Both the request and reply are undocumented.

Client -> Server:
[code](BYTE[20])  Client Password Proof (for old password)
(BYTE[32])  Salt (for new password)
(BYTE[32])  Verifier (for new password)[/code]

Server -> Client:
[code](DWORD)     Result
(BYTE[32])  Server Password Proof ("M[2]") (for old password)

Possible result codes:
    0x00:   Password changed.
    0x02:   Incorrect old password.[/code]

Does the client echo that data back in the response or is that a mistake? The draft format that's present already does not contain M1, s, or v for the server->client message.

It's a mistake.  The information currently available is correct.

Thanks. This has been published now.