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/*==LICENSE==*
CyanWorlds.com Engine - MMOG client, server and tools
Copyright (C) 2011 Cyan Worlds, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
You can contact Cyan Worlds, Inc. by email legal@cyan.com
or by snail mail at:
Cyan Worlds, Inc.
14617 N Newport Hwy
Mead, WA 99021
*==LICENSE==*/
/*****************************************************************************
*
* $/Plasma20/Sources/Plasma/NucleusLib/pnNetCli/pnNcEncrypt.cpp
*
***/
#include "Pch.h"
#pragma hdrstop
namespace pnNetCli {
/****************************************************************************
*
* Diffie-Hellman constants
*
// g and n are pregenerated and published
// (built into both client and server software)
BigNum g(4);
BigNum n; n.RandPrime(kKeyBits, &seed);
// a and x are pregenerated; a is built into server software, and x is
// built into client software
BigNum a; a.Rand(kKeyBits, &seed);
BigNum x; x.PowMod(g, a, n);
// client chooses b and y on connect, and sends y to the server
BigNum b; b.Rand(kKeyBits, &seed);
BigNum y; y.PowMod(g, b, n);
// server computes key: k = y^a mod n
BigNum ka; ka.PowMod(y, a, n);
// client computes key: k = x^b mod n
BigNum kb; kb.PowMod(x, b, n);
***/
COMPILER_ASSERT(IS_POW2(kNetDiffieHellmanKeyBits));
/*****************************************************************************
*
* Private
*
***/
//============================================================================
// TODO: Cache computed keys
static void GetCachedServerKey (
NetMsgChannel * channel,
BigNum * ka,
const BigNum & dh_y
) {
// Get diffie-hellman constants
unsigned DH_G;
const BigNum * DH_A;
const BigNum * DH_N;
NetMsgChannelGetDhConstants(channel, &DH_G, &DH_A, &DH_N);
hsAssert(!DH_N->isZero(), "DH_N must not be zero in encrypted mode");
// Compute the result
ka->PowMod(dh_y, *DH_A, *DH_N);
}
/*****************************************************************************
*
* Module functions
*
***/
//============================================================================
void NetMsgCryptClientStart (
NetMsgChannel * channel,
unsigned seedBytes,
const byte seedData[],
BigNum * clientSeed,
BigNum * serverSeed
) {
unsigned DH_G;
const BigNum * DH_X;
const BigNum * DH_N;
NetMsgChannelGetDhConstants(channel, &DH_G, &DH_X, &DH_N);
if (DH_N->isZero()) { // no actual encryption, but the caller expects a seed
clientSeed->SetZero();
serverSeed->SetZero();
}
else {
// Client chooses b and y on connect
BigNum g(DH_G);
BigNum seed(seedBytes, seedData);
BigNum b; b.Rand(kNetDiffieHellmanKeyBits, &seed);
// Client computes key: kb = x^b mod n
clientSeed->PowMod(*DH_X, b, *DH_N);
// Client sends y to server
serverSeed->PowMod(g, b, *DH_N);
}
}
//============================================================================
void NetMsgCryptServerConnect (
NetMsgChannel * channel,
unsigned seedBytes,
const byte seedData[],
BigNum * clientSeed
) {
// Server computes client key: ka = y^a mod n
const BigNum dh_y(seedBytes, seedData);
GetCachedServerKey(channel, clientSeed, dh_y);
}
} // namespace pnNetCli