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Diffstat (limited to 'plugins/ao/eng_qsf/kabuki.c')
| -rw-r--r-- | plugins/ao/eng_qsf/kabuki.c | 156 |
1 files changed, 156 insertions, 0 deletions
diff --git a/plugins/ao/eng_qsf/kabuki.c b/plugins/ao/eng_qsf/kabuki.c new file mode 100644 index 00000000..61100304 --- /dev/null +++ b/plugins/ao/eng_qsf/kabuki.c @@ -0,0 +1,156 @@ +/*************************************************************************** + +"Kabuki" Z80 encryption + + +The "Kabuki" is a custom Z80 module which runs encrypted code. The encryption +key is stored in some battery-backed RAM, therefore the chip has the annoying +habit of stopping working every few years, when the battery dies. +Check at the bottom of this text to see a list of all the known games which +use this chip. + + +How it works: +The base operation is a bit swap which affects couples of adjacent bits. +Each of the 4 couples may or may not be swapped, depending on the address of +the byte and on whether it is an opcode or data. +The decryption consists of these steps: +- bitswap +- ROL +- bitswap +- XOR with a key +- ROL +- bitswap +- ROL +- bitswap + +To know how to apply the bit swap, take the address of the byte to decode and: +- if the byte is an opcode, add addr_key to the address +- if the byte is data, XOR the address with 1FC0, add 1, and then add addr_key +You'll get a 16-bit word. The first two bitswaps depend on bits 0-7 of that +word, while the second two on bits 8-15. When a bit in the word is 1, swap the +two bits, oherwise don't. The exact couple of bits affected depends on the +game and is identified in this file with two keys: swap_key1 and swap_key2 +(which are just permutations of the numbers 0-7, not full 32-bit integers). + + +Key space size: +- swap_key1 8! = 40320 +- swap_key2 8! = 40320 +- addr_key 2^16 = 65536 +- xor_key 2^8 = 256 +- total 2.7274 * 10^16 + + +Weaknesses: +- 0x00 and 0xff, having all the bits set to the same value, are not affected + by bit permutations after the XOR. Therefore, their encryption is the same + regardless of the high 8 bits of the address, and of the value of + swap_key2. If there is a long stream of 0x00 or 0xff in the original data, + this can be used to find by brute force all the candidates for swap_key1, + xor_key, and for the low 8 bits of addr_key. This is a serious weakness + which dramatically reduces the security of the encryption. +- A 0x00 is always encrypted as a byte with as many 1s as xor_key; a 0xff is + always encrypted as a byte with as many 0s as xor_key has 1s. So you just + need to know one 0x00 or 0xff in the unencrypted data to know how many 1s + there are in xor_key. +- Once you have restricted the range for swap_key1 and you know the number of + 1s in the xor_key, you can easily use known plaintext attacks and brute + force to find the remaining keys. Long strings like THIS GAME IS FOR USE IN + and ABCDEFGHIJKLMNOPQRSTUVWXYZ can be found by comparing the number of 1s + in the clear and encrypted data, taking xor_key into account. When you have + found where the string is, use brute force to reduce the key space. + + +Known games: + swap_key1 swap_key2 addr_key xor_key +Mahjong Gakuen 2 Gakuen-chou no Fukushuu 76543210 01234567 aa55 a5 +Poker Ladies " " " " "" "" +Dokaben " " " " "" "" +Dokaben 2 unknown +Pang / Buster Bros / Pomping World 01234567 76543210 6548 24 +Capcom Baseball " " " " "" "" +Capcom World 04152637 40516273 5751 43 +Adventure Quiz 2 Hatena ? no Dai-Bouken 45670123 45670123 5751 43 +Super Pang 45670123 45670123 5852 43 +Super Buster Bros 45670123 45670123 2130 12 +Super Marukin-Ban 54321076 54321076 4854 4f +Quiz Tonosama no Yabou 12345670 12345670 1111 11 +Ashita Tenki ni Naare unknown +Quiz Sangokushi 23456701 23456701 1828 18 +Block Block 02461357 64207531 0002 01 + +Warriors of Fate 01234567 54163072 5151 51 +Cadillacs and Dinosaurs 76543210 24601357 4343 43 +Punisher 67452103 75316024 2222 22 +Slam Masters 54321076 65432107 3131 19 + +***************************************************************************/ + +#include "cpuintrf.h" + +static int bitswap1(int src,int key,int sel) +{ + if (sel & (1 << ((key >> 0) & 7))) + src = (src & 0xfc) | ((src & 0x01) << 1) | ((src & 0x02) >> 1); + if (sel & (1 << ((key >> 4) & 7))) + src = (src & 0xf3) | ((src & 0x04) << 1) | ((src & 0x08) >> 1); + if (sel & (1 << ((key >> 8) & 7))) + src = (src & 0xcf) | ((src & 0x10) << 1) | ((src & 0x20) >> 1); + if (sel & (1 << ((key >>12) & 7))) + src = (src & 0x3f) | ((src & 0x40) << 1) | ((src & 0x80) >> 1); + + return src; +} + +static int bitswap2(int src,int key,int sel) +{ + if (sel & (1 << ((key >>12) & 7))) + src = (src & 0xfc) | ((src & 0x01) << 1) | ((src & 0x02) >> 1); + if (sel & (1 << ((key >> 8) & 7))) + src = (src & 0xf3) | ((src & 0x04) << 1) | ((src & 0x08) >> 1); + if (sel & (1 << ((key >> 4) & 7))) + src = (src & 0xcf) | ((src & 0x10) << 1) | ((src & 0x20) >> 1); + if (sel & (1 << ((key >> 0) & 7))) + src = (src & 0x3f) | ((src & 0x40) << 1) | ((src & 0x80) >> 1); + + return src; +} + +static int bytedecode(int src,int swap_key1,int swap_key2,int xor_key,int sel) +{ + src = bitswap1(src,swap_key1 & 0xffff,sel & 0xff); + src = ((src & 0x7f) << 1) | ((src & 0x80) >> 7); + src = bitswap2(src,swap_key1 >> 16,sel & 0xff); + src ^= xor_key; + src = ((src & 0x7f) << 1) | ((src & 0x80) >> 7); + src = bitswap2(src,swap_key2 & 0xffff,sel >> 8); + src = ((src & 0x7f) << 1) | ((src & 0x80) >> 7); + src = bitswap1(src,swap_key2 >> 16,sel >> 8); + return src; +} + +static void kabuki_decode(unsigned char *src,unsigned char *dest_op,unsigned char *dest_data, + int base_addr,int length,int swap_key1,int swap_key2,int addr_key,int xor_key) +{ + int A; + int sel; + + for (A = 0; A < length; A++) + { + /* decode opcodes */ + sel = (A + base_addr) + addr_key; + dest_op[A] = bytedecode(src[A],swap_key1,swap_key2,xor_key,sel); + + /* decode data */ + sel = ((A + base_addr) ^ 0x1fc0) + addr_key + 1; + dest_data[A] = bytedecode(src[A],swap_key1,swap_key2,xor_key,sel); + } +} + +void cps1_decode(unsigned char *rom, int swap_key1,int swap_key2,int addr_key,int xor_key) +{ + int diff = (512*1024)/2; + + kabuki_decode(rom, rom+diff, rom, 0x0000, 0x8000, swap_key1, swap_key2, addr_key, xor_key); +} |