'Construct a DSA key from a tuple of valid DSA components.
The modulus *p* must be a prime.
The following equations must apply:
- p-1 = 0 mod q
- g^x = y mod p
- 0 < x < q
- 1 < g < p
:Parameters:
tup : tuple
A tuple of long integers, with 4 or 5 items
in the following order:
1. Public key (*y*).
2. Sub-group generator (*g*).
3. Modulus, finite field order (*p*).
4. Sub-group order (*q*).
5. Private key (*x*). Optional.
:Return: A DSA key object (`_DSAobj`).'

def construct(self, tup):

    key = self._math.dsa_construct(*tup)
    return _DSAobj(self, key)
