GBA Cheats: Support for encrypted CodeBreaker cheats

CHANGES

@@ -1,6 +1,7 @@
 0.5.0: (Future)
 Features:
  - Game Boy support
+ - Support for encrypted CodeBreaker GBA cheats
 Bugfixes:
  - VFS: Fix reading 7z archives without rewinding first
  - Qt: Fix sending gameStopped twice

src/gba/cheats.c

@@ -133,6 +133,8 @@ void GBACheatSetInit(struct GBACheatSet* set, const char* name) {
 	set->incompletePatch = 0;
 	set->currentBlock = 0;
 	set->gsaVersion = 0;
+	set->cbRngState = 0;
+	set->cbMaster = 0;
 	set->remainingAddresses = 0;
 	set->hook = 0;
 	int i;
@@ -548,6 +550,10 @@ void GBACheatRefresh(struct GBACheatDevice* device, struct GBACheatSet* cheats)
 void GBACheatSetCopyProperties(struct GBACheatSet* newSet, struct GBACheatSet* set) {
 	newSet->gsaVersion = set->gsaVersion;
 	memcpy(newSet->gsaSeeds, set->gsaSeeds, sizeof(newSet->gsaSeeds));
+	newSet->cbRngState = set->cbRngState;
+	newSet->cbMaster = set->cbMaster;
+	memcpy(newSet->cbSeeds, set->cbSeeds, sizeof(newSet->cbSeeds));
+	memcpy(newSet->cbTable, set->cbTable, sizeof(newSet->cbTable));
 	if (set->hook) {
 		if (newSet->hook) {
 			--newSet->hook->refs;

src/gba/cheats.h

@@ -175,6 +175,10 @@ struct GBACheatSet {
 
 	int gsaVersion;
 	uint32_t gsaSeeds[4];
+	uint32_t cbRngState;
+	uint32_t cbMaster;
+	uint8_t cbTable[0x30];
+	uint32_t cbSeeds[4];
 	int remainingAddresses;
 
 	char* name;

src/gba/cheats/codebreaker.c

@@ -1,4 +1,4 @@
-/* Copyright (c) 2013-2015 Jeffrey Pfau
+/* Copyright (c) 2013-2016 Jeffrey Pfau
  *
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
@@ -10,11 +10,192 @@
 #include "gba/io.h"
 #include "util/string.h"
 
+static void _cbLoadByteswap(uint8_t* buffer, uint32_t op1, uint16_t op2) {
+	buffer[0] = op1 >> 24;
+	buffer[1] = op1 >> 16;
+	buffer[2] = op1 >> 8;
+	buffer[3] = op1;
+	buffer[4] = op2 >> 8;
+	buffer[5] = op2;
+}
+
+static void _cbStoreByteswap(uint8_t* buffer, uint32_t* op1, uint16_t* op2) {
+	*op1 = (buffer[0] << 24) | (buffer[1] << 16) | (buffer[2] << 8) | buffer[3];
+	*op2 = (buffer[4] << 8) | buffer[5];
+}
+
+static void _cbDecrypt(struct GBACheatSet* cheats, uint32_t* op1, uint16_t* op2) {
+	uint8_t buffer[6];
+	int i;
+
+	_cbLoadByteswap(buffer, *op1, *op2);
+	for (i = sizeof(cheats->cbTable) - 1; i >= 0; --i) {
+		size_t offsetX = i >> 3;
+		size_t offsetY = cheats->cbTable[i] >> 3;
+		int bitX = i & 7;
+		int bitY = cheats->cbTable[i] & 7;
+
+		uint8_t x = (buffer[offsetX] >> bitX) & 1;
+		uint8_t y = (buffer[offsetY] >> bitY) & 1;
+		uint8_t x2 = buffer[offsetX] & ~(1 << bitX);
+		if (y) {
+			x2 |= 1 << bitX;
+		}
+		buffer[offsetX] = x2;
+
+		// This can't be moved earlier due to pointer aliasing
+		uint8_t y2 = buffer[offsetY] & ~(1 << bitY);
+		if (x) {
+			y2 |= 1 << bitY;
+		}
+		buffer[offsetY] = y2;
+	}
+	_cbStoreByteswap(buffer, op1, op2);
+
+	*op1 ^= cheats->cbSeeds[0];
+	*op2 ^= cheats->cbSeeds[1];
+
+	_cbLoadByteswap(buffer, *op1, *op2);
+	uint32_t master = cheats->cbMaster;
+	for (i = 0; i < 5; ++i) {
+		buffer[i] ^= (master >> 8) ^ buffer[i + 1];
+	}
+	buffer[5] ^= master >> 8;
+
+	for (i = 5; i > 0; --i) {
+		buffer[i] ^= master ^ buffer[i - 1];
+	}
+	buffer[0] ^= master;
+	_cbStoreByteswap(buffer, op1, op2);
+
+	*op1 ^= cheats->cbSeeds[2];
+	*op2 ^= cheats->cbSeeds[3];
+}
+
+static uint32_t _cbRand(struct GBACheatSet* cheats) {
+	// Roll LCG three times to get enough bits of entropy
+	uint32_t roll = cheats->cbRngState * 0x41C64E6D + 0x3039;
+	uint32_t roll2 = roll * 0x41C64E6D + 0x3039;
+	uint32_t roll3 = roll2 * 0x41C64E6D + 0x3039;
+	uint32_t mix = (roll << 14) & 0xC0000000;
+	mix |= (roll2 >> 1) & 0x3FFF8000;
+	mix |= (roll3 >> 16) & 0x7FFF;
+	cheats->cbRngState = roll3;
+	return mix;
+}
+
+static size_t _cbSwapIndex(struct GBACheatSet* cheats) {
+	uint32_t roll = _cbRand(cheats);
+	uint32_t count = sizeof(cheats->cbTable);
+
+	if (roll == count) {
+		roll = 0;
+	}
+
+	if (roll < count) {
+		return roll;
+	}
+
+	uint32_t bit = 1;
+
+	while (count < 0x10000000 && count < roll) {
+		count <<= 4;
+		bit <<= 4;
+	}
+
+	while (count < 0x80000000 && count < roll) {
+		count <<= 1;
+		bit <<= 1;
+	}
+
+	uint32_t mask;
+	while (true) {
+		mask = 0;
+		if (roll >= count) {
+			roll -= count;
+		}
+		if (roll >= count >> 1) {
+			roll -= count >> 1;
+			mask |= ROR(bit, 1);
+		}
+		if (roll >= count >> 2) {
+			roll -= count >> 2;
+			mask |= ROR(bit, 2);
+		}
+		if (roll >= count >> 3) {
+			roll -= count >> 3;
+			mask |= ROR(bit, 3);
+		}
+		if (!roll || !(bit >> 4)) {
+			break;
+		}
+		bit >>= 4;
+		count >>= 4;
+	}
+
+	mask &= 0xE0000000;
+	if (!mask || !(bit & 7)) {
+		return roll;
+	}
+
+	if (mask & ROR(bit, 3)) {
+		roll += count >> 3;
+	}
+	if (mask & ROR(bit, 2)) {
+		roll += count >> 2;
+	}
+	if (mask & ROR(bit, 1)) {
+		roll += count >> 1;
+	}
+
+	return roll;
+}
+
+static void _cbReseed(struct GBACheatSet* cheats, uint32_t op1, uint16_t op2) {
+	cheats->cbRngState = (op2 & 0xFF) ^ 0x1111;
+	size_t i;
+	// Populate the initial seed table
+	for (i = 0; i < sizeof(cheats->cbTable); ++i) {
+		cheats->cbTable[i] = i;
+	}
+	// Swap pseudo-random table entries based on the input code
+	for (i = 0; i < 0x50; ++i) {
+		size_t x = _cbSwapIndex(cheats);
+		size_t y = _cbSwapIndex(cheats);
+		uint8_t swap = cheats->cbTable[x];
+		cheats->cbTable[x] = cheats->cbTable[y];
+		cheats->cbTable[y] = swap;
+	}
+
+	// Spin the RNG some to make the initial seed
+	cheats->cbRngState = 0x4EFAD1C3;
+	for (i = 0; i < ((op1 >> 24) & 0xF); ++i) {
+		cheats->cbRngState = _cbRand(cheats);
+	}
+
+	cheats->cbSeeds[2] = _cbRand(cheats);
+	cheats->cbSeeds[3] = _cbRand(cheats);
+
+	cheats->cbRngState = (op2 >> 8) ^ 0xF254;
+	for (i = 0; i < (op2 >> 8); ++i) {
+		cheats->cbRngState = _cbRand(cheats);
+	}
+
+	cheats->cbSeeds[0] = _cbRand(cheats);
+	cheats->cbSeeds[1] = _cbRand(cheats);
+
+	cheats->cbMaster = op1;
+}
+
 bool GBACheatAddCodeBreaker(struct GBACheatSet* cheats, uint32_t op1, uint16_t op2) {
 	char line[14] = "XXXXXXXX XXXX";
 	snprintf(line, sizeof(line), "%08X %04X", op1, op2);
 	GBACheatRegisterLine(cheats, line);
 
+	if (cheats->cbMaster) {
+		_cbDecrypt(cheats, &op1, &op2);
+	}
+
 	enum GBACodeBreakerType type = op1 >> 28;
 	struct GBACheat* cheat = 0;
 
@@ -75,8 +256,8 @@ bool GBACheatAddCodeBreaker(struct GBACheatSet* cheats, uint32_t op1, uint16_t o
 		cheat->width = 2;
 		break;
 	case CB_ENCRYPT:
-		mLOG(CHEATS, STUB, "CodeBreaker encryption not supported");
-		return false;
+		_cbReseed(cheats, op1, op2);
+		return true;
 	case CB_IF_NE:
 		cheat = GBACheatListAppend(&cheats->list);
 		cheat->type = CHEAT_IF_NE;