// license:BSD-3-Clause // copyright-holders:Morten Shearman Kirkegaard, Samuel Neves, Peter Wilhelmsen /************************************************************************* atarixga.cpp Atari XGA encryption FPGA ************************************************************************** Part numbers: 136094-0072 Moto Frenzy 136095-0072 Space Lords ? Road Riot's Revenge 136094-0004A Primal Rage ? T-Mek *************************************************************************/ #include "atarixga.h" extern const device_type ATARI_XGA = &device_creator; atari_xga_device::atari_xga_device(const machine_config &mconfig, const char *tag, device_t *owner, UINT32 clock) : device_t(mconfig, ATARI_XGA, "Atari XGA", tag, owner, clock, "xga", __FILE__), m_mode(FPGA_RESET), m_address(0), m_ciphertext(0) { } /************************************* * * Initialization * *************************************/ void atari_xga_device::device_start() { m_ram = std::make_unique(RAM_WORDS); save_pointer(NAME(m_ram.get()), RAM_WORDS * sizeof(UINT16)); save_item(NAME(m_address)); save_item(NAME(m_ciphertext)); } void atari_xga_device::device_reset() { memset(m_ram.get(), 0, RAM_WORDS * sizeof(UINT16)); m_mode = FPGA_RESET; m_address = 0; m_ciphertext = 0; } /************************************* * * Definitions * *************************************/ // TODO: Add definitions for other games // Moto Frenzy /* key 0x10 is special, it has 15 "identical twins". */ static const UINT8 kmap[128] = { 0x6B,0x11,0x1B,0x19,0x4B,0x50,0x17,0x09, 0x5D,0x69,0x43,0x33,0x0F,0x0C,0x28,0x3F, 0x00,0x20,0x15,0x3C,0x57,0x38,0x00,0x07, 0x49,0x25,0x61,0x2F,0x2B,0x4E,0x64,0x00, 0x45,0x41,0x6D,0x52,0x31,0x66,0x22,0x59, 0x00,0x70,0x6F,0x5B,0x46,0x6E,0x67,0x5A, 0x26,0x30,0x2C,0x65,0x21,0x3D,0x58,0x00, 0x5E,0x44,0x0D,0x40,0x6C,0x1C,0x51,0x0A, 0x35,0x2A,0x13,0x4D,0x63,0x00,0x00,0x3A, 0x00,0x48,0x54,0x24,0x60,0x1E,0x2E,0x01, 0x56,0x03,0x37,0x00,0x04,0x00,0x05,0x06, 0x00,0x55,0x1F,0x02,0x36,0x14,0x00,0x3B, 0x5F,0x0E,0x1D,0x0B,0x27,0x2D,0x3E,0x00, 0x00,0x5C,0x47,0x68,0x42,0x53,0x32,0x23, 0x4A,0x62,0x4F,0x00,0x00,0x16,0x39,0x08, 0x6A,0x34,0x10,0x29,0x12,0x1A,0x4C,0x18 }; /************************************* * * Decryption * *************************************/ UINT16 atari_xga_device::ctz(UINT16 x) { UINT16 n = 0; if (x == 0) return 16; if (!(x & 0x00FF)) n += 8, x >>= 8; if (!(x & 0x000F)) n += 4, x >>= 4; if (!(x & 0x0003)) n += 2, x >>= 2; if (!(x & 0x0001)) n += 1, x >>= 1; return n; } size_t atari_xga_device::popcount(UINT16 x) { size_t count = 0; while (x != 0) { count += 1; x &= x - 1; } return count; } UINT16 atari_xga_device::parity(UINT16 x) { return popcount(x) & 1; } UINT16 atari_xga_device::lfsr1(UINT16 x) { UINT16 bit = parity(x & 0x8016); return (x << 1) | bit; } UINT16 atari_xga_device::lfsr2(UINT16 x) { UINT16 bit = parity(x & 0x002D); return (x >> 1) | (bit << 15); } UINT16 atari_xga_device::powers2(UINT8 k, UINT16 x) { static const UINT16 L[16] = { 0x5E85,0xBD0B,0x2493,0x17A3, 0x2F47,0x0005,0x000B,0x0017, 0x002F,0x005E,0x00BD,0x017A, 0x02F4,0x05E8,0x0BD0,0x17A1 }; UINT16 t = (x == 16) ? (L[4] ^ L[5]) : L[x]; for (size_t i = 0; i < k; ++i) { t = lfsr1(t); } return t; } UINT16 atari_xga_device::decipher(UINT8 k, UINT16 c) { UINT16 bit, i, p = 0; /* Only 128 keys internally, if high bit set, then find the 7-bit "twin" by xor 0xA8. */ if (k & 0x80) k ^= 0xA8; k = kmap[k]; if ((c & (c - 1)) == 0) { return powers2(k, ctz(c)); } for (bit = 0; bit < 5; ++bit) { if ((c >> bit) & 1) { p ^= powers2(k, bit); } } for (bit = 5; bit < 16; ++bit) { if ((c >> bit) & 1) { p ^= powers2(k, bit + 1); } } UINT16 x = 0x8010; for (i = 0; i < k + 3; ++i) { if (x == c) { return (p == 1) ? 0 : lfsr2(p); } x = lfsr2(x); } return p; } /************************************* * * Write/Read access * *************************************/ WRITE32_MEMBER(atari_xga_device::write) { switch (m_mode) { case FPGA_RESET: return; case FPGA_SETKEY: /* Write table to FPGA SRAM. */ if (ACCESSING_BITS_16_31) m_ram[offset << 1] = UINT16 (data >> 16); if (ACCESSING_BITS_0_15) m_ram[(offset << 1) + 1] = UINT16(data & 0xFFFF); break; case FPGA_DECIPHER: /* Send Ciphertext to FPGA for decryption. */ if (ACCESSING_BITS_16_31) { m_address = offset << 2; m_ciphertext = UINT16(data >> 16); } if (ACCESSING_BITS_0_15) { m_address = (offset << 2) + 2; m_ciphertext = UINT16(data & 0xFFFF); } break; } } READ32_MEMBER(atari_xga_device::read) { UINT32 plaintext = 0; switch (offset << 2) { case 0x0FC0: m_mode = FPGA_RESET; break; case 0x0010: m_mode = FPGA_SETKEY; break; case 0x0020: m_mode = FPGA_DECIPHER; break; } if (m_mode == FPGA_RESET) { return 0; } if (m_mode == FPGA_DECIPHER) { UINT16 address = (offset << 2) - 0x400; if (ACCESSING_BITS_0_15) address += 2; /* Reply with decrypted plaintext */ if (address == m_address) { UINT16 key_offset, key_byte; /* Algorithm to select key byte based on offset. */ key_offset = ((((address >> 4) & 1) ^ 1) << 0) ^ ((((address >> 2) & 1) ^ 0) << 1) ^ ((((address >> 8) & 1) ^ 0) << 2) ^ ((((address >> 3) & 1) ^ 1) << 3) ^ ((((address >> 1) & 1) ^ 1) << 4) ^ ((((address >> 6) & 1) ^ 0) << 5) ^ ((((address >> 7) & 1) ^ 0) << 6) ^ ((((address >> 5) & 1) ^ 1) << 7) ^ ((((address >> 9) & 1) ^ 0) << 8) ^ ((((address >> 10) & 1) ^ 0) << 9); key_byte = m_ram[key_offset]; /* And now for the full magic. */ plaintext = decipher(key_byte, m_ciphertext); if (ACCESSING_BITS_16_31) plaintext <<= 16; } } return plaintext; }