Changes

To safely tell if the "S" values match, both client and server combine srpA, srpB, and their (independently) generated "S" strings to form a string named "M1". The client sends M1 (along with srpA) in the getToken2() message. The server compares the client's copy of M1 against its own. If they match, the client knew the password and the server can safely respond with the encrypted account data. If they do not match, the client (or a man-in-the-middle attacker) did not know the password, and the client should increment a counter that can trigger defenses against online guessing attacks. The server must then return an error to the client, and '''not''' use or reveal srpK (or the correct M1) in any way.