/**
* Computes the final session key as a result of the SRP successful mutual authentication
* To be called after verifying the server evidence message M2.
* @return Key: the mutually authenticated symmetric session key
* @throws CryptoException
*/
public virtual BigInteger CalculateSessionKey()
{
// Verify pre-requirements (here we enforce a previous calculation of M1 and M2)
if (this.S == null || this.M1 == null || this.M2 == null)
{
throw new CryptoException("Impossible to compute Key: " +
"some data are missing from the previous operations (S,M1,M2)");
}
this.Key = Srp6Utilities.CalculateKey(digest, N, S);
return(Key);
}