// license:BSD-3-Clause // copyright-holders:Nicola Salmoria, David Widel /*************************************************************************** NEC MC-8123 encryption emulation Decryption tables provided by David Widel Decryption algorithm by Nicola Salmoria The NEC MC-8123 is a Z80 with built-in encryption. It contains 0x2000 bytes of battery-backed RAM, when the battery dies the game stops working. It's possible that the CPU would work as a normal Z80 in that case, this hasn't been verified. When the CPU reads a byte from memory, it uses 12 bits of the address and the information of whether the byte is an opcode or not to select a byte in the internal RAM. The byte controls how the decryption works. A special value in the internal RAM instructs the CPU to not apply the decryption algorithm at all. This is necessary for the CPU to be able to use RAM areas normally. In theory, the size of the key would make the encryption quite secure. In practice, the contents of the internal RAM were generated using a linear congruential generator, so the whole key can be generated starting from a single 24-bit seed. The LCG is the same that was used to generate the FD1094 keys. Note that the algorithm skips the special value that would instruct the CPU to not decrypt at that address. void generate_key(uint8_t (&key)[0x2000], uint32_t seed, unsigned upper_bound) { unsigned i; for (i = 0; i < upper_bound; ++i) { uint8_t byteval; do { seed *= 0x29; seed += seed << 16; byteval = (~seed >> 16) & 0xff; } while (byteval == 0xff); key[i] = byteval; } for ( ; i < 0x2000; ++i) key[i] = 0xff; } The known games that use this CPU are: CPU # Game Notes Seed Upper Limit -------- ------------------------- ------------------ ------ ----- 317-0029 Block Gal NEC MC-8123B 651 091755 1800? 317-0030 Perfect Billiard 9451EC 1C00 317-0040 Toki no Senshi - Chrono Soldier 068713 1c00 317-0042 Opa Opa B31FD0 1C00 317-0043 Wonder Boy Monster Land 640708 1C00 317-0054 Shinobi (sound CPU) NEC MC-8123B 652 088992 1800 317-0057 Fantasy Zone 2 ADFACE 1800 317-0064 Ufo Senshi Yohko Chan 880603 1C00 317-0066 Altered Beast (sound CPU) NEC MC-8123B 704 ED8600 1800 317-5002 Gigas 1 & 2 NEC MC-8123 638 234567 1C00 317-5004 Eagle Writer Not Dumped 317-5005 Astro Flash Not Dumped 317-5008 Perfect Billiard 9451EC 1C00 317-5012 Ganbare Chinsan Ooshoubu NEC MC-8123A 804B54 1C00 317-5014 DakkoChan Jansoh NEC MC-8123B 206850 1C00 317-5??? Ninja Kid II (sound CPU) NEC MC-8123A 646 27998D 1800 317-???? Center Court (sound CPU) NEC MC-8123B 703 640506 1800 317-???? Omega 861226 1C00? ***************************************************************************/ #include "emu.h" #include "mc8123.h" DEFINE_DEVICE_TYPE(MC8123, mc8123_device, "mc8123", "MC-8123") //------------------------------------------------- // mc8123_device - constructor //------------------------------------------------- mc8123_device::mc8123_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock) : z80_device(mconfig, MC8123, tag, owner, clock) , m_key(*this, "key") { } namespace { template constexpr u8 BITS(T b) { return u8(1) << b; } template constexpr u8 BITS(T b, U... c) { return (u8(1) << b) | BITS(c...); } } // anonymous namespace u8 mc8123_device::decrypt_type0(u8 val, u8 param, unsigned swap) { if (swap == 0) val = bitswap<8>(val,7,5,3,1,2,0,6,4); if (swap == 1) val = bitswap<8>(val,5,3,7,2,1,0,4,6); if (swap == 2) val = bitswap<8>(val,0,3,4,6,7,1,5,2); if (swap == 3) val = bitswap<8>(val,0,7,3,2,6,4,1,5); if (BIT(param,3) && BIT(val,7)) val ^= BITS(5,3,0); if (BIT(param,2) && BIT(val,6)) val ^= BITS(7,2,1); if (BIT(val,6)) val ^= BITS(7); if (BIT(param,1) && BIT(val,7)) val ^= BITS(6); if (BIT(val,2)) val ^= BITS(5,0); val ^= BITS(4,3,1); if (BIT(param,2)) val ^= BITS(5,2,0); if (BIT(param,1)) val ^= BITS(7,6); if (BIT(param,0)) val ^= BITS(5,0); if (BIT(param,0)) val = bitswap<8>(val,7,6,5,1,4,3,2,0); return val; } u8 mc8123_device::decrypt_type1a(u8 val, u8 param, unsigned swap) { if (swap == 0) val = bitswap<8>(val,4,2,6,5,3,7,1,0); if (swap == 1) val = bitswap<8>(val,6,0,5,4,3,2,1,7); if (swap == 2) val = bitswap<8>(val,2,3,6,1,4,0,7,5); if (swap == 3) val = bitswap<8>(val,6,5,1,3,2,7,0,4); if (BIT(param,2)) val = bitswap<8>(val,7,6,1,5,3,2,4,0); if (BIT(val,1)) val ^= BITS(0); if (BIT(val,6)) val ^= BITS(3); if (BIT(val,7)) val ^= BITS(6,3); if (BIT(val,2)) val ^= BITS(6,3,1); if (BIT(val,4)) val ^= BITS(7,6,2); if (BIT(val,7) ^ BIT(val,2)) val ^= BITS(4); val ^= BITS(6,3,1,0); if (BIT(param,3)) val ^= BITS(7,2); if (BIT(param,1)) val ^= BITS(6,3); if (BIT(param,0)) val = bitswap<8>(val,7,6,1,4,3,2,5,0); return val; } u8 mc8123_device::decrypt_type1b(u8 val, u8 param, unsigned swap) { if (swap == 0) val = bitswap<8>(val,1,0,3,2,5,6,4,7); if (swap == 1) val = bitswap<8>(val,2,0,5,1,7,4,6,3); if (swap == 2) val = bitswap<8>(val,6,4,7,2,0,5,1,3); if (swap == 3) val = bitswap<8>(val,7,1,3,6,0,2,5,4); if (BIT(val,2) && BIT(val,0)) val ^= BITS(7,4); if (BIT(val,7)) val ^= BITS(2); if (BIT(val,5)) val ^= BITS(7,2); if (BIT(val,1)) val ^= BITS(5); if (BIT(val,6)) val ^= BITS(1); if (BIT(val,4)) val ^= BITS(6,5); if (BIT(val,0)) val ^= BITS(6,2,1); if (BIT(val,3)) val ^= BITS(7,6,2,1,0); val ^= BITS(6,4,0); if (BIT(param,3)) val ^= BITS(4,1); if (BIT(param,2)) val ^= BITS(7,6,3,0); if (BIT(param,1)) val ^= BITS(4,3); if (BIT(param,0)) val ^= BITS(6,2,1,0); return val; } u8 mc8123_device::decrypt_type2a(u8 val, u8 param, unsigned swap) { if (swap == 0) val = bitswap<8>(val,0,1,4,3,5,6,2,7); if (swap == 1) val = bitswap<8>(val,6,3,0,5,7,4,1,2); if (swap == 2) val = bitswap<8>(val,1,6,4,5,0,3,7,2); if (swap == 3) val = bitswap<8>(val,4,6,7,5,2,3,1,0); if (BIT(val,3) || (BIT(param,1) && BIT(val,2))) val = bitswap<8>(val,6,0,7,4,3,2,1,5); if (BIT(val,5)) val ^= BITS(7); if (BIT(val,6)) val ^= BITS(5); if (BIT(val,0)) val ^= BITS(6); if (BIT(val,4)) val ^= BITS(3,0); if (BIT(val,1)) val ^= BITS(2); val ^= BITS(7,6,5,4,1); if (BIT(param,2)) val ^= BITS(4,3,2,1,0); if (BIT(param,3)) { if (BIT(param,0)) val = bitswap<8>(val,7,6,5,3,4,1,2,0); else val = bitswap<8>(val,7,6,5,1,2,4,3,0); } else if (BIT(param,0)) { val = bitswap<8>(val,7,6,5,2,1,3,4,0); } return val; } u8 mc8123_device::decrypt_type2b(u8 val, u8 param, unsigned swap) { // only 0x20 possible encryptions for this method - all others have 0x40 // this happens because BIT(param,2) cancels the other three if (swap == 0) val = bitswap<8>(val,1,3,4,6,5,7,0,2); if (swap == 1) val = bitswap<8>(val,0,1,5,4,7,3,2,6); if (swap == 2) val = bitswap<8>(val,3,5,4,1,6,2,0,7); if (swap == 3) val = bitswap<8>(val,5,2,3,0,4,7,6,1); if (BIT(val,7) && BIT(val,3)) val ^= BITS(6,4,0); if (BIT(val,7)) val ^= BITS(2); if (BIT(val,5)) val ^= BITS(7,3); if (BIT(val,1)) val ^= BITS(5); if (BIT(val,4)) val ^= BITS(7,5,3,1); if (BIT(val,7) && BIT(val,5)) val ^= BITS(4,0); if (BIT(val,5) && BIT(val,1)) val ^= BITS(4,0); if (BIT(val,6)) val ^= BITS(7,5); if (BIT(val,3)) val ^= BITS(7,6,5,1); if (BIT(val,2)) val ^= BITS(3,1); val ^= BITS(7,3,2,1); if (BIT(param,3)) val ^= BITS(6,3,1); if (BIT(param,2)) val ^= BITS(7,6,5,3,2,1); // same as the other three combined if (BIT(param,1)) val ^= BITS(7); if (BIT(param,0)) val ^= BITS(5,2); return val; } u8 mc8123_device::decrypt_type3a(u8 val, u8 param, unsigned swap) { if (swap == 0) val = bitswap<8>(val,5,3,1,7,0,2,6,4); if (swap == 1) val = bitswap<8>(val,3,1,2,5,4,7,0,6); if (swap == 2) val = bitswap<8>(val,5,6,1,2,7,0,4,3); if (swap == 3) val = bitswap<8>(val,5,6,7,0,4,2,1,3); if (BIT(val,2)) val ^= BITS(7,5,4); if (BIT(val,3)) val ^= BITS(0); if (BIT(param,0)) val = bitswap<8>(val,7,2,5,4,3,1,0,6); if (BIT(val,1)) val ^= BITS(6,0); if (BIT(val,3)) val ^= BITS(4,2,1); if (BIT(param,3)) val ^= BITS(4,3); if (BIT(val,3)) val = bitswap<8>(val,5,6,7,4,3,2,1,0); if (BIT(val,5)) val ^= BITS(2,1); val ^= BITS(6,5,4,3); if (BIT(param,2)) val ^= BITS(7); if (BIT(param,1)) val ^= BITS(4); if (BIT(param,0)) val ^= BITS(0); return val; } u8 mc8123_device::decrypt_type3b(u8 val, u8 param, unsigned swap) { if (swap == 0) val = bitswap<8>(val,3,7,5,4,0,6,2,1); if (swap == 1) val = bitswap<8>(val,7,5,4,6,1,2,0,3); if (swap == 2) val = bitswap<8>(val,7,4,3,0,5,1,6,2); if (swap == 3) val = bitswap<8>(val,2,6,4,1,3,7,0,5); if (BIT(val,2)) val ^= BITS(7); if (BIT(val,7)) val = bitswap<8>(val,7,6,3,4,5,2,1,0); if (BIT(param,3)) val ^= BITS(7); if (BIT(val,4)) val ^= BITS(6); if (BIT(val,1)) val ^= BITS(6,4,2); if (BIT(val,7) && BIT(val,6)) val ^= BITS(1); if (BIT(val,7)) val ^= BITS(1); if (BIT(param,3)) val ^= BITS(7); if (BIT(param,2)) val ^= BITS(0); if (BIT(param,3)) val = bitswap<8>(val,4,6,3,2,5,0,1,7); if (BIT(val,4)) val ^= BITS(1); if (BIT(val,5)) val ^= BITS(4); if (BIT(val,7)) val ^= BITS(2); val ^= BITS(5,3,2); if (BIT(param,1)) val ^= BITS(7); if (BIT(param,0)) val ^= BITS(3); return val; } u8 mc8123_device::decrypt_internal(u8 val, u8 key, bool opcode) { unsigned type = 0; unsigned swap = 0; u8 param = 0; key ^= 0xff; // no encryption if (key == 0x00) return val; type ^= BIT(key,0) << 0; type ^= BIT(key,2) << 0; type ^= BIT(key,0) << 1; type ^= BIT(key,1) << 1; type ^= BIT(key,2) << 1; type ^= BIT(key,4) << 1; type ^= BIT(key,4) << 2; type ^= BIT(key,5) << 2; swap ^= BIT(key,0) << 0; swap ^= BIT(key,1) << 0; swap ^= BIT(key,2) << 1; swap ^= BIT(key,3) << 1; param ^= BIT(key,0) << 0; param ^= BIT(key,0) << 1; param ^= BIT(key,2) << 1; param ^= BIT(key,3) << 1; param ^= BIT(key,0) << 2; param ^= BIT(key,1) << 2; param ^= BIT(key,6) << 2; param ^= BIT(key,1) << 3; param ^= BIT(key,6) << 3; param ^= BIT(key,7) << 3; if (!opcode) { param ^= BITS(0); type ^= BITS(0); } switch (type) { default: case 0: return decrypt_type0(val, param, swap); case 1: return decrypt_type0(val, param, swap); case 2: return decrypt_type1a(val, param, swap); case 3: return decrypt_type1b(val, param, swap); case 4: return decrypt_type2a(val, param, swap); case 5: return decrypt_type2b(val, param, swap); case 6: return decrypt_type3a(val, param, swap); case 7: return decrypt_type3b(val, param, swap); } } u8 mc8123_device::decrypt(offs_t addr, u8 val, bool opcode) { // pick the translation table from bits fd57 of the address offs_t const tbl_num = bitswap<12>(addr,15,14,13,12,11,10,8,6,4,2,1,0); return decrypt_internal(val, m_key[tbl_num | (opcode ? 0x0000 : 0x1000)], opcode); } void mc8123_device::decode(u8 *rom, u8 *opcodes, unsigned length) { for (unsigned i = 0; i < length; i++) { unsigned const adr = (i >= 0xc000) ? ((i & 0x3fff) | 0x8000) : i; u8 const src = rom[i]; // decode the opcodes opcodes[i] = decrypt(adr, src, true); // decode the data rom[i] = decrypt(adr, src, false); } }