenerator import MPolynomialSystemGenerator
        sage: msg = MPolynomialSystemGenerator()
        sage: msg.sbox()
        Traceback (most recent call last):
        ...
        AttributeError: '<class 'sage.crypto.mq.mpolynomialsystemgenerator.MPolynomialSystemGenerator'>' object has no attribute '_sbox'
    """
    return self._sbox