C# sample for SRP-6

// SRP-6 sample of client and server
// refer this lib: https://github.com/secure-remote-password/srp.net

static string verifier, salt;
static SrpEphemeral clientEphemeral;
static SrpEphemeral serverEphemeral;

static void DoIt(string[] args)
{
    var user = "vasyan";
    var psw = "123456";
    // register user in a system
    (salt, verifier) = SignUp(user, psw);// (user, salt, verifier) are transferred (open way) to the server and saved in DB
    // log in from client
    clientEphemeral = CLIENT_Login();
    // server receives from user 'user_name' and 'clientEphemeral.Public'
    serverEphemeral = SERVER_AcceptLogin(user, clientEphemeral.Public);
    // client receives from server salt and serverEphemeral.Public
    var clientSession = CLIENT_MakeSession(serverEphemeral.Public);
    // server receives clientSession.Proof and computes session key
    var serverSession = SERVER_AcceptSession(clientSession.Proof);
    if (serverSession == null) return;//! it means client provided wrong user/psw
    // server sends serverSession.Proof to the client to verify, client:
    Log.Warning("CLIENT: verify session...");
    if (CLIENT_VerifySession(clientSession, serverSession.Proof))
        Log.Trace("Session verified!");
    else
        Log.Error("Session FAILED!");
}

static (string, string) SignUp(string user, string psw)
{
    var cliSRP = new SrpClient();
    var salt = cliSRP.GenerateSalt();
    var privateKey = cliSRP.DerivePrivateKey(salt, user, psw);
    var verifier = cliSRP.DeriveVerifier(privateKey);
    return (salt, verifier);
}

static SrpEphemeral CLIENT_Login()
{
    var cliSRP = new SrpClient();
    return cliSRP.GenerateEphemeral();
}

static SrpEphemeral SERVER_AcceptLogin(string user, string cliPubKey)
{
    var srvSRP = new SrpServer();
    return srvSRP.GenerateEphemeral(verifier);// server generates keys using user's verifier, obtained by user_name
}

static SrpSession CLIENT_MakeSession(string srvPubKey)
{
    var cliSRP = new SrpClient();
    var privateKey = cliSRP.DerivePrivateKey(salt, "vasyan", "123456");
    return cliSRP.DeriveSession(clientEphemeral.Secret, srvPubKey, salt, "vasyan", privateKey);
}

static SrpSession SERVER_AcceptSession(string clientSessproof)
{
    var srvSRP = new SrpServer();
    try {
        return srvSRP.DeriveSession(serverEphemeral.Secret, clientEphemeral.Public, salt, "vasyan", verifier, clientSessproof);
    } catch {
        Log.Error("Auth FAILED!");
        return null;
    }
}

static bool CLIENT_VerifySession(SrpSession cliSession, string srvSessProof)
{
    var cliSRP = new SrpClient();
    try {
        cliSRP.VerifySession(clientEphemeral.Public, cliSession, srvSessProof);
    } catch { return false; }
    return true;
}