public override void SetKey (AsymmetricAlgorithm key)
{
if (key != null) {
// this will throw a InvalidCastException if this isn't
// a DSA keypair
dsa = (DSA) key;
}
#if NET_2_0
else
throw new ArgumentNullException ("key");
#else
// null is accepted in 1.0/1.1
#endif
}